Using a Pololu JrK Card to Fine-tune the Calibration of Thrust Levers

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OEM NG style thrust lever

The throttle quadrant for many enthusiasts is the ‘holy grail’ of the simulator, and many individuals strive to ensure that the throttle operates as close as possible to its real world counterpart. 

The automated systems in the 737 aircraft drive the movement of the thrust levers in a coordinated manner, and it’s the accuracy, speed, and  synchronised movement that enthusiasts try to replicate.

Historical Context

Individuals often use Leo Bodnar Joystick cards, PoKeys, Arduino, and Phidget Advanced Servo cards to interface the throttle quadrant (and other hardware) with some using SIOC (a programming language) to connect propriety throttle quadrants.  Calibration, more often than not, was done via FSUPIC, or in a rudimentary way through ProSim737.

Although the throttle quadrant functioned, the position of the levers didn’t match the correct position for the commanded thrust (%N1), and the thrust levers would often be offset against each other and not move in a synchronised manner.  These shortcomings lead to the throttle being used only in ‘manual mode’, as the feedback from the software to the throttle didn’t generate consistent and reliable results. 

Two innovations have changed this – the introduction of Direct Calibration in ProSim-AR, and the development of the Pololu Jrk Interface Card. 

In this article, I’ll explain how to the calibrate the thrust levers using Direct Calibration in ProSim737.  I’ll also show you how to initially calibrate, and then fine-tune the Pololu Jrk card, to enable seamless integration with ProSim737.  Finally, I’ll discuss some advantages that using a Pololu card brings.

Important Point:

  • The calibration settings displayed in the various figures (Figures 1-5) are specific to one simulator.  The Pololu card settings in your simulator will be similar, however, some settings will be different because of subtle differences in the hardware being used.

ProSim-AR - Direct Calibration

ProSim-AR enables direct calibration of the various flight controls and surfaces directly within ProSim737.  This has been inline with their philosophy of trying to keep everything in-house (homogeneous) within ProSim-AR.  This not only enables ProSim-AR to maintain control of how the calibration process occurs, but it also aids in troubleshooting should a problem occur. 

Direct Calibration is a step forward in keeping ‘everything under one roof’ as opposed to using FSUPIC or another programming language to connect aircraft-related assignments.  It’s possible to use direct calibration for the: throttle levers, flaps lever, tiller, speedbrake, aileron, elevator and rudder.

On a side note, Direct Calibration is one of the strengths of ProSim-AR, in addition to built-in native support (via their SDK and generic driver) for various interface cards (which includes the Pololu card).

Pololu JrK Interface card

Pololu Jrk Interface Card

The Pololu Jrk Interface card is a powerful and highly configurable 12v12 brushed DC motor controller, that provides a stable and robust solution to interface the automated movement of the thrust levers in a simulator environment.  Not only are the cards small, but they have been trialled extensively in robotic assignments; NASA uses an upmarket version of the Pololu JrK card to control aspects of the Mars Lander.

The card comes packed with a number of advanced features that enable you to tweak the interaction of the card with ProSim737 which, when combined with a quality 12 volt DC motor and string potentiometer will guarantee higher accuracy and better performance than when other calibration methods are used. 

Using ProSim737 and a Pololu Jrk Card to Calibrate Thrusts Levers 1 and 2

The engineering required to enable movement of the thrust levers is comparatively simple.

Each thrust lever is connected with a string potentiometer that in turn connects with a Pololu JrK card.  The Pololu card then connects directly to the computer by a USB connection.  This creates a closed loop system in which the Pololu card reads the movement of the potentiometers and sends this information to ProSim737 and then to flight simulator.

Obviously, two Pololu cards and two potentiometers are needed; one for each thrust lever, and the calibration of each thrust lever must be carefully done to enable both levers to move together in unison.  Additionally, two 12 volt DC motors are needed to provide the power to move the thrust levers.

To connect and calibrate a Pololu JrK card requires three steps (in sequential order):

(i)      Download and install the Pololu software;

(ii)     Turn on Pololu support in ProSim737 (Configuration/Drivers);

(iii)    Configure the initial settings in the Pololu Configuration Utility (PCU);

(iv)    Calibrate the thrust levers in ProSim737 (Configuration/Levers); and

(v)     Fine-tune the calibration in the Pololu JrK card using the Pololu Configuration Utility (PCU).

Once Pololu support has been selected in ProSim737, the Pololu card will be read automatically by ProSim-AR, and the calibrated settings sent to flight simulator. 

Important Point:

  • Initial configuration in the Pololu card (iii) must be done prior to calibrating the thrust levers in ProSim737 (iv).

Subtle Differences (Hardware)

Every throttle quadrant is different as we use different hardware, potentiometers, and DC motors.  It’s important to understand that, subtle differences in the hardware used in the throttle quadrant, will affect which settings are used to configure the Pololu card.

The following may have a direct effect on the accuracy, speed, synchronisation, and movement of the thrust levers.

(i)     Type of 12 Volt DC motor used;

(ii)    Variable output between DC motors;

(iii)   Type of potentiometer and the manufacturing variance (+/-) between units;

(iv)   The friction generated by each of the thrust levers; and,

(v)    The manufacturing variance (+/-)between each of the Pololu cards.

The type of potentiometer used will make a difference to how accurately the Pololu card can read the movement of the thrust levers.  If an inexpensive linear potentiometer is used, then the accuracy will continually degrade as the carbon trail on the potentiometer is slowly destroyed.  This will lead to frequent recalibration and fine-tuning of the settings. Using a string potentiometer will resolve this issue as contamination leading to loss in calibration is minimal. Use of a Hall sensor will deliver an even greater degree of accuracy (as these sensors are extremely accurate), although it’s debateable to exactly how much more accuracy will be achieved in the movement of the thrust levers, and whether this will be noticed. 

High-end string potentiometers and Hall sensors are often used in the medical industry where the tiniest input movement needs to be accurately measured.  In comparison, the movement of the thrust levers (input) is quite rough.

Performance can also be affected by the type of 12 volt DC Motor used.  If the motor has an amperage either too high or low, or the incorrect gear ratio, the thrust levers may be over or under powered, and no matter what finesse in calibration, the results will be less than optimal. 

Also, depending on the type of throttle you’re using, the friction caused by the thrust levers moving will also be different; some levers move relatively easily while others require additional torque from the DC motor to move.

Interestingly, if you’re using an OEM throttle, there may also be differences between throttle unit builds, as each throttle quadrant is manufactured to be within a range of specific tolerances (manufacturing variance).  For example, the friction needed to be overcome to move the thrust levers is often different between throttle quadrants, and even respective levers on the same quadrant.

RAW data from thrust lever 1 during automated flight.  The upward and downward spikes signify major departure from acceptable operation.  The red line demonstrates how the spikes can be flattened when a Pololu card is used

Calibration of the thrust levers in ProSim737 without using a Pololu card does a reasonable job, however, the output is often quite rough – think of a graph with lots of upward and downward spikes. 

For consistent smooth operation the spikes shown in Figure 6 must be smoothed down.  A Pololu card enables fine-tuning of this output to achieve a consistent and repeatable output

Installing the Pololu JrK Card Software and Initial Configuration

Although ProSim-AR will automatically read the Pololu card, you’ll still need to install the Pololu software to enable access to the Pololu Configuration Utility (PCU).

Two Pololu JrK cards installed to Throttle Interface Module (TIM).  The compact size of the cards is readily apparent.  These cards deliver a big ‘punch’ for such a small size

After downloading the software from Pololu, open the ZIP archive and run ‘Setup.exe’. If the installer fails, you may have to extract all the files to a temporary directory, right click ‘Setup.exe’, and select ‘Run As Administrator’.

The installer will guide you through the steps required to install the Pololu Jrk Configuration Utility, the JrK Command-line Utility (JrkCmd), and the JrK drivers on your computer.

Once the software has been installed, there should be an entry for the JrK in the ‘Pololu USB Devices’ category of the Device Manager. This represents the card’s native USB interface, and it is used by the configuration software. 

Recommendation:

  • Create a shortcut to the Pololu Configuration Utility (PCU) and save this shortcut to your desktop or menu system.  This will enable quicker and easier access to the utility.

Limitation

For brevity and simplicity, I haven’t discussed every configuration setting in the PCU.  Instead, I’ve included several screen captures (Figures 1-5) that show the various configuration settings for reference.  These settings should provide a benchmark to enable you to configure the card. 

Notwithstanding this, I have enlarged on the two most important settings in the PCU that have a direct influence on the accuracy, and synchronised movement of the thrust levers. 

Confirming the Pololu Card Connection

After the initial configuration settings in the Pololu card have been configured, it’s a good idea to test the card’s functionality to confirm connection with ProSim737.  This is done by opening the Pololu Configuration Utility (PCU) and setting a manual target speed (Figure 1).  To engage the target speed, select ‘Apply’. 

Pressing ‘Apply’ will command the card to determine the position of the thrust lever as indicated by the potentiometer.  If the thrust lever is not at the same position on the throttle arc as indicated by the settings in the PCU (and it probably won’t be), the thrust lever will move to the commanded position.  If this movement occurs, it’s a good sign that everything is functioning correctly.

Calibrating Thrust Levers in ProSim737

Assuming everything is working, the next step is to calibrate the thrust levers in ProSim737.

Calibrating the movement of the thrust levers is comparatively straightforward.  Each thrust lever must be calibrated independently of each other, otherwise both levers will not move in unison when the automation (aircraft autopilot) is selected.

(i)     Enable Pololu support in Configuration/Drivers tab in the ProSim737 User Interface;

(ii)    Open the Configuration/Levers tab and assign for each throttle lever the Pololu input and output;

(iii)   Select the appropriate Pololu card for the analogue input and select ‘Feedback input’(1);

(iv)   Select the appropriate Pololu card for server output and then select ‘Motor output’(1); and,

(v)    Move the virtual sliding tab with the mouse (you should see the respective thrust lever moving).

(1) Located in adjacent drop down box.

To calibrate each thrust lever the virtual sliding bar is moved with the mouse device.  To register the position the ‘Min’ and ‘Max’ is selected. 

Slide the bar until the physical thrust lever rests in the idle position (the physical thrust lever should move as you slide the bar).  When the thrust lever is in the idle position select ‘Set Min’.  Next, move the virtual sliding bar until the position of the physical throttle lever rests in the fully forward position.  When it does select ‘Set Max’. 

For calibration to occur, the minimum and maximum positions must be registered.  This process must be completed for both thrust levers.

Important Points:

  • On some set-ups the ProSim737 software reads the throttle movements backwards.  In other words the position of the thrust lever will move in the wrong direction.  If this occurs, reverse the order - press ‘Set Max’ instead of ‘Set Min’ and ‘Set Min’ instead of ‘Set Max’.

  • Calibration occurs when the virtual sliding bar is moved with the mouse device.  Calibration is NOT done by physically moving the thrust levers.

  • To improve accuracy, select ‘Min’ and ‘Max’ only when the physical thrust lever has reached the end of its movement cycle.  This task may need to be done a few times to ensure the most accurate position is registered by the calibration process.

  • Ensure the option ‘closed loop autothrottle’ is NOT selected within the ProSim737 MCP software (right click the virtual MCP to open the MCP Config menu.

  • It’s recommended to use string potentiometers or Hall sensors to register the incremental movements of the thrust levers.  These will provide a greater degree of accuracy.

  • Always calibrate the thrust levers in ProSim737 prior to fine-tuning the Motor and PID in the PCU Interface.

  • It’s at the discretion of the user to calibrate and fine-tune the Pololu card to a level of accuracy they believe is a reasonable compromise between the position of the thrust levers on the throttle arc, and the speed at which the thrust levers move.

Fine-tuning Using The Pololu Configuration Utility (PCU) Tabs

To fine-tune the outputs from the throttle quadrant, the PCU must be opened.  The two tabs that are used to determine the accuracy, position, speed, and synchronisation of the thrust levers are the Motor and PID tabs.

The Motor Tab in the PCU (Figure 4) can be used to alter the current (amperage) and the duty cycle.  Both settings affect the output of the motor (which in turn alters the speed that the thrust levers move).

If the motor has an amperage either too high or low, then the speed that the thrust levers move at, may either be too slow or too fast.  Furthermore, DC motors often exhibit manufacturing variances (+/-)and it’s common to have 2 identical motors with slightly differing output.

If the output is not equalised between the two motors, the position of the thrust levers will be staggered and synchronisation between each of the levers won’t be possible.  Likewise, a different power output may be required to overcome the internal friction of the thrust lever, to enable movement of the lever to occur, . 

Tweaking the motor duty cycle will help eliminate these differences enabling synchronisation of the thrust levers.

The PID Tab in the PCU (Figure 3), an acronym for proportional coefficient, enables in-depth fine- tuning to be applied to the already completed calibration done in ProSim737.

Depending on the power (torque) of the DC motor and the hardware used in the throttle quadrant, the thrust levers may jitter (backward and forward movement when a constant %N1 is set).  To eliminate jitter, the PID is fine-tuned until a happy medium is discovered.

Consistency and Reliability

For the most part, Pololu Jrk cards are manufactured to a high quality and are very reliable; you shouldn’t experience a problem with a card.  Even so, there may be manufacturing variance (+/-)between respective cards.  However, because of the nature of the card, any subtle differences in output can easily be controlled through fine-tuning. 

The above said, the calibration of the thrust levers includes many variables that are interrelated, and to achieve consistent results, the components that provide information to the card, in particular the potentiometers and DC motors, must be of the highest quality.

Important Point:

  • If something doesn’t work as expected, try again using different variables.

Advantages Using a Pololu JrK Card

The benefits of using Pololu Jrk cards cannot be underestimated. 

(i)    Direct support (reading of card) by ProSim-AR;

(ii)   Small size enabling mounting almost anywhere; and,

(iii)  Fine-tuning and increased accuracy through use of the PSU User Interface.

Will I Notice A Difference Using a Pololu JrK Card

The question frequently asked is: ‘will I see a difference if a Pololu card is used’  The answer is not straightforward, as there are several interrelated variables (already discussed).  If the calibration is done carefully in ProSim737 and the variables tweaked in the Pololu PCU, there is no reason why there shouldn’t be a marked improvement.

Final Call

Evolution is rarely static, with change being positive, negative or neutral. 

Direct calibration has enabled greater accuracy in calibrating the various control surfaces within ProSim737 and, in concert with using an advanced card such as the Pololu JrK card, has been a evolutionary step forward.  This has lead to greater accuracy in the position of the thrust levers on the throttle arc, and almost perfect synchronisation, when automation is selected.

Further Information

This is but a short introduction to calibrating the throttle quadrant (thrust levers) directly within ProSim737 using the Pololu Jrk interface card.  For further information concerning the Polulu Jrk card and it’s use with ProSim-TS navigate to the ProSim737 forum and search Polulu. The Polulu website is also worth reading at Pololu.

Acronyms and Glossary

  • Manufacturing Variance (+/-) – This is where identical items, although appearing exactly the same are very slightly different.  Usually the tolerance is so small that it’s indiscernible.  However, manufacturing variance in electronics often is the reason why some parts function and some fail soon after first use.  An acceptable tolerance will be defined at the point of manufacture.  Usually, if an item requires a higher (tighter) tolerance this leads to a higher manufacturing and purchase price.  Often, but not always, there is a direct relationship between the price paid for an item and the reliability and longevity of that item.

  • MCP – Mode Control Panel

  • PCU – Pololu Configuration Utility

  • Throttle Arc – The curved piece of aluminium that the thrust levers move within.

Figures 1–5 display the settings for each of the tabs in the Pololu Jrk Configuration Utility  (PCU).  Note that these settings are generic to all throttles, however, the variables will differ slightly depending upon hardware used.

Repair Backlighting on Throttle Quadrant

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The rear of the First Officer side trim lightplate showing one of the two terminals that the wiring loom connects to

During a recent flight, I noticed that the bulbs that illuminate the backlighting for the trim and flaps lightplate (First Officer side) had failed, however, the backlighting on the Captain-side trim lightplate was illuminated.  My first thought was that the 5 volt bulbs that are integrated into the lightplate had burned out; after all, everything has an end life.

Backlighting - Wiring Loom

The wiring loom that supplies the power for the backlighting enters the throttle quadrant via the front firewall, and initially connects with the trim lightplate and parking brake release light on the Captain-side.  A Y-junction bifurcates the wire loom from the Captain-side to the First Officer side of the quadrant, before it snakes its way along the inside edge of the quadrant firewall to connect with the First Officer side trim lightplate, and then the flaps lightplate.  The wiring loom is attached securely to the inside edge of the throttle casing by screwed cable clamps.

The backlighting for all lightplates is powered by 5 volts and the backlighting on the throttle quadrant is turned on/off/dimmed by the pedestal lighting dimmer knob located on the center pedestal. 

Finding the Problem

Ascertaining whether the bulbs are burned out is uncomplicated, however, assessing the terminals on the rear of each lightplate, and the wiring loom the connects to the lightplates, does involve dismantling part of the throttle quadrant.

The upper section of the throttle quadrant must be dismantled (trim wheels, upper and side panels, and the saw tooth flaps arc).  This enables the inside of throttle quadrant to be inspected more easily with the aid of a torch (lamp/flashlight).  When removing the trim wheels, be especially vigilant not to accidently pull the spline shaft from its mount, as doing so will cause several cogs to fall out of position causing the trim mechanism to be inoperable.

After the lightplates have been removed, but still connected to the wiring loom, a multimeter is used to read the voltage of each respective terminal on the lightplate. If the mutlimeter indicates there is power to the terminals, then the bulbs should illuminate. 

What surprised me when this was done, was that the bulbs worked perfectly. Therefore, it was clear the problem was not bulb, but wire related.

Process of Elimination

The process of elimination is the easiest method to solve problems that may develop in complicated systems.  By reducing the components to their simplest form, a solution can readily be attained.

Alligator wire connects power from Captain-side lightplate to the First Officer lightplate.  Note the frayed outer layer of the white aircraft wire.  The gold colour is a thin layer of gold that acts as a fire retardant should the wiring overheat

If you suspect that the wiring is the problem, and don't have a multi meter, then a quick and fool safe method is to connect an alligator cable from the positive terminal of the Captain-side lightplate to the respective terminal on the First Officer lightplate.  Doing this removes that portion of the wiring harness from the circuit. 

In this scenario, the  bulbs illuminated on both trim lightplates.  As such, the problem was not bulb related, but was associated with the wiring loom.

It must be remembered that the wire used to connect the backlighting in the throttle quadrant is OEM wire.  As such, the age of the wire is the same age as the throttle quadrant.  

Inspecting the wire loom, I noticed that one of the wires that connected to the terminal of the lightplate was severed (cut in two).   I also noted that the original aircraft wires had begun to shed their protective insulation layer. 

Aircraft Wire and Insulation Layers

The high voltage and amperages that travel through aircraft wire can generate considerable heat.  This is why aircraft wire is made to very exacting standards and incorporates several layers of insulation that surround the stranded stainless steel wire.  The use of high-grade stainless steel also provides good strength and resistance to corrosion and oxidation at elevated temperatures.  

The green wire has been severed.  A possible scenario was that the wiring loom had been pulled slightly loose from the throttle chassis, and had become caught in the flaps mechanism.  When the flaps lever is moved, the mechanism can easily crimp (and eventually sever) any wire in its path.  If you observe the white wire you can see the insulation that is shedding

Interestingly, one of the insulating layers is comprised of gold (Au).  The gold acts as an effective fire retardant should the wires overheat.

The breakdown of the upper insulating layer is not a major cause for concern, as a 'shedding' wire still has enough insulation to not arc or short circuit.  However, the wire should be replaced if more than one layer is compromised, or the stainless threads of the wire are visible.

Possible Scenario

When inspecting the wiring loom, I noted that one of the screws that holds the cable clamp to the inside of the throttle casing was loose.  This resulted in part of the wire loom to 'hang' near the flaps arc mechanism.    It is possible that during the throttle’s operational use, the movement and vibration of the aircraft had caused the screw to become loose resulting in the wires hanging down further than normal.  It appears that the wire had been severed, because it became caught in the mechanism of the flaps lever.  

Unlike reproduction throttles, the parts used in an OEM throttle are heavy duty and very solid; they are designed to withstand considerable abuse.  The speedbrake lever, when activated can easily cut a pencil in two, and the repeated movement of the flaps lever, when moved quickly between the teeth of the flaps arc, can easily crimp or flatten a wire.

Rather than try to solder the wires together (soldering stainless wire is difficult) and possibly have the same issue re-occur, I routed the wires from both lightplates (trim and flaps) directly to the 5 volt bus bar located in the center pedestal. 

I could have removed the wire loom completely and replaced it with another loom, however, this would involve having to disassemble the complete upper structure of the throttle quadrant to access the wire loom attachment points on the inside of the throttle casing; something I was not keen to do.

Final Call

OEM parts, although used in a static and simulated environment can have drawbacks.  Apart from age, the repeated movement of mechanical parts and the vibration of the spinning trim wheels, can loosen screws and nuts that otherwise should be securely tightened. 

Acronyms

  • OEM – Original Equipment Manufacturer

  • Wire Loom – Several wires bundled together and attached to a fixed point by some type of clamp

Replacement Curtains - B737 OEM Throttle Dust Curtains

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OEM dust covers for the Boeing throttle. there are slight colour variation depending upon manufactuer

Interesting items can arrive in the post.  Earlier today I opened a small parcel to find a collection of grey coloured pieces of material.  To anyone else they would appear exactly as they do – pieces of material stamped with numbers.

The throttle quadrant I use is original equipment manufacture (OEM) and once plied the skies above Europe.  As such it is a used item with the usual wear and tear you expect from a well-used aircraft part. 

One item that continually caught my attention was the dust curtains or skirts that sit behind the two thrust levers.  In my throttle, the curtains had been abused at some point and were torn and the edges looked rather ragged in appearance.  Although a replacement curtain could have been made by using vinyl or another similar material it would not be the same. 

The numbered pieces of material now have a home – they are OEM dust curtains that will replace the damaged curtains on the throttle.

Installing the Dust Curtains

The B737 throttle quadrant has three dust curtains.  Two on the outer side of the thrust levers and one double-sided curtain that resides between the thrust levers.  Each curtain comprises three parts sandwiched together and held by three screws. 

The parts are:

(i)     The thin aluminium arc which is the outer face plate;

(ii)    The actual curtain; and,

(iii)   The plastic arc retainer. 

Dust curtains have been removed and the plastic retainer and aluminium arc can be seen along with one of the three attachment screws

The plastic arc retainer is curve-shaped and sits flush against the bare metal of the quadrant.  The dust curtain then lies above the retainer and beneath the outer face plate.

Replacing the curtains is straightforward. Remove the three screws that hold the metal arc in place to the throttle, then gentle pry loose the aluminium strip beneath which are the dust curtain and plastic arc retainer.  It’s wise to ensure that you place the parts anatomically on the workbench as each of the items must be reassembled the same way it was removed.

One aspect of Boeing philosophy which makes building a flight simulator much easier is their reuse of parts from earlier airframes.  Boeing do not always redesign a part from scratch, but add to or change existing parts.  This philosophy can save the company millions of dollars.

For those who study this type of thing, you will know that dust curtains can come in differing colour shades.  In general, the older classic style throttle used a paler grey/cream coloured skirt whilst the Next Generation airframes use a standard light grey colour.  But, I would not get too concerned if the colour does not exactly match.

Why are the Dust Curtains Important

The main purpose of the dust curtains is to minimise the chance of foreign bodies falling into the throttle mechanism.  Think pens, rubbers, straws, paper clips and coke can pull tabs (or anything else pilots play with in the flight deck).  The dust curtains are made from a fire retardant material (not asbestos) which minimises the chance of any fire/sparks from licking up the sides of the thrust levers in the unlikely event that a fire devlops inside the throttle quadrant.

For those keen to find replacement OEM dust curtains the stock numbers are: 69-33918-8 REF, 69-33918-9 REF-F and 69-33918-10 REF-F.

Glossary

  • Anatomically – Meaning items removed are placed on a table in the same position as they were when they were in place.

  • Curtain Arc – the semi circular arc that the dust curtains are attached to.

  • OEM – Original Equipment Manufacture (aka real aircraft part).

  • Plastic Arc Retainer – A piece of heavy duty plastic shaped as a curve (arc).

Major Differences Between Classic and Next Generation Throttle Quadrants

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There is little mistaking the tell-tale white-coloured handles and skirts of the Next Generation Throttle

The advent of high quality reproduction parts that marry with advanced avionics suites, such as ProSim-AR and Sim Avionics, has led many flight simulator enthusiasts to strive closer to Microsoft’s claim ‘as real as it gets’.

The availability of OEM parts formally used in classic airframes has never been greater, and many enthusiasts are purchasing various parts and converting them to flight simulator use.

The ‘holy grail’ of conversion has always been the Boeing throttle unit, and depending upon individual requirements, many older style throttle units have been retrofitted to appear very similar, if not near-identical, to their Next Generation counterparts.

This article will compare and contrast the major differences between the Boeing 737 classic throttle and the Next Generation throttle.  The word classic is usually used to refer to airframes belonging to the 200, 300, 400 and 500 series.  The Next Generation (NG) refers to the Boeing 600, 700, 800 and 900 series.

Boeing 727-100 throttle quadrant.  Although there are obvious differences in that the 727 has three engines, the overall design and appearance of the quadrant is very similar to its modern counterpart.  Image copyright to Keven Walchle

Historical Context

The throttle quadrant observed in a modern airliner has relatively old roots. 

The fore bearer of the Next Generation throttle was designed in the late 50's and early 60's and was initially used in the Boeing 707 airframe.  As aircraft types evolved, throttle design remained relatively static with similar-designed throttles being used in the Boeing 727, 717 and 737 series aircraft.

The B737-100 made its debut in April 1968, to be followed shortly by the 200 series with a slightly longer fuselage.  During the 1980’s Boeing released the classic series of airframes (300 through to 500 series). 

During this time, the technology altered little and the design of the throttle quadrant reflected the ability of Boeing to reuse existing technology with minimal alterations.  This principle of reuse can save a company millions of dollars in redesign and development costs.

This Goes With That (Compare and Contrast)

The Boeing 737-800 Next Generation is the airframe that many enthusiasts strive to duplicate in a flight simulator.  The reason for this two-fold.  First, the Next Generation is the most umbilicus aircraft flown today, and second, the availability of software that mimics the avionics suite in this aircraft.

However, Next Generation parts are difficult to find, and when found are expensive to procure.  Fortunately for the simulation community, a throttle will function correctly in flight simulator no matter what airframe the throttle originated.

Many of the nuances between a classic and Next Generation throttle quadrant are subtle, and for the most part only the more knowledgeable will notice.  

The more obvious highlights of the Next Generation are the white-coloured thrust lever shrouds, TOGA button assembly, détentes flaps arc, speedbrake lever knob, and the moulded white-coloured side panels and panniers of the lower part of the throttle unit.  Whilst it's possible to alter many of the attributes of a classic throttle to conform with those of an Next Generation, not every part can be easily transformed.  For example, the flaps détentes arc between the classic and Next Generation is very different in design and appearance, and cannot be altered.

TABLE 1: Overview to the main visual differences between the classic and Next Generation throttle quadrants (courtesy Karl Penrose who kindly allowed the use of photographs taken of his 600 series throttle).  Note that there may be other subtle differences, some visual and others in design/operation. 

The table doesn't address the center pedestal as pedestals vary greatly between airframes. 

Retrofit refers to the level of difficulty it is to make the classic throttle appear similar to the Next Generation. Yes meaning it is possible and no, for the most part, meaning it is not possible.

 

TABLE 1: an overview to the main visual differences between the classic and Next Generation throttle quadrants

 

1Erratum:  The trim wheels on the Next Generation are slightly smaller in circumference to those of the Classic series.

2  The words 'level of difficulty' is subjective; it depends on numerous factors such as experience and knowledge – neither of which is identical between individuals.

Important Point:

  • By far the most challenging hurdle during a Next Generation refit is the the alteration of the throttle lever shrouds and the TOGA button assembly.

Final Call

The differences between a classic and Next Generation throttles are largely cosmetic with some subtle design and operational differences.  Retrofitting a classic throttle to appear similar to a Next Generation throttle is possible.  However, there will be some things that probably won't be altered, such as the speedbrake lever handle, stab trim indicator tabs, side mouldings, panniers and flap détentes arc.  

This said, the ability to use an OEM throttle, no matter from which airframe, far supersedes any reproduction unit on the market.  OEM throttles are sturdy, robust and well-built.  Unless you do something particularly foolish, you won't damage an OEM throttle.

BELOW:  Two image galleries showing the various differences between the classic and Next Generation throttle quadrants.  Thanks to Karl Penrose who kindly allowed the use of photographs taken of his 600 series throttle.  To stop the slideshow, click the image and navigate by the numbered squares beneath the image.

Boeing 737 Classic Series Throttle Quadrant

 
 


Boeing 737 Next Generation Series Throttle Quadrant

 
 

  • Updated 21 June 2020.

Throttle Quadrant Rebuild - Evolution Has Led to Major Alterations

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oem 737-500 thrust levers

Two major changes to the simulator have occurred.  The first concerns the throttle quadrant and the second is the replacement of the trial Interface Master Module with a more permanent modular solution.  The changes will be documented in the near future after final testing is complete.

The throttle quadrant has been completely rebuilt from the ground up.  Although the outside may appear identical to the earlier quadrant, the rebuild has replaced nearly everything inside the quadrant and the end product is far more reliable than its predecessor.

The throttle unit, in its previous revision, worked well, but there were several matters which needed attention.  The automation and functionality was adequate, but could be improved upon.  There were also 'niggling' issues with how the clutch assembly operated - it was somewhat loose which caused several flow-on problems.

Initially, some minor improvements were to be made; however, one thing lead to another and as 'fate would have it' the throttle unit has been rebuilt from the bottom up.

Improvements

The improvements have primarily been to the automation, the autothrottle and the speedbrake system.  However, during the rebuild other functionality have been improved: the synchronised tracking movement of the thrust levers is now more consistent and reliable, and an updated system to operate the parking brake has also been devised.  This system replicates the system used in the real aircraft in which the toe brakes must be depressed before the parking lever can set or disengaged.

Furthermore, the potentiometers controlling the movement of the flaps and thrust levers have been replaced with string potentiometers which increases the throw of the potentiometer and improves accuracy.  The calibration of the flaps and speedbrake is now done within the system, removing the need for 'tricky' calibration in FSUIPC. 

In the previous throttle version there was an issue with the speedbrake not reliably engaging on landing.  This in part was caused by a motor that was not powerful enough to push the lever to the UP position with consistent reliability.  This motor has been replaced with a motor more suitable to the power requirement needed.  The speedbrake is mechanical, mimics the real counterpart in functionality, nd does not require software to operate.

This throttle conversion has maintained the advanced servo card and motor that was used to control the movement of the stab trim tabs (trim indicators); however, the motor that provides the power to rotate the trim wheels has been replaced with a more reliable motor with greater power and torque.  The replacement motor, in conjunction with three speed controller interface cards, have enabled the trim wheels to be rotated at four independent speeds.  This replicates the four speeds that the wheels rotate in the real 737 -800 aircraft.

Finally, the automotive fan-belt system/clutch system which was a chapter from the 'Dark Ages' has been replaced with two mechanical clutch assemblies that has been professionally designed to operate within the throttle unit - this will completely remove any of the 'niggles' with the previous clutch assembly becoming loose and the fan belt slipping.  Each thrust lever has a dedicated poly-clutch and separate high powered motor. 

A brief list of improvements and changes is listed below:

  • Next Generation skirt replaced with more accurate skirt (prototype);

  • Reproduction TO/GA buttons replaced with OEM square TO/GA buttons;

  • Fan belt driven clutch system replaced with slipper clutch system;

  • motors replaced that control lever movement and trim wheels;

  • 95% of wiring re-done to incorporate new interface modules;

  • Replacement interface alert system;

  • Flap potentiometers replaced by string potentiometers;

  • Speedbrake potentiometer replaced by linear potentiometer;

  • Thrust levers potentiometers replaced by dual string potentiometers;

  • Internal mechanism altered to stop noise of chain hitting throttle frame;

  • Thrust lever tracking movement accuracy improved;

  • Thrust reversers now have proportional thrust for each lever 1 and 2; and

  • The parking brake mechanism replaced with a more accurate system that reflects that used in the real aircraft

The conversion of the throttle quadrant has been a learning process, and the changes that have been done improve the unit's functionality and longevity - not too mention accuracy, far beyond what it was previously.

Dedicated Interface Modules

The throttle previously interfaced with the Interface Master Module (IMM).  The IMM was developed as a trial module to evaluate the modular concept.

The throttle quadrant will now directly interface with two dedicated modules called the Throttle Interface Module (TIM) and Throttle Communication Module (TCM).  Both of these modules contain only the interface cards, relays and other components required to operate the throttle and automation.  Additionally, the system incorporates a revised Interface Alert System which evolved from the original concept used in the IMM.

To read more concerning the various interface modules, a new website section has been produced named Interface Modules.  This section is found in the main menu tabs at the top of each page.

Flight Testing (March 2015)

The throttle and replacement interface modules are currently being evaluated and minor issues rectified.

Once testing is complete, the alterations undertaken during the rebuild process will be documented in separate posts and, to facilitate ease of searching, links will be added to the flight controls/throttle quadrant section.

It should be noted that the work done to rebuild the throttle was done with the help a friend, who has a through knowledge of electronics and robotics.

B737 Throttle Quadrant - Automated Thrust Lever Movement

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Autothrottle arming switch is a solenoid operated switch clearly identified on the main Instrument Panel (MCP).  The switch is linked to the IAS/MACH speed window (adjacent) and to two A/T disconnect buttons located either side of the throttle lever handles. cp flight pro mcp

In this final post dealing with the conversion of the 737-500 throttle quadrant. I will discuss the automation and movement of the throttle thrust levers and touch on some problems that occurred.  I will also briefly discuss the installation and use of potentiometers.  Part of this post will be repetitive as I briefly discussed automation in an earlier post.

Avoiding Confusion - Automation

To avoid confusion, automation refers only to the movement of the two throttle thrust levers in relation to the %N1 output.  These N1 limits and targets are provided by the Flight Management Computer (FMC) and normally are used by the Autopilot Flight Director System (AFDS) and the Auto Throttle (A/T) to maintain airspeed and/or thrust setting.  

Automation and Movement - Interface Cards

Automation is the use of CMD A or CMD B (autopilot) to control the %N1 outputs from the Autothrottle (logic), and motorization is the moving of the throttle levers in unison with %N1 output.  To achieve this seamlessly, two interface and one controller card are used.

Alpha Quadrant Cards (2):  Each  motor controller card has the automation logic programmed directly to the card (via propriety software).  One card controls Auto Pilot CMD A while the other card controls Autopilot CMD B.

Phidget Advanced Servo Card (2):  This card acts as an interface and bridge between the Alpha Quadrant cards and the flight simulator platform used.

The card does not provide movement for the throttle thrust levers; this is controlled by a Phidget Motor Controller card.

Leo Bodnar BUO 836 A Joystick Controller Card:  This card will register in Windows the movement of levers, buttons and switches on the TQ.  Calibration of this card is done first in Windows, then in Flight Simulator (FSX/P3D), FSUIPC or the avionics suite used; for example, ProSim737.

The interface cards are mounted forward of the MIP within the Throttle Interface Module (TIM) and are connected to the throttle unit by custom VGA straight-through cables and to the computer by a single USB cable.

Main Controller Cards

The controller card I have used is not a Phidget card but a specialist card often used in robotics (Alpha Quadrant card).  The software to program the card has been independently developed by a software engineer and does not utilize Phidgets.

The technology used in the controller card is very similar to that utilized by NASA to control their robotic landers used in the space industry.  The technology is also used to control robots used in the car industry and in other mass production streams.  One of the benefits of the card is that it utilizes a software chip (firmware) that can be easily upgraded, reprogrammed, or replaced.  

The Alpha Quadrant cards provide the logic to operate the throttle automation (the movement of the thrust levers) and act as a bridge between the two cards and the avionics suite.

Being able to program each card allows replication of real aircraft logic and systems.  Whenever possible, these systems and their logic have been faithfully reproduced.

oem throttle. toga switches clearly seen

CMD A/B Autopilot - Two Independent Systems

Most throttle units only use one motor controller card which controls either CMD A or CMD B; whichever autopilot you select is controlled by the same card.  

In the real aircraft to provide for redundancy, each auto pilot system is separate.  This redundancy has been duplicated by using two Alpha Quadrant controller cards, rather than a single card.  Each controller card has been independently programmed and wired to operate on a separate system.  Therefore, although only one CMD is operational at any one time, a completely separate second system is available if CMD A or B is selected on the MCP.

Synchronized or Independent Lever Motorization

Synchronization refers to whether the two throttle thrust levers, based upon separate engine %N1 outputs, move in unison with each other (together) or move independently.

In earlier Boeing aircraft, such as the 707, 727 and 737 classics, the levers were roughly synchronized; however, the Next Generation has as a computer-operated fuel control system which can minutely adjust the %N1 of each engine.  This advanced fuel management can be observed in a real aircraft whereby each throttle lever creeps forward or aft independent of the other lever.

Programming flight simulator to read separate %N1 outputs for each engine, and then extrapolating the data to allow two motors to move the throttle levers independently is possible; however, the outputs are often inaccurate (for varying reasons).  This inaccuracy can often be observed on reproduction throttle units that exhibit a gap between lever one and lever two when automating %N1 outputs.  

It was decided to maintain the older system and have both levers synchronized.  Although this is not replicating the Next Generation system, it does make calibration easier.  If in the future incremental thrust lever movement is required, it’s a matter of adding another 12 Volt motor to the front of the throttle bulkhead to power the second thrust lever.  

Autothrottle activation will advance both thrust levers in unison to the fmc calculated %N1 output

Be aware that although both thrust levers are synchronized, the throttle handles may still show a slight difference in position in relation to each other.  This is caused by the varying tension that needs to be maintained on the fan belt connecting the 12 Volt motor to the mechanical system beneath the thrust levers.

Another aspect to note is that the position of the thrust levers during automation is arbitrary and is a visual representation of the %N1 output; it may or may not reflect the exact position on the throttle arc that the thrust lever would be placed if moved manually (by hand with Autothrottle turned off).  

Although the throttle is automated, manual override (moving the thrust levers by hand) is possible at any time, provided the override is within the constraints of the aircraft logic (programmed into the Alpha Quadrant card), and that provided by the flight avionics (ProSim737).  

Power Requirements and Mechanics

To provide the power to move the throttle thrust levers, a 12 Volt motor previously used to power electric automobile windows, is mounted forward of the throttle bulkhead (see image at bottom of post).  Connected to the motor's pulley is a fan belt that connects to the main pulley located beneath the thrust levers.  To enable the thrust levers to move in unison, a slip clutch, which is part of the main pulley assembly, is used.  

Captain-side TO/GA button is clearly seen below lever handles.  The button at the end of the handle is the Autothrottle disconnect button

ProSim737 Limitations - TO/GA and Auto Throttle Override

Unfortunately, concerning automation the ProSim737 is deficient in two areas: TO/GA and A/T Override.

(A)  TO/GA

In the real aircraft, the flight crew advances the thrust levers to power 40%N1 (or to whatever the airline policy dictates), allows the engines to spool, and then pushes the TO/GA button/s.  Pressing TO/GA causes the throttle to go on-line and to be controlled by the AFDS logic.  The throttle levers then advance automatically to whatever %N1 the logic deems appropriate based on takeoff calculations.

As at the time of writing. If you're using ProSim737, this will NOT occur.  Rather, you will observe the thrust levers retard before they advance (assuming you have moved the thrust levers to %40 N1).  The reason for this is nothing to do with how the throttle is calibrated, FSUIPC or anything else.  ProSim737 software controls the %N1 outputs for the automation of the thrust levers and the developer of the software has not fine-tuned the calibration in the software to take into account real-world avionics logic.  This thread located on the ProSim737 forum provides additional information. 

I have not tested Sim Avionics, but have been told this issue doesn't occur in their avionics suite.

There are two workarounds:  Engage TO/GA from idle (hardly realistic) or push the thrust levers to around 80% N1, allow the engines to spool, then push TO/GA.  Anything less that around 80% N1 will cause the thrust levers to retard before advancing.

Latest ProSim737 release (V133)

The latest version of ProSim737 (V-133) has provided improvement to the above issue.  Throttles can now be advanced to ~60% N1 and TOGA engaged without the throttle levers retarding.  This is possible ONLY if you calibrate the throttle levers within ProSim and allow ProSim to control the throttle output logic.  if you calibrate within FSUIPC then the same issue will apply.

According to ProSim developers, this issue is probably related to the calibration of the ProSim servo output. When you press TO/GA, the current N1 is taken and calculated back to a throttle percentage. This throttle percentage, when combined with the servo calibration data from ProSim results in a servo output. The servo calibration at the moment only has 2 calibration points, which are 0 and 100%. This results in a linear behavior between the two points, while depending on the construction of the throttle, the relationship might be non-linear. This would require a multi point calibration which is hard to do at the moment, because a throttle does not have exact readouts of the current position, so it will be hard to calibrate a 50% point.

This may need improvement in the code to auto calibrate the throttle system.

It's hoped that future release of ProSim737 will rectify this issue.

(B) Autothrottle Manual Override

In the real aircraft, manual override is available to a flight crew and the thrust levers can be retarded with the Autothrottle engaged.  When the flight crew release pressure on the thrust levers the Autothrottle will take control again and return the thrust levers to the appropriate position on the throttle arc dependent upon the speed indicated in the speed window of the MCP.

ProSim737 will not temporarily disconnect (manual override) the Autothrottle.  

At the time of writing, there is no workaround to solve this.

Potentiometers

There are many types of potentiometers; the two types most commonly used in flight simulation are the linear and rotary types. Linear potentiometers are inexpensive, often have a +- percentage variance, are compact, have a minimal throw depending upon the size of the device, and are not immune to contaminates building up on their carbon track. 

The last point is worth mentioning, as it is wrongly assumed that a potentiometer will remain correctly calibrated for the life of the unit.  General wear and tear, dust, and other debris will accumulate on the potentiometer; any of which may cause calibration and accuracy problems.  Keeping the potentiometers free of dust is important.

Rotary potentiometers (which may have a string attached) are very accurate, are in a sealed case and have very minimum chance of contamination. They are also made too exacting standards, are larger in size, and are expensive.

To read further about potentiometers

QAMP secured to base of throttle unit.  Thumb screws are visible on each corner of the plate.  A possible add on modification to reduce the risk of dust contamination to the potentiometers is a plastic cover that fits over the plate (a lunch box)

Calibration of Potentiometers

The main method of calibrating the position of the thrust levers is by calibrating the potentiometer in Windows, then in FSX followed by fine tuning in FSUIPC (if needed).  

At the moment I am using linear potentiometers; therefore, at some stage cleaning or replacement may be required.   The 737 throttle quadrant is not cavernous and only certain sized potentiometers will fit into the unit; this combined with other parts and wiring means that the potentiometers are often inaccessible without removing other components.  

To allow speedier access to the potentiometers, a Quick Assess Mounting Plate was designed.

quick access mounting plate (QAMP). four linear potentiometers are mounted to the plate. Two grub screws secure the plate to the throttle chassis

Quick Access Mounting Plate (QAMP)

The potentiometers are mounted directly onto a custom-made aluminum plate that is attached to the inside of the throttle unit by solid thumb screws.   To access the plate, the side inspection cover of the throttle is removed (a few screws) followed by turning the thumb screws on the access plate.  This releases the plate.

A similar plate has been designed and constructed for use with the stand-by potentiometer that controls the flaps.  A more detailed picture of the QAMP can be seen here..

Below is a video showing the movement of the thrust levers with the autothrottle engaged recorded during a test flight. 

 
 

Teething Issues with the Throttle Conversion

It was envisaged that more problems would have surfaced than have occurred.  The major issues are outlined below:

(A) Trim Wheels

An early problem encountered was that the trim wheels when engaging generated considerable noise.  After checking through the system, it was discovered that the two-speed rotation of the trim wheels were causing the two nuts that hold each of the trim wheels in place to become loose.  This in turn caused the trim wheels to wobble  slightly generating undue noise.  

Solution:

Tighten the two nuts at the end of the rod that holds the two trim wheels in place.

(B) Flaps 5 Not Engaging

The problem with the flaps 5 micro-button has been discussed in an earlier post.  To summarize, when you moved the flaps lever to flaps 5 the correct flaps were not selected on the aircraft or registered on the PoKeys 55 interface card.  Several hours were spent checking connections, micro-buttons, wiring and the custom VGA cables that connect the flaps section of the quadrant to the appropiate interface module; the problem could not be discovered.  

Solution:

One of the two Belkin powered hubs located within the IMM had been replaced with another powered unit.  It appears the problem was that the replacement hub had too low a voltage, as a replacement with a higher voltage solved the problem.

(C) Throttle Thrust Levers Not Synchronizing (A/T on)

The two thrust levers of the quadrant did not synchronize when the Auto Throttle (A/T) was engaged; one lever would always be ahead or behind of the other.  At other times they would split apart (do the splits) when A/T was engaged.  

Solution:

The problem was easily solved by altering the tension on the slip clutch nut.  When the nut was  tightened, both levers moved together as one unit.  The secret was finding the appropriate torque.

(D) Throttle Thrust Levers Difficult To Move in Manual Mode (A/T Off)

The ability to move the thrust levers in manual mode (Autothrottle turned off) was not fluid and the levers occasionally snagged or were sticky when trying to move them.  

The fan belt is barely visible linking the pulley of the motor to the main pulley inside the quadrant

This is caused by the fan belt not moving smoothly through the groove of the pulley wheel.   The Autothrottle when engaged overrides any stickiness due to the power and torque of the Auto Throttle motor.

Solution:

Unfortunately, there isn’t a lot you can do to rectify this issue as it’s a by-product of using a mechanical system in which the fan belt is central to the consistent operation of the unit.  

The conundrum is that if you tighten the fan belt too much you will be unable to manually move the thrust levers as they will be exceptionally stiff and difficult to move (as you are pushing against the tension of the fan belt); however, if you loosen the fan belt too much, although the levers will move fluidly by hand, the fan belt may not have enough tension to move the levers when Auto throttle is engaged.  It’s a matter of compromise; selecting an appropriate in-between tension to allow acceptable manual and Autothrottle operation.

A more reliable method is to use a small gearbox, a simple slip clutch and a coupler to connect to the spur gear.  Another option is to use an electrical system.

Further thought needs to be done in this area before a decision is made to replace the fan belt system.  If a new system is incorporated, the change-out will be documented in a future post.

Conclusion

Despite some of the shortcomings to this conversion, in particular the mechanical fan belt system, the throttle unit shows a marked improvement on the earlier 300 series conversion. 

Since the project began there has been three throttle conversions, and wth each conversion has built upon knowledge learnt from earlier conversions.  Initially there was the 737-300 conversion in 2012, which was converted in a rudimentary way and only operated in manual mode.  This was followed by the conversion of the 737-500 throttle in 2016.  This throttle was then rebuilt and upgraded in 2017.

Further Information

  • A summary of the articles that address the conversion of the 737-500 series throttle quadrant conversion, and the rebuild and update can be found in Flight Controls/Throttle Quadrant.

Acronyms and Glossary

  • AFDS - Autopilot Flight Director system

  • A/T – Autothrottle

  • CMD A/B - Autopilot on/off for system A or system B

  • Flight Avionics Software - Sim Avionics, ProSim737 or similar

  • FMC - Flight Management Computer

  • MCP - Main Control Panel

  • QAMP – Quick Access Mounting Plate

  • Throttle Arc – The arc of the thrust levers from the end of the blocks to fully forward.  The term refers to the curved piece of aluminum that the throttle levers are moved along

  • TO/GA - Takeoff Go-around switch

  • %N1 -  Very simply explained, %N1 is throttle demand and as N1 (and N2) spin at absurdly high speeds, it is easier to simply reference a percentage and display that to the crew. It's much easier for our brains to interpret a value on a scale of 0-100% rather than tens of thousands of RPM 

B737 Throttle Quadrant - Trim Wheels and Trim Indicator Tabs

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Captain-side trim wheel and trim tab indicator.  I was fortunate that the throttle unit I aquired retained its light plates in excellent condition.  It's not uncommon to find that the light plates are faded, scratched and cracked from removal of the unit from the aircraft

This post, the third last concerning the throttle quadrant conversion, will discuss the spinning of the trim wheels and movement of the trim tab indicators; both integral components of the throttle quadrant.  For a list of articles about the conversion of the throttle quadrant, see the bottom of this page.

1:  TRIM WHEELS

The trim wheels were implemented by Boeing in the mid 1950’s with the introduction of the Boeing 707 aircraft and been a part of the flight deck ever since.  The main reason Boeing has continued the use of this system in contrast with other manufacturer, who have removed the spinning trim wheels is redundancy.  Boeing believes that the flight crew should have the ability to manually alter trim should a number of cascading failures occur.

Whatever the reason for Boeing continuing with this older style technology, many flight crews have learnt to “hate “ the spinning trim wheels.  They are noisy and distracting, not to mention dangerous if a flight crew accidentally leaves the handle in the extended position; there is a reason that they are called “knee knockers”.  

Many virtual pilots are accustomed to using manual trim when flying a Cessna or a small twin such as the King Air.  In such aircraft altering trim by hand is straightforward and a necessary part of trimming the aircraft.  However, a jet such as the B737 it is a tad different; to alter the trim by hand would require the flight crew to manually rotate the trim wheels several dozen times to notice any appreciable result in trim.  As such, the electric trim switches on the yokes are mainly used to alter trim.

Motors, Interface Cards and Speed of Trim Wheel

The power to spin the trim wheels comes from two 12 Volt DC pump motors installed within the throttle unit.  A Phidget High Current AC Controller card is used to interface the trim wheels to the flight avionics software (proSim737). The cards are located in the Interface Master Module (IMM) and connected to the throttle unit by customised VGA cables.

The trim wheels can spin at two speeds.  The autopilot producing a different speed to that of manual trim (no automation selected).  A Phidget card is used to control the variability, with each of the two channels programmed to a different speed.  To alter the actual revolutions of the trim wheel, each channel is accessible directly from within the ProSim737 software configuration.   

To allow the trim system to be used by CMD A and/or CMD B, a second card is installed to ensure duplicity.  

Correct Timing

The trim wheels have white longitudinal line painted on each trim wheel.  This line serves two purposes: as a visual reference when the trims wheels are spinning, and to determine the number of revolutions per second during calibration.  To ascertain the correct number of wheel revolutions per second, a digital tachometer is used in the same way a mechanic would tune an older style motor vehicle.

Out of interest, in manual trim, 250 revolutions of the trim wheels are necessary to move the trim tab indicators from full up to full down.

Two Speed or Four ?

The B737 has four different trim revolution speeds, each speed dependent upon the level of automation used and the radio altitude the aircraft is above the ground.

Although it is possible to program this logic into the Alpha Quadrant cards and bypass ProSim737 software entirely (closed system), it was decided not to as the difference in two of the four speeds is marginal and probably unnoticeable.  Further, the level of complexity increases somewhat programming four speeds. 

Autopilot mode rotates the trim wheels at a faster rate than when in manual trim.

Trim wheel removed showing heavy duty spline shaft

Trim Wheel Braking

The real 737 incorporates a braking mechanism on the trim wheels that inhibits wheel movement when there is no input received to the system from either the auto pilot or electric trim switches. The brake operates by electromagnetic radiation and is always on, being released when an input is received.  

An unsuccessful attempt was made to replicate this using two military specification high torque brake motors.   The motors incorporate a brake mechanism, but the torque was so high and the breaking potential so great, that when the brake was reengaging/disengaging there was a loud thud that could not be ignored.  Further, the motor became very hot when the brake system was engaged and vibrated excessively due to its high power rating.

At the time, a lower torque motor could not be procured and a decision was made to use the 12 volt pump motors.  Therefore; the trim wheels take an extra second or so to spin down – not a major imposition and barely noticeable when flying the aircraft..

Deactivating Trim Wheel Spinning

Most of my virtual flying is at night and noisy and vibrating trim wheels can easily aggravate others in the house attempting to sleep.  To allow easy disconnection of the trim wheels, I have configured the right side trim stabilizer toggle to cut the power to the trim wheels.  Although not authentic, sometimes minor alterations need to be made to a system to make it more user friendly.

2:  TRIM TAB INDICATOR MOVEMENT

The trim tab indicators are used as a visual reference to indicate to the flight crew the trim of the aircraft.  The trim and subsequent movement of the indicator tabs are activated either by depressing the electric trim switch on the yoke or by turning the trim wheels by hand.

Phidget Card

A Phidget Motor Controller Advanced Servo card and servo is used to control the movement of the two trim tab indicators, while the logic to activate the servo is directly from the flight avionics software.  The speed that the trim tabs move is set through ProSim737 (trim speed).

Aluminum tab connected to servo.  Servo is mounted behind aluminium plate.  You can just make out the screw wire between the servo and the tab

Hardware Modifications

To allow the servo to connect directly to the trim tab indicators, a small tab of aluminium was welded to the main trim tab shaft.  A thin screw wire was then connected from the servo to the tab to allow nay movement of the trim tab to be registered by the servo. 

Determining Accuracy

There is little point in implementing movement of the trim tab indicators if a high level of accuracy is not possible; therefore, it’s important that that the position of the tabs matches that of the flight avionics software and virtual aircraft.  To ensure positional accuracy and maintain repeatability the servo was calibrated throughout its range of movement and checked against the “virtual trim tab strip” that can be placed on the EICAS screen within the ProSim737 software.  

The short video below shows the smoothness in movement of the trim tab indicators.  You will note the TQ vibrates somewhat.  This is because I have yet to secure it to the platform.

 
 

B737 Throttle Quadrant - Flaps UP to 40; Conversion and Use

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This post examines the flaps lever on the refurbished B737 throttle and how it was converted to flight simulator use..

Flaps are used to slow the aircraft by creating drag, and to apply positive lift during takeoff.  The flaps lever is located on the First Officer’s side of the throttle quadrant. 

Subsequent movement of the flaps lever is indicated by illumination of the Le Flaps Transit and Le Flaps EXT lights located on the Main Instrument Panel (MIP), movement of a needle in the flaps gauge, a change of indication in the Primary Flight Display (PFD) and illumination of the Leading Edge Device (LED) panel located on the aft overhead panel. 

There are other less obvious indicators, but this is not the direction of his post.

The flaps lever is an integral part of the throttle unit.  Ensuring it operates correctly and with accuracy is important.

oem 737 throttle showing flaps arc and takeoff cg%mac

Safety Features

Newcomers to an OEM throttle quadrant are often surprised at how difficult it is to manipulate the flaps lever; it isn't a simple pull or push of a lever - there is a reason for this. 

When flaps are extended, especially at slow air speeds the flight dynamics of the aircraft are altered.  To protect against accidental flap extension, Boeing has designed the flaps lever so that a flight crew has to physically lift the lever before moving the lever to the required flap setting.  

Further safety has been designed into the system by having flaps 1 and flaps 15 guarded by a flaps gate.  The gate prevents straight-through movement of the flaps lever beyond flaps 1 and 15.  The  pilot must actually lift, push and drag the lever through the gate to the next setting.

It takes a short time to become accustomed to how to move the lever for smooth operation.

Traditional Approach used in Flaps Conversion

In most throttle conversions, a single potentiometer is used and the flaps are calibrated directly through FSUPIC.  A linear rod is attached to the potentiometer and then to the lower end of the flaps lever.  When the flaps lever is moved, the rod is moved forward or aft causing the potentiometer to turn to a defined and pre-calibrated position.  The analogue movement of the rod is converted to a digital signal that can be read by Flight Simulator.

In such a conversion, it’s important to ensure that the physical position of the flaps lever matches the flaps position used in Flight Simulator and in the flaps gauge.  It’s also vital that flaps are calibrated to ensure accurate operation.

The benefits of using this traditional method are that it’s “tried and true”, inexpensive and relatively easy to implement.  Calibration is the major key; however, using FSUIPC can be troublesome and time consuming, although once calibrated everything should operate reasonably well.  

Potentiometers - Accuracy and Longevity

Potentiometers came in a variety of sizes with differing throw values.  A throw is the length of movement that a potentiometer will allow a linear rod to move.  The larger the potentiometer the more throw allowed.  The potentiometer for the flaps must fit within the throttle unit beneath the flaps mechanism in a relatively small space.  Unfortunately, with Boeing 737 late model throttle’s there is minimal room to allow a larger than 60mm potentiometer to be installed.  Using a 60 mm potentiometer means that the device has a minimal throw.

This throw, if lucky, can be stretched to cater from flaps 0 to flaps 40, but only after facetiously calibrating with FSUPIC.  More often than not,  the throw will only reach flaps 1 or flaps 30.  Often this lack of throw goes unnoticed and many virtual pilots select flaps 40 believing they actually have flaps 40, but in reality it is flaps 30.

Longevity is another more minor issue when using potentiometers.  Most potentiometers have a +- tolerance during manufacture, are made cheaply and depending upon the type selected are open to contamination from dust and debris.  Dust on a potentimeter can affect the accurancy of the unit. At the very least, maintenance is required if the potentiometer is located in a dusty area.

Several Ways to Skin a Cat.....

To solve these potential problems two methods were assessed.  The first was using two micro- buttons at each end of the linear rod that connects the flaps lever with the potentiometer.  These buttons can be assigned directly with FSUPIC to flaps UP and flaps 40.  This theoretically would solve the shortness of throw experienced with traditional conversion and calibration.  Flaps UP and 40 are controlled by micro-buttons and everything in-between is calibrated within FSUPIC.

Working through an issue with the Flaps 5 micro button, custom VGA cable and PoKey card. it's not all fun.  Chasing problems can be frustrating and very time consuming

Micro-buttons

The second method is to replace the potentiometer with micro-buttons; thereby,  rectifying the issue of minimal throw.  Replacement will also alleviate the chance of a potentiometer being inaccurate, remove any chance of contamination, and also remove the tedious task of calibrating flaps in FSUIPC.   

The use of micro-buttons to control flaps movement is relatively novel, but the potential benefits of implementing this into the throttle unit could not be overlooked; therefore, it was decided to use this method.

Problems with Micro-buttons - Design of Lower Flaps Arc Plate (LFAP)

The first initial problem encountered is that micro-buttons are small, delicate and can be easily damaged if mounted directly onto the metal flaps arc.  Manipulating the flaps lever requires considerable pressure to pull, drag and drop the lever into the correct flaps detent position. Clearly, mounting the buttons on top of the metal flaps arc for direct contact with the flaps lever was not feasible.

After much thought, it was decided to fabricate from aluminum, a plate that replicated the arc that the flaps lever moves over.  This plate has been called the Lower Flaps Arc Plate (LFAP).  The micro-buttons were then strategically mounted to the plate, each buttons’ position corresponding to a flap position.  The LFAP with the mounted buttons was then mounted directly beneath the existing flap arc plate. 

Design Considerations

Before implementing a new design, considerable thought must be taken to potential problems that may arise from the design.  In the case of using micro-buttons the issue was connectivity and the possibility of a damaged or faulty button.  The LFAP can be accessed relatively easily by removing the First Officer's side panel which allows access to the plate from behind the trim wheel.

Half-moon Provides Accuracy, Reliability and Repeatability

To enable the micro-buttons to be triggered by the flaps lever, a half-moon piece of aluminum was fabricated using the same dimensions of the lower portion of the flaps lever.  One end of the "half-moon" was  curve-shaped pointing downwards. The "half-moon" was then screwed to the lower section of the flaps lever handle   

LEFT:  Rough initial sketch of half-moon showing relationship to flaps arc and micro-buttons.

When the flaps lever is dropped into a flaps detent position, the curved side touches and depresses the micro-button mounted on the lower flaps arc plate.  When the flaps lever is moved to another flaps setting, the lever is first lifted breaking contact with the button, moved to the next setting and dropped into the detent position triggering the next button and so forth.

Interface Card

A standard PoKeys 55 interface card was used to connect the outputs from the buttons to the avionics suite software.  ProSim737 software allows easy interfacing by allowing direct connection of a button to a specific flap position.  If ProSim737 is not used and the chosen avionics suite does not support direct connection, FSUIPC can be used to assign individual buttons to flap positions.  The PoKeys card is installed in the Interface Master Module (IMM).

Advantages of Micro-buttons - It's Worth The Effort...

The benefits of using micro-buttons cannot be underestimated. 

  • 100 % accuracy of flap movement from flaps UP to flaps 40 at all times.

  • No calibration required using FSUIPC.

  • Non-reliance on FSUIPC software as the installation is mechanical.

  • Very easy configuration of flaps UP through flaps 40 using ProSim737 software configuration.

  • Removal of the potentiometer and possible inaccuracy caused by +- variation.

  • No concern regarding possible contamination of the potentiometers.

  • Enhanced reliability of operation with no maintenance required.

  • Easy removal of the Lower Flaps Arc Plate to facilitate button replacement.

Back-up Potentiometer System

Although the use of micro-buttons is successful, I still have a potentiometer installed that can be used to operate the flaps.  The reason for installing the potentiometer was in case the micro-buttons did not work correctly; it would save time installing a replacement system.  To change from buttons to the potentiometer is as easy as disconnecting one quick release connector and reconnecting it to another.

qamp. the quick access mounting plate enablse 4 linear potentiometers to be mounted in one location. the qamp is located in throttle unit

Quick Access Mounting Plate (QAMP)

The potentiometer is mounted directly onto a custom-made aluminum plate that is attached to the inside of the throttle unit by solid thumb screws. 

The reason for the plate and screws was easy access should the potentiometer need to be cleaned or be replaced. 

To access the potentiometer requires the side inspection plate of the throttle be removed (a few screws) and then removal of the thumb screws on the access plate that allows the potentiometer to be dropped from its bracket.

Unfortunately, I failed to photograph the flaps QRMP before installation; however, its design is similar to all quick release plates used within the throttle unit.  The plates are made from aluminium and are attached to the throttle unit by thumb screws rather than nuts and bolts.  This allows for easier and faster change out if necessary.  The above image shows the QRMP for the throttle levers - the flaps QRMP is far smaller and thinner.

Troubleshooting

During testing a problem was observed with the micro-button for flaps 5.  For an unknown reason flaps 5 would not register correctly on the PoKeys 55 card.  After several hours troubleshooting the buttons and wiring, it was determined that the PoKeys card must have a damaged circuit or connection where they flaps 5 wire was installed to the card.

The problem turned out not to be the PoKeys card, but the Belkin USB hub installed to the Interface Master Module (IMM).  I had replaced the first hub (which I damaged) with another hub that had a lower voltage.  For some reason this lower voltage was not enough to allow operation of all the functions running from the hub. 

After replacing the hub with a higher voltage device, the issue with the flaps was immediately rectified.  Of course, this was after I spent literally hours troubleshooting flaps 5!  As stated earlier, teething issues on a new design can be frustratingly time consuming...

Video

I decided to make a short video that explains the button set-up a little better.  In the video you can clearly see the flaps arc, half-moon pencil and the micro-buttons.  The video is not the best quality as it was hand held in dim light after I removed the F/O side inspection plate of the throttle quadrant.  It's difficult if not impossible to setup a tripod in the flight deck once the throttle unit is bolted to the platform.

 

737 throttle flap arc buttons

 

Acronyms and Glossary

  • Flaps Arc – A curved piece of aluminum positioned directly beneath the flaps lever and corresponds to the curvature of the light plate.

  • Lower Flaps Arc Plate (LFAP) - A curved piece of aluminium that is the same size as the flaps arc and is mounted directly beneath the flaps arc.

  • Half-Moon Pencil – a custom fabricated piece of aluminum with a curved edge at one end.  Used to depress micro-buttons on flaps arc as flaps lever is moved..

  • OEM - Original Equipment Manufacturer.

  • Quick Access Mounting Plate QAMP – Quick Access Mounting Plate for the potentiometer that is a redundancy system for flaps movement.

  • Avionics Suite - Software that interacts with Flight Simulator to control avionics, gauges, etc - ProSim737, Sim Avionics, Project Magenta, etc.

Update

on 2014-02-12 02:13 by FLAPS 2 APPROACH

flaps half-moon

Several individuals have contacted me asking for a picture of the half moon, that is roughly sketched in the main post.  During a recent upgrade, the side panel and trim wheel were removed so I took the opportunity to take a photograph of the half-moon.

The half moon is secured to the lower section of the flaps lever by a screw, with the lower curved side facing downwards towards where the micro-buttons are positioned. The half-moon moves in unison with the flaps lever (when moved) and the curved section triggers micro-buttons as it passes over the button.  The micro-buttons are positioned at the correct position that relate to a specific flap detente.

Update

on 2019-09-09 07:29 by FLAPS 2 APPROACH

FLAPS OVERHAUL (LATE 2018/2019)

The mechanism used to convert the flaps on the throttle quadrant has been overhauled and replaced.  The method described in the above article worked well, however, a number of problems developed that were only noticeable after continual use.

Installing the ACE Yoke & 737-300 Throttle Quadrant

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ace engineering 737 yoke

ACE Yoke & Column

Now that the seats are attached, it’s time to secure the ACE yoke to the Captain side of the flight deck and then secure the throttle quadrant and center pedestal to the floor. 

Attaching the ACE yoke is straightforward; measure correctly against the MIP the spacing as per the Boeing specifications and attach with four screws – presto!

Throttle Quadrant

Ace engineering 737 yoke and column

I am hesitate to secure the throttle quadrant to the floor until I am very sure that the wiring is correct and everything functions.

Throttle Quadrant Does Not Sit Flush

The throttle quadrant does not sit flush with the MIP, the later having an angled front while the quadrant is a straight 90 degree angle.  I want to fabricate two angled side walls to cover this open space so you cannot see the wiring at the front of the quadrant.  I'll fabricate these panels probably from Perspex or MDF wood and paint in Boeing grey or stark white.  They will be screwed in place and be easily removed for wire maintenance (if necessary)

oem weber seats, 737-300 throttle quadrant and two bay center pedestal

I also want to determine how much the throttle moves when the trim wheels rotate; this will determine how and where I secure the throttle quadrant to the floor structure. 

Maintenance

Everything may be functioning on the throttle quadrant now, but in 12 months time it may be different. Maintenance is an ongoing task with anything that moves; therefore, it is important to enable easy access to wiring, etc. At some point the throttle quadrant may have to be removed from the platform, and the method used to secure the quadrant must facilitate easy removal.

Slowly Taking Shape

It's has taken some time, but the simulator is now beginning to look like a simulator rather than a room full of aviation junk.

Sticky Autothrottle Button - Repaired

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oem autothrottle button. note the circular circlip

I noticed soon after the throttle quadrant arrived that the engine number one auto throttle button was a bit sticky.  Depressing the button, it would stay pressed in for a few seconds even though pressure had been released.  The autothrottle buttons are one-way buttons meaning that they are click buttons.  It’s probable that after many hours of service, sweat, dead skin cells and dirt has built up on the inner button behind the spring mechanism; a friend suggested that DNA analysis of the built up debris would probably provide a list of suspect pilots!

Whilst the button was still in place, I attempted to loosen the built up material using a can of pressurized electronic cleaner fluid.  The fluid, I hoped would dislodge any loose material before evaporating.  Unfortunately, this didn’t work in the long run, although once lubricated with the evaporate solvent, the button operated correctly for a short time.

oem autothrottle button removed

Circlip

The button is held in place within the throttle handle by a ½ inch circlip.  Beneath the circlip and button there is a spring mechanism that pushes the button out after being depressed.  Using a pair of circlip pliers, I very carefully removed the circlip making sure that the spring mechanism of the circlip didn’t propel my button out the window and into the garden! 

With the circlip removed, the inner portion of the throttle handle slides out revealing the button and attached wiring.  The button is a modular design (shaped to fit inside the throttle handle) and unfortunately cannot be disassembled further, Therefore, I reassembled the button and sprayed a small amount of silicone spray around the button, allowing the silicone solution to penetrate around the the edge of the button. 

The silicon lubricant (which is non conductive, so there is no issue with power shorting) seems to have solved the problem as the button no longer sticks, however, this is only an interim solution.  I'll search for a replacement button module.  Sometimes the most simple solution will fix your problem.

No doubt I can purchase a new replacement from Boeing for err $800.00....  I think not.  Eventually I'll find a disused button module in my travels.  

Throttle Teething & Calibration Issues - It Was Expected

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oem 737-300 throttle quadrant

The throttle quadrant works well and I’m pleased with the result; however, as anticipated there are a few minor teething issues that require fixing.  There is a background humming noise, The engine one autothrottle switch is sticky, and there are some minor issues with the calibration of the throttle reversers and deployment of the speed brake. 

Background Humming Noise

When the phidget software is turned on with FSX there is an annoying background hum.  Initially, I thought this background hum to be the low frequency AC noise, but then realized that everything is DC – so there shouldn’t be any noise.  The cause of the hum is probably related to either of the following issues:

  • When the phidget software is turned on it’s activating power to the servo motor to deploy the speed brakes.  The servo motor is ready and waiting for a command, but as there is no command for movement and the servo motor has power running to it, it’s humming.  If this is the reason, then the installation of the Phidget 004 card will solve this issue. 

A Phidget 004 card has four relays which allow for three situations – on, off and always on.  When connected, the relays will tell the servo motor to switch off“until activated by movement of the speed brake.

  • The power to the throttle quadrant is from a 400 watt computer power source and a bench-top voltage reducing board).  I’ve been told that because all the power requirements are coming from a singular source, then this maybe a cause of noise.  The easiest method to solve this is to use two or three independent power sources.

Speed Brake Calibration - Auto Deployment of Handle

Calibration is always an issue when simulating a complex piece of machinery.  Calibration must take into account the various positions and operational requirements of the speed brake.  The speed brake must be recognised by the flight software in the following positions: off, armed and part/full detent.  It must also be configured to automatically activate (deploy) upon flare and touch down when the landing wheels touch the ground. 

The Boeing Operations Manual states: the thrust reverser can be deployed when either radio altimeter senses less than 10 feet altitude, or when the air/ground safety sensor is in ground mode.  Movement of the reverse thrust levers is mechanically restricted until forward thrust levers are in idle position.

Once touch down in achieved, the mechanical speed brake arm on the throttle quadrant will move automatically to the deployment position (full detent).  This is done by programming a squat switch.  A squat switch is standard on/off relay that tells the brake to either deploy or remain in the non deployment position.

Squat Switch & FSUIPC Programming

To program a squat switch I used a Phidget 0/0/4 card and programmed the F2Phidgets software to read squat switch in the interface.

To ensure that the speed brake was calibrated to FSX correctly I used FSUIPC.  One important aspect of the calibration is to ensure that the speed brake handle matches, more or less, the same movement of the virtual speed brake handle.  To check this you must open the throttle in FSX and observe the virtual movement of the handle while manipulating the real handle.

Using FSUIPC, open the Axis Assignment tab and move the speedbrake handle checking that the arm and detent positions are correct.  Select send to FSUIPC and tick (check) the spoilers in the drop down box.  Finally save the adjustments.

If you have not done so already, it's a good idea to have a FSUIPC profile set up to ensure that your changes are saved to specific aircraft.  For example my FSUIPC profile is called 737 Project.

Reversers

Once a Phidget 0/0/4 card is installed and the card relays calibrated appropriately to the speedbrake, it’s hoped that the calibration of engine 1 and engine 2 reversers through detent position 1 and 2 will be straightforward.

After consulting with others and solving these issues, I'll post an update to this thread (here).  Perhaps the information may benefit someone else doing a similar throttle retrofit.

Update

on 2014-12-23 12:50 by FLAPS 2 APPROACH

The hum is now gone.  The reason was straightforward; there was no commands being issued to the servo motor, so the motor was making a noise (this continual power to the motor eventually lead to its failure).  Once a command was directed to the motor, the noise disappeared.  To stop the motor from being turned on when there was not a command; a phidget relay was connected (on/off).  When the command is issued, the phidget relay opens and when the command is rescinded the relay closes and power to the motor is stopped. 

Reverse Thrust Levers

This also was relatively straightforward to solve. 

My problem lay in the fact that I was trying to program the reverse thrust levers to read three power settings (three detents) as in the real 737 aircraft.  The first detent/notch on the reverse lever opens the clam shells/buckets to redirect air, the second detent/notch provides 50% idle thrust and the third detent/notch applies full reverse thrust. 

The third position is rarely used as it can easily ingest foreign bodies into the engines from a contaminated runway causing engine damage - the exception being in very wet and/or snow conditions, when it is regularly used.

Unfortunately, programming the reverse thrust levers like this is not possible as flight simulator does not have the appropriate logic. 

Using FSUIPC to assign buttons & offsets

Once the problem was understood (with a little help from a real-world 737 pilot and another simmer), FSUIPC was used to program individual thrust to engine 1 and engine 2.  In FSUIPC, you assign a button to each of the reverse thrust levers, and then assign a flight simulation command (throttle set 1 and throttle set 2).  An offset parameter is required for each throttle which is -16384 / 0.  The repeat box must also be checked/ticked.

Real World Throttle Nuisances – they had me baffled for a time

One thing that baffled me was the changing of the FSUIPC button sequences as I activated the reverse thrust levers. As the level travelled through the first detent, each lever would indicate, in the FSUIPC software, the correct button number.  However, as the levers travelled through the second and third detent positions the button number would change and indicate button 4.  Button 4 is assigned to the speed brake lever.  Why was button 4 continually being activated? 

It was then realized that at the forward end of the spee brake handle, where the brake arm recesses into the throttle, there is a small button.  This button had been wired to button 4.  Button 4 is activated when you either raise the brake handle to arm/deploy the speed brake, or when a cam is activated by the reverse thrust levers (the levers travel over the cam as they pass detent two and three position). 

Once the issue was understood, it was a matter of changing the Button 4 assignment.

Speedbrake Calibration

This is far more difficult and challenging than I thought it would be.  I've spent many hours attempting to have the speedbrake operate in the correct manner, but have failed on all counts.  Without going into detail, sometimes it sort of works and at other times it fails.  The 0/0/4 phidget card has been installed and the two relays programmed (squat switch), however, for some reason problems continue. 

This is going to require some in-depth thinking and help from others.  It’s possible that a problem exists with the servo motor.

Continuing the above theme, I've just spent a few hours talking to a friend in the US discussing this issue. It seems that it's highly probable that the servo motor has been burnt out.

The intermittent behaviour and motor humming was most likely caused by the motor beginning to ove heat which eventually caused the motor to fail.  

In the meantime, everything else on the throttle quadrant appears to work correctly, which includes using the actual speedbrake lever to arm, partially open, or fully deploy the spoilers.  The only part that does not"yet work correctly is the automated movement of the speedbrake lever when the squat switch is activated on landing.

B737-300 Throttle Quadrant & Center Pedestal - Arrived at Last

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A big orange truck from TNT Express parked outside the house this afternoon and the driver began to offload a large wooden crate that weighed around 80 kilograms.  I could be only one thing – the Boeing throttle quadrant and avionics box (center pedistal) had finally arrived.   

Together, the driver and I manhandled the crate through the hallway of the house to the room in which construction of the simulator is taking place.  Removing a heavy piece of machinery from a wooden crate can be tricky, and the only method was to disassemble the box screw by screw – WOW what beauty!

Initial Thoughts

The throttle and avionics bay is a genuine aircraft part so there wasn’t much to not like; you can’t “immerse” yourself or get a more authentic experience than by using a real aircraft part.  The throttle originally was in use in a Boeing 737-300 with South West livery.  Unfortunately, the guy at the tear down yard didn’t document the tail number of the aircraft it was removed from.  It would have been nice to have a photo of the actual aircraft to place on the Blog.

The first aspect I noticed about the throttle was the build.  It’s a solid piece of engineering built to withstand the neglect of pilot use and now simulator use.  I don’t believe the throttle will ever be damaged from neglect my end – its’ solidly constructed.  The feel when you push the two power levers forward is - well – you just have to be here!  Manoeuvring the flap lever through the various indents is equally rewarding.  Knowing that the throttle was once used in a real aircraft by real pilots adds a completely new dimension to flight simulation.

Retrofitting and Connectivity

During the refurbishment of the throttle, I had decided to not bastardize the throttle to try and replicate the appearance a throttle from a Boeing NG.  Therefore, the throttle remains a 300 series throttle.  It has been repainted only where necessary and decals have been replaced only when they were unreadable.  The internal mechanism of the throttle has been completely striped, cleaned and serviced.  Parts, such as the huge cog wheels and unnecessary internal wiring have been discarded as these are not required for simulation use. 

To allow the throttle to connect correctly with flight simulator, three Phidget cards (0066 & 0064) & a Leo Bodnar card (BUO 836X) have been used.  The cards are connected directly to the front of the throttle casing and will not be visible once the throttle casing is connected to the centre stage of the main instrument panel (MIP). 

All the functions of the throttle operate with the exception of the stab trim switches, which can be linked to another FS function if required.  Trim wheels are functional with the use of a servo motor and the trim spins when electric trim is activated on the yoke.  Back lighting is integrated back lighting (IBL) using genuine Boeing 5 volt bulbs.

oem 737-300 throttle quadrant - initial thoughts: it’s built like a thunderbox

Current Status

At the moment I’ve only taken delivery and am in the process of connecting a Benchmark card to an external power source to allow power to reach the 5 volt lighting bulbs and servo motors.  I have little doubt that there will be teething issues with software as I configure everything for correct functionality, but I believe that this extra effort is worthwhile to be able to use a real throttle instead of a replica.

Center Pedestal

The avionics bay is a two-bay type.  Two-bay types were mainly used on the earlier Boeing classic series jets up to the 200 series, however, a number of 300 series aircraft used them as well as 400 series.  The bay was attached to the throttle when I bought it, so rather than dump it and replicate a NG three-bay; I’ve decided to use it to maintain authenticity.  I may at some stage in the future replace it with three-bay – I’ll see how things develop once I begin to populate the bay with avionics instruments.  One benefit of using a two-bay style is that once Weber seats are fitted to the flight deck there will be more room to squeeze past to get into the seat!

An interesting feature to the unit is the positioning of two oddly shaped aluminium pull downs.  At first, I had no idea what these were used for.  Then it dawned on me – they are retractable coffee cup holders.  What more can you ask for (laughing). 

oem 737-300 fire suppression panel

Fire Suppression Panel (FSP)

The fire suppression module was an afterthought.  A second hand unit was available and I decided to retrofit this with limited functionality to flight simulator.  At the moment IBL works, and when pulled, each fire handle does what it’s supposed to do.  At some stage in the future I may activate the fire bell.  But, at the moment it’s early days with regard to this.  Basically it’s a module that has to be installed into the avionics bay for aesthetics; a TQ without a fire suppression module looks a slightly naked.

More on the actual avionics bay at a later stage when I begin to populate the bay with instruments - much kmore interesting than looking at "naked bay"