Motorising a 737 throttle.

[fordgt40]

For some considerable time, I have been converting a Symulatory throttle to a better specification using dc motors and a clutch. I am now very happy with the result and will in due course post a complete account of the work on Ian Sissons site to add to my previous articles.

Basically, I removed all the internal mechanics and installed 12 volt dc motors controlled by an Opencockpits USBDCmotors card and a homemade clutch.

My specs/requirements were

Maximum 12 volt supply with a current draw of around 1 amp

Sufficient torque to pull the levers back from a full fwd position, if I recall circa 120 in/oz

High gearing to get the torque and contribute to achieving the correct lever speed which is around 5 secs from idle to firewalled.( courtesy of Ian!)

The motors I used are 940D models with a reduction drive of 721 to 1 and the link is here

http://www.mfacomodrills.com/gearboxes/940d_series.html

There is a full data spec and pricelist on the site

Additionally, I used a belt drive and ribbed pulleys between the motor and throttle lever arm with a ration of circa 4:1. This gave me a range of speed movement that could be changed by either reducing the motor voltage or through the PWM of the controller card.. The motor works quite happily at 5 volt and still with adequate torque

Also, I needed a clutch as the motor gearing prevents manual operation of the levers and I attach pictures of the completed unit and components I made.

For your information, an explanation of the components from top left is:-

Polymer end bearing

Turned main drive shaft with grub screw to secure the motor, note also the "key" on the shaft to stop the pressure plate from turning. Threaded section to allow variable "force" on pressure plate

Polymer end bearing

Rubber friction plate

Spur gear for driving the potentiometer shaft

Ribbed pulley to drive the belt to throttle lever, with polymer bearing between pulley and main shaft

Rubber friction plate

Keyed Pressure plate

Spring to provide variable "force" on pressure plate

Threaded force adjuster

Ribbed pulleys and belts were sourced from

http://www.motionco.co.uk/timing-belts-timing-belts-c-25_38_27.html

I also attach photos of the completed unit and fyi I used three turn wire pots with gearing to ensure that I got full pot movement across the circa 80deg of throttle arc movement – this avoids "jittering" and allows for smooth slow movement. You will see on the "mounted motors" photo that the spur gear on the pot shaft has changed to a plastic one. I actually made the spur gears on my milling machine using a home made hob which was fine for the 80 tooth spur gear. However, my home made 12 tooth spur gear was pushing things to far and it would not engage properly!

I have had a few teething problems with the clutch ie the belt drive is a side load on the shaft/pulley joint and is "stressing" the plymer bearing. I may have to retrofit a needle roller bearing. The actual clutch "break" works very well and smoothly

The future article on Ian`s site will include how I made working trim indicators, spoiler arm with flight detent, backlighting, and automatic parking break release

Hope this is helpful – if you need any further info, just ask

David

[jackpilot]

whaooo!

[jetpilot]

David,
Thank you for the info. Right post at the right time.
I was wondering if you can post a little video of the system working.
Thank you
Roberto C

[Maurice]

This is some SERIOUS project   OUTSTANDING work !!!

Can you explain how the manual override would work with FSX (or FS9). As far as I know, if the autothrottle is on, moving the throttle levers has no effect. So, did you incorporate some sort of feedback circuit that shuts off the autothrottle if you do a manual override?

Anyway, your skill level is just plain amazing.

Maurice

[fordgt40]

All - Thanks for your kind comments and symbols

Jetpilot

If I can work out how to post a video, then I will. However, I can assure you that the lever movement is silky smooth with no jittering whatsoever.

Maurice

The clutch is basically there because you cannot manually drive the levers against the motor gearing - so the clutch enables manual operation. I am, however, programming the feature that if the levers, whilst under A/T control, are moved such that there is more than 10 deg of difference between them - then the A/T disconnects and does not reconnect until the difference is less than 10 deg.

This is, I believe, a feature on the real plane and is easily simulated  in SIOC which controls the lever logic and through the offsets in Sim-Avionics.

Moving the throttle levers whilst under A/T control has no effect on my throttle, the levers return to the commanded position with no change in thrust

Currently, sipping much beer just watching the levers move 

David

[fordgt40]

Maurice

Apologies, my original post was misleading about "manual intervention", hence your question. I have now edited and corrected the OP.

Regards

David

[Maurice]

I am, however, programming the feature that if the levers, whilst under A/T control, are moved such that there is more than 10 deg of difference between them - then the A/T disconnects and does not reconnect until the difference is less than 10 deg.

David

Very cool feature!

Maurice

[XOrionFE]

Awesome work David,

I am working on my real TQ using the method Rob posted in another thread and will be using OC motors card to drive the motors with SIOC as well .    Your work is pioneering and I look forward to seeing more.   I hope you will share your code also once done.   Again...very nice work!

Scott

[fordgt40]

Hi Scott

The sioc programme is no problem
Just one word of caution re the OC DC card - it only takes 1 amp per motor and does run very hot! I had to put some heat sinks on the ic`s. You also need to solder some of the ic pins together to spread the load, unless you buy it already made and tested. If you need specific details then let me know

Regards

David

[XOrionFE]

Good to know.   My board is the premade one.  If you have some details that would be great.   I have to check my motors to see what kind of draw they have.   Looking forward to meeting again next week at the get together if you are coming.   Going to be fun discussing all this stuff in person!

Scott

[jackpilot]

Yep David is on the VIP list!

[fordgt40]

Scott

Happy to repay the help you gave me when  I visited and flew into the houses at the end of Midway runway  Will try to find the info re the OC cards for you

Jack

Surely not a VIP, just an old hack  though will be great to meet you in person

Regards

David

[MLeavy737]

All - Thanks for your kind comments and symbols

Jetpilot

If I can work out how to post a video, then I will. However, I can assure you that the lever movement is silky smooth with no jittering whatsoever.

Maurice

The clutch is basically there because you cannot manually drive the levers against the motor gearing - so the clutch enables manual operation. I am, however, programming the feature that if the levers, whilst under A/T control, are moved such that there is more than 10 deg of difference between them - then the A/T disconnects and does not reconnect until the difference is less than 10 deg.

This is, I believe, a feature on the real plane and is easily simulated  in SIOC which controls the lever logic and through the offsets in Sim-Avionics.

Moving the throttle levers whilst under A/T control has no effect on my throttle, the levers return to the commanded position with no change in thrust

Currently, sipping much beer just watching the levers move 

David

That is really awesome work! Amazing... Just wanted to share some info for you on how the autothrottles work in the real airplane. Not sure if i read what you were doing correctly however maybe i can save you some time.
  On the real bird when the autothrottles are engaged, assuming there in a commanded hold mode and not just in the Armed mode, you can overide them at anytime. When you do this nothing disengages and the power will respond to your input.  Just be aware that the autothrottle motors will continually try to drive the power levers back, or forward to where the FMC is telling them to be.  They degree difference does matter.  If you override them, you will need to hold it there and you can actually feel the slight force of the motors trying to drive them.  Does not take that much force to override them but its there.
   I believe one of the challenges when using FS to drive the autothrottles is actually determining where FS thinks they need to be and getting your own software to attempt to drive them back or forward to that position when overriding them. I messed with FS driven autothrottles before and thats exactly what it was.. A mess! Lol. Full power, idle, full power, idle ..all it was trying to do was hold an airspeed lol..
  Hope that helps a little.. Let me know if you have any questions..

Mike L

[fordgt40]

Mike

Great information and many thanks. I have some more programming now  . The problem is now determining when the throttles are being manually changed against  the MCP commanded thrust. This could be fun!

Thanks again for your input

Regards

David

[Volante]

Amazing project, David!

This is another way of getting rid of the heat from the OC DC motor controller card.
A small 12Volt PC fan does the trick.

Vidar

[fordgt40]

Vidar

Great idea, many thanks for that.

Regards

David

[MLeavy737]

Mike

Great information and many thanks. I have some more programming now  . The problem is now determining when the throttles are being manually changed against  the MCP commanded thrust. This could be fun!

Thanks again for your input

Regards

David

No problem David!  Btw, your not the only one that has more programming to do. Boeing does as well. 

Few days ago we got a pilot bulliten about disconnecting autothrottles when in mountain wave turb or moderate to severe turbulance.  Flying last night KORD to KSEA  working around some wx in light turb, started getting a little stronger.. Next thing you know the power starts coming back to idle as we hit an updraft.. We both look at the throttles and realize whats going on.. He disconnects then A/T, goes to max continuous and it literally takes 15-20 sec for the power to get back up there.. Meanwhile were out of the updraft and into the downdraft and the airplane is approaching the yellow stick shaker arc on airspeed..  Had we not disconnected the authrottles, no doubt the airplane would have stalled itself!  The bulliten warned of this happening and the slow engine respool time due to a software update.. Nice huu?? Lol..

Mike L

[Flying_Fox]

Great work David!

I am installing my 737 TQ into the base now, next step is interfacing, so I am going to pick your brain on the way from the airport to FDS. 

Nick

[fordgt40]

Nick

No probs - happy to help

David

[fordgt40]

Mike

I have heard about rotor clouds but did not realise they could have that much effect

Programming the "realism" into the throttle programming is proving one step too far, as you thought. The SA software author does not think it practical and the best I can do in SIOC is to try recognise manual intervention, save the thrust mode, disconnect the A/T, respond to the manual thrust and then reverse the process. However, how will I know when manual intervention has ceased

On balance, I think that I will just ignore any manual intervention and rely on the A/T disconnect button - Maurice you were right

Regards

David

[MLeavy737]

Mike

Programming the "realism" into the throttle programming is proving one step too far, as you thought. The SA software author does not think it practical and the best I can do in SIOC is to try recognise manual intervention, save the thrust mode, disconnect the A/T, respond to the manual thrust and then reverse the process. However, how will I know when manual intervention has

Regards

David

Im just getting around to programming my throttles and i have a close setup to yours i believe. DC motors with a belt driven slip clutch system. Ill let you know how i progress.  Im using phidget cards and c++.  Well see how much custom code is required to get these things working.  Well see!

Mike L

[fordgt40]

Mike

I think that apart from myself, there are at least two others here who would be very interested in what you are trying

Keep us posted

Regards

David

[XOrionFE]

Yep, definitely Mike.  Me too....

Scott

[Flyboyandre]

Looks amazing Scott! Are you making one for me before you clean up your workbench?

[MLeavy737]

Mike

I think that apart from myself, there are at least two others here who would be very interested in what you are trying

Keep us posted

Regards

David

Will do guys... The way i think you need to approach this is to Not use any of the built in autothrottle functionality in  Flight Sim at all.  in other words just drive the throttles in your own code as if you were moving them yourself.  Thats the overview.  Only problem is this could require a complete autopilot rewrite because then autothrottles are closely tied into the autopilot system.  Not sure yet but thats the way im approaching it.

Mike L