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Motor RPM for trim indicators/wheel and Speed brake

Started by kurt-olsson, January 16, 2020, 05:15:00 am

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Hi all!

i have soon finished my final setup of the mechanics for the trim indicators/trim wheels and also the speedbrake.

Right now i am testing the setup with two 6RPM motors. This is to slow for trim indicators that are hooked up to the original jackscrew. I also think this is to slow for the Speedbrake even it has an extended arm it rotates with.

I would also like to know what RPM you have for the trim wheels. I can always slow them down with PWM so i need some sort of Max value for the RPM in any cases.



January 16, 2020, 10:57:09 am #1 Last Edit: January 16, 2020, 11:00:28 am by FredK
Hi Kurt...

Regarding the trim indicators and speed brake....I don't quite understand how you have your motorization setup since it appears that you are using stepper motors (or simple DC motors??) for those.  I am using servos/pots  for those combined with retooled linkage mechanisms.   I believe the latter is pretty much the standard approach of how to do it.

Regarding the trim wheels.....I have seen references indicating a max rotational speed of about 5 turns per second for the trim wheels.  That is second-hand info but is probably about correct based on eyeballing videos of the wheels spinning in real cockpits, and of course that is very fast.  I do not recall seeing any home cockpits that quite match that speed....most (including mine) are slower given the mechanical challenges involved.  My wheels do about 1 turn per second or a little less which is definitely on the slow side.  Your speed of course will be dictated by both the ratio of your gearing and the rated RPM of the motor. So you can do some calculations to determine a ballpark RPM of where you want to be taking into consideration the robustness of your mechanical arrangement.  Part of that issue however involves balancing the RPM and torque specs for the motor. Unlike the throttle levers you will need a fairly high torque rating for the trim wheels.

Fred K
Boeing 737NG-800, Prepar3D v4.5, Sim-Avionics 1.964, SimSync multi-channel (curved screen), Optoma 1080GTDarbee projectors (3), Fly Elise warping, FSGRW weather, FDS OH panels and CDUs, SimParts MIP, FDS SysBoards (OH), CPFlight MCPPro and pedestal panels, FI Gauges, PFC controls, converted motorized TQ (SIOC), Weber seats


My 737-800 full-scale cockpit is complete and been put in storage (for sale). Now onto my full-size helicopter project. An AOPA member and LifeTime member of National Association of Flight Instructors. Please note that I am a self-employed professional cockpit builder that provides consulting to defense contractors and civilian schools and airlines.


Thanks Fred and Jim and sorry for not providing more info.
I am lucky to have the real jackscrew for my trim indicators, i think i have this figured out.

For the trim wheels i will be aiming for something like yourd Fred.

Jim, thanks for the video, will make an aproximation as seen in the video.

So, now i am covered i think. Thanks

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