Information on real A/T interfacing

[Mark]

I posted a picture of my A/T motor design in another thread:



I've had a few people message me for details so here is my response.

What motor did you use, and where did you buy it from?

We had a bit of time pressure so I simply wanted to buy the biggest motor I could fit in the available space that was easily drive-able from a H-Bridge board without breaking the budget. I didn't want a gearbox as this would add extra noise that you wouldn't hear on the real AC.
(So no AC/DC brushless motors) [This is the 'anti-faff' principle...]

The 'biggest motor' simply because the motor will be operating at such a low speed most of the time, near the really inefficient stall torque region, so a large motor ensures sufficient torque and also a large thermal mass for the electrical power wasted to ensure cool operating temperatures over 7 days of continuous operation. As it turns out - I made a good choice, and the motor barely gets warm.

Motor:
DOGA DO16241023B00/3009 24V DC Motor 2000RPM 0.2NM
Source:
https://goo.gl/XMT5CJ (Vendor: Conrad Electronic)

What did you use for the universal joint?

There is the awkward angle transition you can see in the picture due to the floor getting in the way. On the real AC there is no floor, just a large (relatively) void area. There is a downside to using a universal joint (or at least the non-lubricated one we have) - it adds restrictive torque and varying torque at that (as it rotates, it alternates between being easier and harder to turn). Thankfully it's not too much and I was able to tune the H-Bridge and control algorithm to make it unnoticeable.

Part:
Huco Universal Joint 103.16.3232
Source:
https://goo.gl/wTTojs (Vendor: RSWW)
Note: I used a 10mm to 8mm shim on the motor shaft.

What did you use for the hex shaft?

This is the part that requires the most 'tuning' - I used either a 10mm or 3/8" hex tool, cut down, and turned on the lathe to give it a shaft that fits in the universal joint. The remaining hex shaped end should be tweaked until it fits in the gearbox input spline. Requires a bit of persistence and tweaking before it fits.

What did you use for the H-Bridge?

In keeping with anti-faff, I just picked the biggest H-Bridge I could find at a reasonable price. This ensures minimal heating. I paired the H-Bridge up to a Teensy with Ethernet (this is a standard arrangement we use all over the sim so we don't use any failure-prone USB connections).

Part:
Pololu High-Power Motor Driver 24v20
Source:
https://goo.gl/Cllxx0 (Vendor: Pololu)

Comment:
If I had time, I would add an encoder onto the motor so I could measure the velocity and drive the A/T with a constant velocity (where the motor torque would just vary to maintain the speed) rather than the open loop constant torque solution currently (where, if not tweaked correctly, putting your hand on the throttle could cause the motor to slow down). A huge benefit of this is the varying torque of the universal joint simply wouldn't matter. A easy future improvement maybe.

I hope that helps a few people, post any questions you have here.

-Mark

[garys]

Awesome info Mark, Thanks for sharing.

Gary

[B747-400]

Hi Gents,

I purchased the 12 V version of the mentioned Motor. If you would like to see my approach of installing it into my genuine 747-400 TQ be welcome on my updated homepage!

Cheers
Hans

[Mark]

I purchased the 12 V version of the mentioned Motor. If you would like to see my approach of installing it into my genuine 747-400 TQ be welcome on my updated homepage!

Looks great, I wish we didn't have a floor in the way - your arrangement is exactly how I'd like it to be.

[B747-400]

Sometimes the buildings around our sims are a pain ... I will run into troubles with my visual ... lack of space 

Cheers