Auto Throttle

Question

Hi Vlad

For 2 weeks now I have been trying to solve a problem getting the auto throttles to work correctly

Im using Nema17 steppers and TMC2208 silent drivers to drive Zibo 737 throttles - They have "Dir" and "Step". I am also using 10K Pots to control the throttles in manual (with the recommended CAP at the terminals of each Potentiaometer as per RSC (1000 Micro Farad)

If I run the steppers without the Pots connected they work perfectly and the throttles move as expected. If I run the POTS (throttles manually) without the Steppers connected they work perfectly. I can calibrate them all and there is no noise or problems

As soon as I connect them both in the system, The throttles vibrate and jiggle. If I engage the auto throttle the steppers work perfectly again and the throttles work smoothly and as expected. As soon as I disconnect the auto throttle both throttles start vibrating and moving erratically. Because they are connected to the Sim datarefs the sim throttles also move erratically. Ive tried calibrating numerous times

Ive rewired the system 2 times from scratch this week. I have purchased new power supplies. Everything is grounded correctly, but still the same. I've tried 5 power supplies this week. Ive tried driving the steppers on 12v and 24v and a separate 5v stable power supply for the logic

Ive tried full and quarter step and all options for stepper control in the RSC software

I dont know what else to try. Do you have any ideas?

Many Thanks

Mark

Answer 1

Hi Mark,

Please open the A/T section in the configuration tool and read the notes related to the A/T settings. You need to use additional signal for the servo/stepper power.

It seems I had this described somewhere on the website page (or maybe in this forum),  but probably not.

Vlad

Comments

Hi Vlad,

I encountered the same problem as Mark, and I thought that my problem was the fact that  with the B737 auto pilot, there are 3 instances where your A/T should engage, ie N1, SPEED and LEVEL CHANGE. I am in the proccess of using an Arduino Nano to simulate a nor gate, and using the MCP's LED outputs (for the three mentioned buttons) to enable or disable the stepper driver.

So all three LED's will have an input to the Nano, and if any one of the inputs goes high, the Nano will output  a digital high to the stepper driver Enable pin, thus enabling the stepper motor

This should have the  same effect as what you described. So the throttle should move freely, even while the A/T is armed, but as soon as any one of the buttons are pressed and the LED comes on, the stepper driver will enable and the stepper motor should control the throttle. I realise there must be a more effiecient way of doing this, but that's how far my electronics knowledge goes... ! What I do not understand is, what will the reference for the  stepper motor be,  if the pots on the throttle stems are blocked by the plugin when A/T is engaged ? I hope this all make sense ?

---

Hi Vlad

thanks for your reply

I’ve done the mod now and assigned a dig out to disable the Pots.

It works ok, but what I have noticed is, if you turn off A/T, then move the Throttles by hand and leave them slightly out of sync, say Thr1 on 50% and Thr2 on 54%, when you then engage A/T again the throttles remain out of sync

The problem is when the throttles then go to idle, the one throttle hits the stop and then tries to drive past it, because the other throttle has not reached idle yet

I think I’m describing Francois question above. With the Pots disabled you loose the closed loop control

is there a way to resolve this? It’s nearly working perfectly but not quite

---

Mark, 

I eventually got the A/T to work correctly by following the instructions ! I feel really bad for not reading the instructions like I should have done from the start !

I also found that by setting the N1 rpm to something like 96% prevents the throttles to run hard against the stops and the idle setting also never runs against the stop. Otherwise the A/T works perfectly ! All in all...a very easy setup, as long as you follow the instructions...!