Does it matter what servos are used for cyclic?

My TRex 500 has flown for many years with a BeastX FC, and recently I converted it to a Matek H743MINI FC with Arducopter 4.3. It’s flown bare-frame a couple of successful test and tuning flights with Arducopter, flying in Stabilised, Loiter, Pos Hold, and RTL modes, so yesterday I installed it back in its scale Hughes 500 fuselage without making any changes to its or the Tx’s programming. When I hooked it up to MP to recalibrate the compass, firstly I got a Prearm error message something about the motor (sorry, can’t remember exactly), but when I twiddled the Tx sticks I realised that the left and right swash servos seemed to have become reversed, and the rear one was stalling intermittently at the top of its travel (swash not physically hitting its limit) and was becoming hot.

When I was using BeastX, as part of the programming I had to specify the servos frequency and pulse length, so I’m wondering if this is critical with Arducopter and can it be programmed. In this heli I’m using Hitec HS5245MG which with BeastX would use a frequency of 200Hz and a pulse width of 1520us when used for the swash. Does it really matter, and is it possible that Arducopter and/or my FC has caused the servo failure?

I have another TRex 500 and a TRex 550 using Arducopter FCs with Align servos, which according to BeastX should use the same parameters as the Hitec ones. I don’t want them to fail in the air.

Hi Allen,

could it be that you accidentally did not perform the compass calibration, but realigned the FC orientation. If so, now the Fc assumes an incorrect mounting orientation. That would explain that the servos are running totally wrong.
This is just a guess on my part.



Could you please post a log or the param list of it as configured when you put the Hughes 500 fuselage on?
That would help me see how your servos are set up. If you just put the fuselage on and did nothing to the controller or Tx than none of what you are saying makes sense. Like you said. You may have had to calibrate the compass but that should be about it.

Checking again today I realise that only one servo is reversed – the front left one – but there’s something wrong with the rear one for it overheats and regularly sticks at the top of its travel. I’ll post the param list tomorrow when I get back into the workshop. Three new servos arrived yesterday, so they’ll be installed during the week and the whole setup re-done from scratch.

heri, I doubt if I realigned the FC orientation, mainly because the compass calibration menu is easy to get to, and I did go through all the twists and turns routine and got a satisfactory completion. I can’t even remember offhand where the FC orientation is specified :grin:

Thank you for posting.

I’ve done a lot more stupid things by accident during my years of model flying.

I know what you mean heri :laughing: Anyway here’s the param file as requested by Bill. The reason for the fence is simply to prevent me taking off without a valid GPS position.
Hughes 500 FENCE_TYPE set to altitude only.param (20.8 KB)

P.S. I’ve just compared this file with the parameters I had before, and see that SERVO1 is normal now and was reversed previously. Dohhhh! Correcting that makes the swash work correctly.

But that doesn’t explain why SERVO3 was heating up and stalling, so a knowledgeable review of the param file might reveal something. Anyway, because of the bad SERVO3 I’m now replacing all three of them. Also, even thought there’s no PreArm: messages, the heli doesn’t go through its normal servo-cycling routine when powered up. I may have disabled that by accident, but I can’t remember which parameter it is :thinking: