Reversing the PID output (direction)


I am using an APM 2.6 in a trex helicopter, I have set it up according to the steps given in the APM page (Trad Heli Configuration through the Mission Planner). The displacement of the servos in the swashplate, tail, and throttle correspond exactly to the stick in the radio control. Now, I am tuning the PID gains and I realized the output of PID is reversed, i.e. if the helicopter moves counterclockwise (from top view) then the PID output reacts in the same direction of the movement therefore the helicopter moves faster counterclocwise.

Does anyone know what is the best way to reverse the PID response?. What I did to solve the problem with the tail was reversing the direction of it in mission planner and reverse the direction of my radio control (Channel 4) but I am not quite sure that is the best solution.

I attach the picture of the initial configuration before reversing Channel 4.

Thanks for the help.

This is likely a radio setup problem. The pitch, roll and yaw outputs from your radio should not normally be reversed. Likewise, the radio inputs into Arducopter should not be reversed. In fact, they have removed these reversing buttons from the main radio calibration screen and they are only accessible in the Full Parameters List. Make sure they are not reversed.

If it’s none of those things, then come back and post your full parameters, and I’ll have a look.

Hello Rob,

Thank you for your reply. The problem is solved. The mistake was that I placed the APM board in the helicopter in reversed direction without changing the parameter in the MP, that is why I never had the correct PID output. So I just placed the APM board back to forward direction and I obtained the correct PID output. The final setup is attached.

Just a quick note about the setup. I think according to the official page at least one of the output from my radio has to be reversed, it says in section “Configuring the servos” in “Trad Heli Configuration through the Mission Planner” : You may need to reverse the collective pitch setting on your radio. Likewise, some of the inputs into the Arducopter have to be reversed, in the same section it says: Don’t be surprised or concerned if one or two of the servos move in the wrong direction just click the rev check box.

Hence, in order to obtain the correct displacement in the swashplate, I had to reverse ( by clicking the check box ) 2 servos in MP and for the pitch I had to reverse the output of my radio control (Channel 2). Now the same correct displacement happens when I reverse only 1 servo in Mission Planner (Servo 1 position +60) and 2 outputs in my radio (CH 1 and CH6), but I noticed after some tests that even the displacement is correct the output of the PID will be incorrect. That is why there is only 1 possible configuration of the servos in MP and radio.

I attach the final setup of MP and my radio, to obtain the correct displacement in swashplate, tail and collective pitch, as well as PID conpensation.

Can you furnish me a channel map from your receiver to the APM 2.6 and also where you plug the ESC on the APM 2.6 port (probably channel 8).



Thank for you help. I finally figured out what was wrong with the set up as shown in WIKI.

After changing to an 8 channel Futaba receiver (not WIKI’s issue) I connected the following:

Receiver 1 -> APM 1
Receiver 2 -> APM 2
Receiver 3 -> APM 3
Receiver 4 -> APM 4
Receiver 5 -> APM 5
Receiver 6 -> APM 6
Receiver 7 -> APM 7
Receiver 8 -> APM 8

I plugged the ESC into the APM output channel 8. I am using the power module and JP1 is removed from the APM 2.6.

My final problem to solve was the darn thing wouldn’t arm.

So, in desperation, I mixed the channel 3 (throttle) on my Futaba 10 channel T10CAP transmitter as the master to channel 8 as the slave (the calibrate radio page shows channel 8 working in concert with the throttle channel). Now it works perfectly and will not arm unless in stabilize mode and probably the other modes outlined in WIKI you can arm on (I only tested in the stabilize mode). I also made the transmitter aux selection for channel 8 to NULL. I am using transmitter channel 5 (Aux 1) as my 3 - position flight mode switch and I have set up transmitter channel 6 to dial VrC and channel 7 to dial VrB. I’ll end up using transmitter channels 6 and 7 for accessories or tuning.

The only channel I had to reverse on the transmitter was the throttle channel 8. I did reverse channels 2 and 3 on the Heli Setup page and now everything works great. I hate to admit it but until I order my training gear I am not going to attempt to fly even though I have a lot of time on helis. Again, thanks for everyone’s help!! This is lengthy with the hopes it will help someone get his heli setup.

I don’t understand why you had to mix Ch3 into Ch8. That should not be required. I think you have some mix-up regards the H_RSC_Mode. Do you have it set to 0?

If it is not zero, it won’t allow you to arm unless Ch8 is all the way down. That might have been what was preventing you from arming.