I just build a Tri based on ArduCopter. I had some issues with yaw and did some changes in the code. In this post I want to share my experience and I would like the developers to take my changes into the official release, that it will be easier for others to build a Tricopter.

First of all, this is the result:


One of the most interesting mechanical parts, the Yaw-Servo:

Now my yaw-issues and solutions, starting from code release 2.1:

1) Yaw-Servo not in middle position on "power on"

2) Yaw-Servo reverse with Mavlink RC7_REV

1) Yaw-Servo not in middle position on "power on"

Issue: On "power on" the Yaw-Servo moved into mechanical limit (bad sound, high current consumtion and reduced lifetime for the servo). After a few seconds it returned to the middle position.


In file "radio.pde" in function "output_min()":


    APM_RC.OutputCh(CH_7,   g.rc_3.radio_min);

By this:
    APM_RC.OutputCh(CH_7,   g.rc_4.radio_trim); // Yaw servo middle position
    APM_RC.OutputCh(CH_7,   g.rc_3.radio_min);

2) Yaw-Servo reverse with Mavlink RC7_REV

Issue: Depending on how you mount your Yaw-Servo the stabilisation of yaw can run in the wron direction. Reversing yaw on the remote doesnt help. You need to reverse the servo or change it mechanically. To reverse the servo:


In file "ArduCopter.pde" in function "fifty_hz_loop()":

    APM_RC.OutputCh(CH_7, g.rc_4.radio_out);

    APM_RC.OutputCh(CH_7, (   (-1 * (g.rc_4.radio_out - g.rc_4.radio_trim) ) + g.rc_4.radio_trim  ) );

I got this change from this Link!  Now you can reverse the yaw-servo by putting "-1" to the parameter "RC7_REV" via Mavlink.

Regards, Igor

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  • Have the same yaw issue with my in-the-loop tri. thanks for writting the info.

    BTW: what the weight/configuration of your tri? 

  • I had been meaning to start a thread since a while. ArduCopter has Serious issues with Yaw on Tricopter. Yaw is very sluggish, when a Tri is usually very agile. I had used 2.0.47 i believe and then gave up. 

  • Thank you very much...

    the fix for the servo movement is exactly what i need for my tricopter. Not because it is moving beyond its mechanical limit, rather because the sudden movement of the servo+motor puts my frame into oscilation which prevent the gyros from initializing properly.


  • That is a nice looking Tricopter, here is a question, I wonder what kind of RC equipment are you using please as at antenna is very long?

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