How to reverse yaw control on Tri-copter

I have serious problem how to configure my tricopter (2.0.39). Roll and pitch are correct. Yaw(rudder aka tail servo) was incorect thus i reversed RC channel via MAVlnk (btw i don't understand why dip switches are not enabled anymore in ACM...)

Now the servo moves correct according to radio stick movement but when i do yaw movement of frame by hand servo moves incorrectly - by this 'correction' frame would start spin infinitely.

How can i reverse this?

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  • This took me a couple days to figure out and google search much like yourself.  So I would just like to post the google search terms I was using to describe the problem.  This is a great community, thank you everyone that posted!

    Ycopter yaw is erratic

    Tcopter yaw is erratic

    tricopter spins uncontrollably

  • Yes, I'd like to confirm my success with reversing of the servo. I had a perfectly fine working tricopter with a Corona DS-238HV servo.  I then switched to a Hitec H-82MG. (Old servo was getting sloppy).  No changes had been made to the software or mechanical arrangement.  However, I found that both radio Yaw control and APM Yaw correction were now backwards.  (Rather, the new servo responds reversed to the same PWM as the old one).

    I was able to fix this by changing RC7_REV from 1 (Normal) to -1 (Reverse).  This effectively reversed ALL PWM signals to the servo.  No changes were made to RC4_REV or in the radio.

    • Hey Harry, glad to hear you're going the tricopter route, its certainly a fun one. I'd say for you.. the most vital piece of advice I've discovered is that the tricopters tail, Yaw stick that pivots the copter around on its horizontal axis, NEEDS to be reverse of the input you give it from the transmitter. so I ought to look like this in mission planner, etc.

      With RC-7REV @ 1 --- 

      Transmitter >>> Left Yaw

      APM Planner radio calibration page >>> Left Yaw

      Tricopter Tail Movement >>> Tail tips to the right (This is due to the fact that the copter tail wants to tip it this direction, which pulls air to the right, causing a left turn - yaw)

      and vise-versa for Right Yaw.

      Obviously when you're spinning up your motors, its a bit scary seeing the controls be reversed esp not knowing thats the correct way, so its incredibly nerve racking to just say oh well and get on with it, but this step is important to get over the hump. Once you get it airborne, everything sorts itself out. What I do specifically in this case is when I spin up the motors to get going, if my tail is leaning to either side, I'll give small amounts of yaw stick, flicking back and forth, to get it to center (which it eventually does) and at that pt, I lift off. 

      If your problems persist, let me know and I can send you my params for my tricopter that functions normally and or some more help.

  • Checking through the full parameter list I noticed on FRAME that my parameter was 1 for X configuration but the attached notes state that tricopters and helis should be zero.  So I changed the param to zero and checked again for yaw....still no correction. 

    I also checked the compass offests and my x axis offset is probably too high at 253.  I will re calibrate and report back.

    • I don't know if you're having the same problem as me. But here is my problem and solution. I built a tri. The servo direction was proper as controlled by my transmitter. But arducopter's yaw correction was backward which would cause immediate rotation of increasing speed. My fix was to change RC7_REV from 1 (Normal) to -1 (Reverse). This fixed the arducopter's yaw correction but made the servo movement backward as I control it. I fixed that portion by reversing the rudder direction in my controller.

      It took me a while to figure out there are two yaw control mechanisms at work. Controller input and ardupilot input. Both have to be working in the proper directions.

      • I can confirm your solution is how I did my tricopter. 

      • I am currently trying to tackle this problem. I believe my servo is reversed, when I throttle up it tips to the side a bit and yaws the copter round and around. I'll try all of your suggestions including the rudder reverse. hope something can help me. 

  • For those still looking or using MP 1.2.88 plus.

    RC Reverse (RC7_REV)

    Almost at the bottom of the advanced parameters list.

    Thanks Palo.

    • Reversed this in the advanced parameters section, then saved it but it hasnt made any yaw is still reversed ;(

      • Thought I fixed everything by reversing the yaw in my TGY 9x transmitter but this has made things worse.  Yaw is actually moving in the correct direction but servo starts up all the way over to the right.  

        When I armed the tricopter started spinning around in circles on the floor, my first reaction was to switch of the transmitter off, but this made the tricopter spin even faster out of control towards my direction. Luckily it hit the table leg before it got to me and I threw a blanket over it then pulled the XT60 plug. 

         I did have the tricopter flying in stabilise mode previous to all this but it was very confusing to fly with the yaw controls reversed.  Im starting to get wary of APM 2.6, Im not happy with the way you cant quickly cut the power.

        There must be something Im doing wrong because reversing RC_7REV seems to work for everyone else except for me.

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