Yaw Blues

After a couple Quadcopter builds, I built a Tricopter.  I thought there might be some efficiency gains, portability(folds down nice) and increased maneuverability.  

But this Yaw issue has me thinking quads again.

I used autotune and autotrim.  I still have a slow clockwise rotation going on.  I can trim it out with my transmitter, but then I can't re-arm the quad.  Also, the auto flight modes get mixed up with the trim.

I REALLY wish autotrim adjusted yaw... but from everything I've seen, it just does pitch and roll.

Is there any way to adjust yaw trim in the APM software?  Seems like such a necessity for tricopters.

Thanks for any help!

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  • Okay tricopter guys... still having the yaw issue.  I don't see anywhere to tune this.  Is is just dumb luck that everyone else is tuned?  Or do you take off the servo, twist the pivot mechanism and re-try?  Just kind of amazed that this isn't included in "autotrim"  it would be so nice.

    • adjust your Yaw P and D settings :)

      • Any idea which settings to start with?  Or what a .01 would do differently than a .04?  I think it's set at .02 now.  I will double check.

        thanks for the reply.

  • Having the same problem with a new Tri build myself, and not having a very easy time of finding info on the "correct" way to trim it.

    Is there even a manual for tricopters using APM anywhere?

    • I've found Autotune works very well for pitch and roll PIDs. Yaw is a bit trickier because some frame/motor combos seem prone to "yaw wobble" with APM. I've suffered from that and was able to cut out most of it by turning the Stabilize Yaw P value up pretty high.

      If you have a constant rotation going on, that's not a tuning issue, there's something else going on. Absolutely first, make sure that you've reversed the servo throw in Mission Planner IF IT NEEDS IT (I think that's RC7). Depending on your servo and how you built the mechanism, it may not. It's not enough to just reverse the RC Tx channel, it may also need to be done in MP.

      Second, make sure not all three props are turning the same direction. Third, look for misalignment of the servo mechanism. Finally, if none of that improves your problem try increasing your I value in the Yaw PIDs. The I factor is to deal with long term build up in errors.

      But if I had to guess, it would be that you need to do a reversal of RC7 in Mission Planner.

      Oh, and the APM Devs are currently working on adding Yaw into the Autotune setup.

      This thread is just a little dated, but it's a pretty good step by step guide to setting up an APM-powered tricopter and describes the RC7 reversal.

      • RC7_REV is set to "Reversed" (Trifecta frame) and I can control the yaw via TX inputs.

        I'm using the 1 CW and 2 CCW config - motor #1 is CW and the other two are CCW - the APM setup says either way is fine - do you have any reason to believe this setup is not as good as all CCW?

        See attached image:

        3702691180?profile=original

        > "misalignment of the servo mechanism"

        How would I check this?

        I'll check out the thread you posted, I hadn't seen that one and it looks like there's some good info in there.

        I've posted my build notes here that includes my default PIDs that I found from someone on RCGroups, maybe there's something useful in there?

        https://docs.google.com/document/d/19ukCQ95_6eGZYgwHyQqKBuvcJaGNBn2...

        Thanks!

        Quanum Trifecta tricopter build log
        Quanum Trifecta tricopter build log Started: 03/2015 Parts list Quanum Trifecta tricopter frame Afro 12A ESC + Multistar “Baby Beast” V2 combo pack…
        • SOLVED: I feel silly :) I started triple checking everything from the start, and realized that my rear motor was set up to spin CW, not CCW like I had thought.

          It's literally the worst thing to have to change on this Trifecta frame, requiring me to take apart the whole thing to get to the motor wires. I reversed the motor, had to replace the prop nut as well and it actually flies now :) It's a little jittery, but nothing that some tuning won't fix.

          Thanks for the help! I see now that perhaps the "All CCW" is perhaps slightly superior in that it removes any possible errors like this from happening in the first place ;)

          • Many times it's one, silly thing that gets overlooked. Not that it's ever happened to me.....

            I find the two CCW, one CW setup to be the best, although they both will work. By running all motors CCW the tail motor has to tilt a lot more to cancel out the overall torque on the airframe. But when running two of the motors opposite, those two torques cancel each other out.

            To help reduce my chances of error I always put a label on each arm identifying what the motor rotation direction should be, and I also mark my props. One less thing to have to think about when doing field repairs.

            • I have read that a tricopter frame is special in such a way that any motor direction combination will work. I have tried 1 CW - 2CCW and 2CW - 1CW setup. the latter is my setup (which is not discussed in the ardupilot website). Since any motor direction would work, it really wont be an issue. except for mono direction setup which somehow deals with the torque. 

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