Tricopter yaw single oscillation after input

Hi All, I’m relatively new here (but have been lurking for ages).

1st, thanks to all the devs and contributors for making ardupilot so awesome!!

2nd, I’ve got a question about tricopter yaw tuning.
I have been flying a homebrew tricopter for about 6months with 3.0.1, and had it flying well except that when yawing - it would overcorrect a single time after a movement. I just updated to 3.1 and am having a similar issue. The tri is rock solid, and needs a bit of stick input to initiate yaw, and then it will yaw appropriately (maybe a little on the fast side) and when I release the stick it will do a single oscillation in the opposite direction, then it will stay rock-solid again on the new heading.

The yaw mechanism is the simple-copter tail block design and there is very little slack in the mechanism, and I think it is a PID issue. Is there any documentation on using/tuning the yaw on tricopters? I can’t seem to resolve this by just randomly adjusting settings.

Is there a procedure to tune the yaw to get a steady response, or is there some documentation of each PID value with respect to yaw?

Cheers for any help.

I’ll take a stab at an answer as I’ve just gone through a long process of getting a tricopter dialed in. Without knowing what your current P, I and D values are, I’ll speak in generalities.

The fact you have an overshoot suggests your yaw P is either too high or you have a low yaw D. The P value is sort of how fast the tricopter corrects to your desired new position and the D value moderates the overshoot. If P is low, you don’t get much overshoot but the response is slow. If P is high, response is very quick but you’ll get lots of overshoot. Adding in a little D allows you to use a higher P, for quick response, but reduces the overshoot.

From your description it sounds like your yaw P is either OK or on the high side. I’d play with the D value. If it’s set to zero, not uncommon for tris, you could add in a very small amount and see what happens. I’m running a D of .003 with a P of .230, but my tri may be nothing like yours.

You can also put your yaw D on Channel 6 tuning, adjust the value while it’s flying and try different values. Be careful about not jumping to too high a D value because it can cause rapid oscillations and control becomes difficult. D should be pretty small. A cautious approach for D tuning, if it’s currently at zero, would be to set your channel 6 knob to vary D from .001 to .005.

Here’s a link that has a decent PID discussion.

Thanks OtherHand, that is exactly the info I was hoping for!

You’re correct - my D value is 0, and I was unsure whether it was even used in tricopters, so I hadn’t played with it yet.

I’ll have a play next opportunity I get and let you know how I go. Thanks!

OtherHand, that was spot-on. Cheers for the help.

Here’s the vid from the test this morning. I know there’s a bit of rolling shutter due to vibrations, but I’ve got that solved after balancing the props. Enjoy.