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.