Disclaimer: I'm not sure where the best place to get help, so I've also entered the same question at: http://www.rcgroups.com/forums/showthread.php?t=1776457 and http://diydrones.com/forum/topics/apm-2-5-firmware-version-2-8-1-yaw-trim, sorry for the duplicates.
Hello, I recently upgraded the firmware of my APM 2.5 to 2.8.1 and on the very first flight post-upgrade I noticed that the heading of the copter rotates counter-clockwise. I have to compensate with the yaw stick in a very significant manner to stop it from spinning. The other axes (roll, pitch) have no issue.
I order to fly comfortably during the last flight, I trimmed the yaw on the transmitter to stabilize the yaw and was actually able to fly well like that, but from what I've been reading, it is not recommended to trim the transmitter on multi-rotor aircrafts, and much less on the yaw axis.
I'm not sure if it this is an issue with this release of ArduCopter (2.8.1) or hardware issue with my aircraft. Note that this issue didn't exist on my copter with the previous fw version 2.7.2.
Here is a graph of the yaw behavior. Notice that the Yaw IN (green) line at the bottom left of the graph is high as I arm the APM. Then around "Line" (x-axis) 520, when I actually take off, the YAW immediately starts falling, although my yaw input (YAW IN) is at zero.
Has anyone else had a similar experience with their tricopter/multi-rotor helicopter and the Ardupilot-Mega platform? Could it be that my servo angle is not correct for the middle stick position?
Any insight would greatly be appreciated.
Thanks!
Hardware details:
Multirotor type: Tricopter
FPVManuals Frame, with wood booms.
APM 2.5
Hobbyking 2830 1100kV outrunner motors (discontinued)
10x4.7 props
Turnigy TGe 9g Micro Servo on the tail rotor
Replies
If the problem is increasing over time, wouldn't that have to be an Integral (PI) problem?
I would bet this is a problem with the mechanical setup and/or PID tuning.
What are your values for Yaw Stab PI and Yaw Rate PID?
I'm flying that same frame with an APM2 FC and FPVManuals motors and have not seen this problem. I recently upgraded to 2.8.1 and found that after the upgrade the frame was a lot less stable in LOITER and AUTO modes (it seems to bounce around a bit). Yaw was twitchy and had a jerky response. I'm assuming I can get rid of that with some tuning. So far (maybe 8 batteries worth of flights) I haven't seen your problem.
When you have the motors running, but the craft is not quite off the ground, is your tail servo keeping the rear motor perfectly flat? Does it start to pitch over time?
Did you do a compass recalibration after loading the new firmware? (You need to).