Octocopter spins with no stick input

I have a DJI S1000 octocopter powered by a Pixhawk2 running APM 3.4.6 and Mission Planner 1.3.48. When I take off in Stabilize mode, the copter starts to spin constantly on the yaw axis with no yaw (stick rudder) input. The compass has been recalibrated many times and appears to be working. I ran an experiment where I just gave it throttle with no yaw, roll, or pitch input from my RC controller. Even with this, the copter inherently spun.

Examining the dataflash log from this experiment, I have the attached plots. The first image below has the desired yaw and actual yaw plotted. As you can see, the yaw follows the desired yaw so I have concluded it is not an issue with the controller itself since the controller actually does a good job of matching the desired yaw. Note in this plot that desired yaw is changing even though there is no stick input.

Desired%26ActualYaw.png

The second plot shows that the desired yaw changes with a neutral input on RC4 (rudder/yaw). The red line is RCIN. You can see the peak at the beginning is the arming it since you can do that with the RC controller. Then it flatlines before being disarmed. Essentially, with this red line you can see we didn't give it any yaw commands, yet it still yaws as you saw in the first plot of desired and actual yaw. 

RCIN%26RCOUTchannel4.png

I see similar behavior in LOITER and ALT_HOLD modes.

Does anyone know why the desired yaw changes with no stick input?

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  • Worked it out in another thread for anyone wondering Link to other thread with solution

    Octocopter spins with no stick input
    I have a DJI S1000 octocopter powered by a Pixhawk2 running APM 3.4.6 and Mission Planner 1.3.48. When I take off in Stabilize mode, the copter start…
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