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AC3.5-rc11 Oscillation/instability from motors 3 and 4

pixhawk

(Justsomeguy1983) #1

I just flashed AC3.5-rc11 on my quad, I’m running a pixhack with 4006-380kv motors, hobbywing 40a xrotor escs with the latest blheli spinning 15" props. After flashing AC3.5-rc11 I re-calibrated everything including ESCs.

When I begin to take off in stabilize the air frame begins to oscillate back and forth a few degrees 45 degrees off of the longitudinal axis. (It’s and X configuration) And you can hear a couple motors sort of “pulsing”. I’ve tried to reduce the roll/pitch rate control slider, and It didn’t make much of a difference.
I made some investigation in the logs. The pwm from the flight controller on RCOU, channels 3 and 4 indicate the oscillation, and, they are 180 degrees out of phase from each other, which explains the kind of rocking motion the airframe does between motors 3 and 4.

The oscillation isn’t terrible but, I certainly don’t feel comfortable flying this way. I’m too nervous to do a autotune either.

Any advise is greatly appreciated as I don’t know what my next step should be.
Bin Log Here
Thanks!


(Matt) #2

What version were you running before? RC11?


(Justsomeguy1983) #3

3.4.6 I believe. The latest stable release.


(lucamax) #4

IMO wrong esc calibration, try to calibrate esc by BlHeli suite software.


(Justsomeguy1983) #5

Okay. Well. I guess I’ll re-cal ESCs and give that a whirl.

Would reducing the ATC_RAT_RLL_FILT, ATC_RAT_PIT_FILT parameters effect this at all? I am running >13" props…


(rmackay9) #6

justsomeguy1983,
I’d recommend leaving the filter values at their defaults. It’s the Rate Roll P, I and D and Rate Pitch P, I and D gains that should be changed.


(Justsomeguy1983) #7

So just an update here, I cranked the PIDs down to near minimal ranges, and was successful in utilizing the autotune feature. My oscillations are now non-existent!

BTW, that position hold-autotune is impressive, I could ave gone airborne, flipped into auto and taken a 15 minute nap.

Thanks for the great work, Devs.