Tricopter wobbles a bit coming down from altitude

My tricopter flies great, as in really great.  I do have a question about coming down from altitude.  When I cut the power down (in stabilize mode) to ¼ throttle or so, the tricopter tends to wobble a bit and I can hear the motors trying to stabilize the aircraft during decent. 

The APM2.6 is doing its job of keeping the system pretty level, but it does often get shaky until I apply power again.  If I cut power very slowly it will come down slowly and more evenly, but if I want to come down fairly rapidly, it will wobble a bit.  Is this fairly common?  I certainly wouldn’t just chop the throttle, but it seems like it ought to come down without getting a bit wobbly.  Any ideas?  Thanks, james

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  • Moderator

    Problem with rotor craft is that while descending your props go through their own highly turbulent downwash causing the wobble, increasing the Rate_I term (which corrects errors over time) usually helps.

    I have my Rate_I set to double the P value which also makes the craft very stable and firm in flight, with a low 'I' term if you had to hang a weight on one arm the craft will tilt in that direction, with a high 'I' term it will attempt to correct for the weight and keep flying level so it helps for CG errors too.

    Otherwise fly forward while descending so the props descend ahead of their downwash.

  • I had the same issue on my hexa in stabilize. Going down faster = faster woobles. Down slowly ok. I some circumstances, it was even impossible to regain stable flight when the copter was too low after fast descent and I had a minor crash (4 props,a motor base plate, some gimbal alu arms). All repaired in two days though.

    I lowered the I term in the PID a tad in Rate Roll and Rate Pitch (I think it was from 0.020 to 0.018; don't remember if also in Rate Yaw or not) and tested different descent speed: everything's fine.
    Worth a try.

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