Motor drift

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hberg
Posts: 4
Joined: Sat Sep 24, 2011 7:37 pm

Motor drift

Post by hberg »

Hello,

when i don't attach any ESC, set everything to exact 1500, disable ACC, i get some strange drift from several motors:
motor_problem.png


FRONT_L and REAR_L are about 200 values above the other two motors.

When everything is nearly exact 1500, shouldn't be the acceleration of the motors exact the same?

I did this:
Power MultiWii Board
Connect FDTI Cable
Power Receiver
Disable ACC
Throttle UP and DOWN - motor values are equal
ROLL to LEFT and then back to exact 1500 - motor values not eqal (picture)
the same with ROLL to RIGHT, but NOT with YAW.

hberg

cardboard
Posts: 183
Joined: Tue Mar 15, 2011 9:40 am

Re: Motor drift

Post by cardboard »

If I am not mistaken this is to do with the I term in the pid loop. When the copter is in free flight, (not supported by your hand/ a desk) this value is self correcting resulting in balanced flight. I think if you were to power everything up and get it to hover whilst plugged into usb you would notice then that the motors would put out more even values.

hberg
Posts: 4
Joined: Sat Sep 24, 2011 7:37 pm

Re: Motor drift

Post by hberg »

Ah, then thats what Alex meant:
The motor output on the GUI is not equal on both sides with a neutral RC input

This is the normal PID loop behaviour, the I-term is actually cumulating the error over time & tries to compensate for that but the copter is hand-held or fixed on the table.
When the I-term is zeroed, the this will not happen.
A flying multicopter will actually use the I-term in the PID to correct itself again to the same level as before the disturbance.


I had a problem with the stabilization of the copter, and i thought, when the motor values are some how stuck or drifts apart, there is no chance to get it stable. But now i know, it was just my mistake and i need to learn how to fly :).

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