Rover - acro mode shaking

ArduRover
1

I am having issue with tuning turn rate on my rover with Pixhawk cube orange and Cytron SmartDriveDuo MDDS30 - ESC MODULE. It keeps oscillating when stationary but when moving or turning on command in acro mode - it behaves well. It drives straight without yaw input and turns OK. I tried setting FF to 0 or minimal value without improvement. Setting P and I to 0 resolves oscillation but if I change it even to 0.0001 - it starts doing it again.

What is more in guided, manual and hold servo output for motor pwm is 1500us. when switching to acro -motor pwm is wobbling between 1460-1560us - instantly, witchout any reason rover is still.

Of course i can set MOT_THR_MIN below motor treshold value, but why this is happend ?!?

Here you can find my logs: rover - Google Drive

Any advise? @rmackay9

Thanks.

2

Enable the ARMING_CHECK to 1, so we can see if there are any issues

It could be that the steering’s reversed. Try setting SERVOn_REVERSED for your outputs, or swapping the left and right outputs.

3

It drives well in any mode, problem is when it’s standing in place . When You switch to ACRO it motor pwm is changing between 1460-1560us - instantly, without any reason . Switch to manual,guided it holding on motor output 1500us while standing.

More:
on pid chart where piddesired plot is constant the pidachived is wobbling alot ( but why?- this is the question)

I guess it could be problem witch EKF3 or some kind of filter or noise settings ?

4

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5

Could be that your throttle isn’t centered at the RC trim position, and it’s trying to move very slowly but can’t.

Check RC calibration values and center all trims.

6

there is no RC just MP. probably this is common problem. I saw same behavior on @rmackay9 s wiki video about tuning steering rate. Like iI described swiching to ACRO cause instantly input +/- 50us values- whithout any outside input. Can ridd of wobbling by setting MOT_THR_MIN 2-3 % below phisical minimum, sets PID near 0, set DZ to motor, set MOT_THR_EXPO -0.3 and more.
More importatn is that turn controler is Wobbling by iself on start and it could be a couse of future problems

7

@Mogway28,

A log file will help, much better than pictures, but in any case, also make sure the autopilot is somewhat near the center of the frame.

8

Here you can find log file: rover - Google Drive

9

Hi @Wiktor_S,

Sorry for replying to the wrong person above.

I think @Mogway28’s advice is good. Here’s some advice from me which overlaps somewhat

  • reduce MOT_THR_MIN to 3 (currently 8)
  • use MP’s motor test to ensure the motors start at about the same throttle value in both forward and backward directions
  • reduce ATC_STR_RAT_FLTE to 3 (currently 10)

I think reducing MOT_THR_MIN on its own should resolve the problem though

10

You are right - if I set MOT_THR_MIN below 8 or to 3, there is no shaking anymore, but on the graph, I can see the same waveform for pidachieved.

Also, I am worried about motor start because the left motor starts later than the right. I tried to change the servo trim but without any good result. Is there any option to force simultaneous start for both motors?

11

If you switch to ACRO, motor pwm is changing between 1460-1560us - instantly, without any reason. In my opinion that is reason of not simultaneous start. But maybe you know the real reason of output PWM uneven value.