Wobbly P3

[crookshack]

Hello everyone. I'm brand new here and hope I can get some help from you knowledgeable people.
Yesterday, I was distracted when my drone wandered into a tree at a height of about ten feet. It crashed and the battery popped out. I brushed it off and reinstalled it and fired it back up. Now the thing wobbles something fierce. After calibrating everything, there was no change. There is no play at all in the motors and the prop shafts don't appear to have any runout. I let the bird idle on the ground and checked to see if there was any noticeable difference in rpms in the motors. One did seem slower and maybe two did. So, with it still in idle, I would push the right stick full left and right as if I were flying left then right. The motors on the right side spun up a fair amount faster than the left ones. I have taken it apart and don't see anywhere they could be binding and there are no loose wires inside the bird. The motors all turn by hand with about the same resistance. It's really hard for me to believe that the motors are at fault but I'm not sure. I don't know what to try next. I really can't afford to send it in for an expensive repair. I got a good deal on it refurbished for $297.00. and I figure it might cost that much to get it fixed by professionals. Any suggestions would be greatly appreciated. Thank you.

 

[telfish]

Are any of the props damaged, do you have a spare set to try?

 

[crookshack]

Are any of the props damaged, do you have a spare set to try?

Wow! That was quick. Yes, I replaced all the props with new ones.

 

[telfish]

OK. So I would re calibrate everything that has that option and see if that makes a difference.

 

[crookshack]

OK. So I would re calibrate everything that has that option and see if that makes a difference.

I've already done that.

 

[telfish]

Fresh out of ideas.

 

[crookshack]

Fresh out of ideas.

Thanks anyway.

 

[Jayfdee]

Could be the ESC's on one or more motors, no idea how to test them, but if you can borrow a Tacho from somewhere, measure the speeds on tickover.

 

[crookshack]

Could be the ESC's on one or more motors, no idea how to test them, but if you can borrow a Tacho from somewhere, measure the speeds on tickover.

Thanks. Are the esc replaceable individually or would that mean a whole board replacement if that is the problem?

 

[Jayfdee]

Thanks. Are the esc replaceable individually or would that mean a whole board replacement if that is the problem?

Whole board unfortunately. On further thought, if it was an ESC error, then I think it would be reported on the app.
My old P2 used to burn them out for fun if I hit a tree or jammed the motor, but they were simple to replace individually.

 

[crookshack]

Whole board unfortunately. On further thought, if it was an ESC error, then I think it would be reported on the app.
My old P2 used to burn them out for fun if I hit a tree or jammed the motor, but they were simple to replace individually.

I can get new motors pretty cheap. I think I may go that route first. Thanks again.

 

[N017RW]

You cant tell anything by tach-ing the motors at idle.

These are fly-by-wire devices with motor speeds controlled by the MC in which they vary constantly in-flight to maintain flight request and stability.

 

[Nightwolf]

Motor alignment?

 

[Jayfdee]

You cant tell anything by tach-ing the motors at idle.

These are fly-by-wire devices with motor speeds controlled by the MC in which they vary constantly in-flight to maintain flight request and stability.

Surely at idle on a level surface, with no stick inputs, the motors should spin at about the same speeds. The OP mentioned he thought there were some discrepancies. I cannot imagine that at idle, and the AC not moving, there is a control algorithm running that is altering the speeds.
I have never noticed my prop speed varying at all at idle.
Just me observing and speculating.

 

[N017RW]

Ok, about. But that's kinda vague.

There's no guarantee that the motors ever spin at same speeds.

 

[Brother Dave]

Can you upload a video of the wobble?

 

[Brother Dave]

Photos might help, too. Some of the guys notice the smallest imperfections.

 

[Jayfdee]

Ok, about. But that's kinda vague.

There's no guarantee that the motors ever spin at same speeds.

Ok, about. But that's kinda vague.

There's no guarantee that the motors ever spin at same speeds.

I used the word "about" deliberately because each motor is individual, and friction in the bearings and other factors affect the speed. There is no feedback of motor speed to the control system, it is not measured, so the control system does not try and maintain a particular speed.
The control algorithm feedback loop is from GPS, accelerometer, Gyro, VPS etc, so I maintain, that at idle, on a level surface, with no stick inputs, the motors should spin at about the same speed, and this is good enough for diagnostics.

 

[crookshack]

I took out the suspect motor and oiled the bearing. After getting it back together I turned everything on to try it. Then I get an "IMU preheating msg, which since I've had it it's never done that. (It's about 80 degrees F here today). Any way after it was clear, one rear led is was blinking yellow and the other red. After a little bit the red one went off and only the one side still had the blinking yellow. I have looked at the code chart in the manual but I'm confused. I figured the blinking patterns would at least be the same on the left and right. When they are different, I don't know how to interpret what it means.

 

[N017RW]

I used the word "about" deliberately because each motor is individual, and friction in the bearings and other factors affect the speed. There is no feedback of motor speed to the control system, it is not measured, so the control system does not try and maintain a particular speed.
The control algorithm feedback loop is from GPS, accelerometer, Gyro, VPS etc, so I maintain, that at idle, on a level surface, with no stick inputs, the motors should spin at about the same speed, and this is good enough for diagnostics.

The ESC receives back-emf from each motor phase to enable commutation, thus it absolutely knows the speed of each motor.