My motors are uneven, any OpenROV engineers here?


#1

I’ve just finished my 2.8 build and done a first dive, which went very well and was very exciting.
Strangely, right from the beginning, the port motor is much “stiffer” than the starboard motor. By that, I mean it is more difficult to turn by hand, not friction, but almost as if it is more magnetised. It also starts and stops much quicker, the starboard motor freewheels longer.
If I go into diagnostics and manually set port and starboard motors to the same setting, perhaps 0.008 the starboard is turning much quicker.
I’m worried that it won’t be going forward or backward in a straight line, on the first dive it was difficult to tell.

The up/down motor seems to be as free as the starboard motor. Any ideas? Here’s a video clip of them running at 0.008

IMG_7320.mp4 by ash2020, on Flickr


First dive in the lake of Annecy
#2

A few things that I might try first.

Check and make sure that there is no metal pieces stuck in the rotor or bell. This can cause the problem.

Next, it might not be a problem, try driving the ROV forward on speed 1, 2 and 3 and see if it tracks to the left or right by a large amount.

Z


#3

Hi Zack.
Yeah, mine does turn more to the left when going straight ahead. It’s the port motor that is stiffer and turns much slower for the same current input. I’ve checked and there’s nothing obstructing it. As I mentioned in the original post, it’s not a frictional feel, more like greater magnetism, when you turn it by hand each pole clunks into place.
The starboard motor feels the same as the up/down motor. I’m used to building quadcopters and the motors always have the same feel to them.
Andy


#4

This sounds like a problem with the bearings/shaft collar rather than the magnetism…though it could be…

Last question: This happens when the ROV has not batteries in it as well?

Z


#5

Hi Zack
No, there is no friction in the motor, and it happens with or without the batteries.
If you turn any brushless motor, you can feel the “steps” as each pole aligns. With these three, two of them are fairly small, but noticeable steps, the odd one is a much stronger step to the next pole. That is the only way I can explain it, but it is definitely not friction.


#6

I see…

Would you mind filling out this form here:
https://openrov.zendesk.com/hc/en-us/requests/new

We can try a few things and then post the solution when we find it here in
this thread.

Best,
Z