See video here: FRC 9237 Drivetrain Grinding - YouTube
We are using the kit chassis from andymark. When we turn left, everything is smooth and quiet like I would expect. But turning right, both sides of the robot sound like gears are grinding and the whole robot jitters.
We’ve avoided driving the robot any more than this to avoid potential damage.
Any ideas as to why we are experiencing this would be appreciated!
Can you post code as well just in case that is the problem?
We were getting chatter like that (and worse) with a kitbot running four NEOs–we finally (after burning out three NEOs and taking apart/replacing gearbox elements over and over again) isolated the problem to a bad SparkMax controller causing the motors to go haywire (and in one case seizing altogether and bursting forth with a plume of smoke).
Unfortunately I’m not involved with that side of things.
Is there an easy way to tell if the spark is bad or not?
A little more information: I pushed the robot by hand in all directions, turning and forward and back and I got none of the grinding sounds.
Test the direction of each motor one at a time.
Pull your breakers from the drivetrain and add them back one by one, making sure to test each motor on each side individually. If you push your joystick forward and one motor makes the wheels move backwards, you have conflicting motor inversions.
This can of course also be checked in code. I recommend you solve this with your programmers.
That’s a theory based on you stating there were no sounds when you moved things by hand (assuming the robot was off)
Also make sure all motors are either in brake or in coast. They should all be set the same.
Edit: Are you controlling this in arcade or tank? I see you’re not a mentor new to FRC so you may have already checked what I stated above.
Out of curiosity, what speed controllers are you using and how are you controlling them (PWM vs CAN)?
If you’re using PWM, there’s a small chance the issue could be electromagnetic interference related (twisted CAN wires shouldn’t have this issue). I’ve seen at least one team have weird issues with PWM controls that were completely solved by putting ferrite cores around the PWM wire ends.
Beyond that, as other’s have said, test motors one at a time and check that the direction of rotation is correct for each one (including when turning. Since it only happens when turning, it’s unlikely to be a gearbox issue. The only other mechanical thing I could think of is that side-loading on the wheels due to scrub turning turning might be causing wheels to rub on something if the chassis wasn’t assembled properly.
Yes I’ve already tested each drive motor one at a time. No conflicting directional movement. That was one of my first thoughts.
Unfortunately I was on my way out when we discovered this so I haven’t been able to troubleshoot much more than that.
Check that all the screws holding the pulleys onto the wheels are all the way in. If one sticks out, it might clear the adjacent plate until there is a side force from turning.
We had some back out because they were over-tightened when first installed.
We pulled the drive motors (like, a gazillion times) and ran them free-spinning. One exhibited behavior that was Very Bad Indeed™. We swapped which motor was connected to which SparkMax, and the other motor exhibited behavior that was Very Bad Indeed™. We swapped out the SparkMax for a new one, and both worked fine.
Update:
The chassis only makes the grinding sounds when on the floor. We put the robot up on blocks tonight and the sounds went away.
This appears to be a 2022 kit chassis. They had a known problem with the provided screws that cause them to work out, not caused by over tightening. This isn’t a problem present on 2023 or 2020 and prior chassis.
The photo I provided was of our 2022 chassis after the “bad” screws were replaced with the proper screws. When I tried tightening the screws, they just spun with little pressure, indicating the plastic in the wheel was stripped.
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