URGENT: wheel grinding noise
 

On our robot, during practice we have experienced a problem where when we stop feeding joystick input one of the wheels twitches and makes a grinding noise (gearbox grinding) before stopping. It didn't have a this problem before and it's running the same code as it was before. Mechanical insists it's programming issue. Any help is appreciated.

Re: URGENT: wheel grinding noise
 

Mechanical always insists its a programming issue ;) What are the lights on the motor controller doing? Are you doing anything differently when driving than you were before? Are you positive no code changes were made?

Re: URGENT: wheel grinding noise
 

I believe your best bet is to ask some of the teams at the San Diego Regional (the one you are at) for some help. A few that come to mind are 987 and 1538. They should be able to help you troubleshoot and identify the problem and possible solutions.

As a mechanical person, it sounds like a mechanical problem (programming has very little control over grinding). Have you check the gears for proper engagement and alignment? Did you grease the gears at install? Are the motors hot? There are many potential issues, but without knowing more and seeing or hearing the problem it's hard to tell.

Re: URGENT: wheel grinding noise
 

Does the grinding occur when the robot is disabled? If it does, it's definitely mechanical. Otherwise it may very well be programming. Maybe the joystick doesn't return exactly to 0 when you take your hand off it? Try deadbanding the input or using a different joystick. You could also try calibrating your speed controller.

Re: URGENT: wheel grinding noise
 

The wheels twitch for a bit before settling when we stop input.
By twitching I mean the wheels run back and forth at high speeds

Re: URGENT: wheel grinding noise
 

I have experience a phenomenon where the wheels runs without input. Check the dashboard and make sure the joysticks are set to the right usb. Check your code if you have something that takes control of the drive from the joystick. Maybe calibration on the speed controllers are wrong. Run it live and probe the outputs. Could be the joystick, so check on the windows gamepad settings to check if the joystick returns to the center.

Re: URGENT: wheel grinding noise
 

Do you have encoders with speed or position control running? If there is slack in the drivetrain, the control algorithm has trouble making small adjustments because of the lag between its input and a response of the encoder.

A possibly related odd thing I saw yesterday on a robot was a frame short that caused 6V drop, a breaker trip, and then it would repeat at about 3Hz even when the joysticks were centered. They kept working on the isolation of the motor output wires from the frame and also changed out the Digital Breakout and the issue went away, but I still don't entirely understand what was restarting the cycle.

When it is glitching do you have any diagnostic messages, any large voltage drops, any other symptoms that occur at the same time/rate?

Greg McKaskle

Re: URGENT: wheel grinding noise
 

We just said "screw it" and scrapped CANBus, because no other teams were dealing with CANBus and Labview, so we went back to PWM.
Reminder to self, no more Mecanum drive.

Re: URGENT: wheel grinding noise
 

So I know you said it was gearbox, but I just wanted to bring up that it could easily be bearings. Our bot started making a clicky/grinding sound and it turned out to be a bad hex bearing.

Re: URGENT: wheel grinding noise
 

It was a code issue. It was grinding because the wheel was getting an input from something (still haven't figured it out), and it would twitch back and forth, making a grinding noise.

Re: URGENT: wheel grinding noise
 

Alright, glad you got it working.

Re: URGENT: wheel grinding noise
 

Priority 1 is always safety.

It sounds like you do (did?) have encoders with a PID loop (running on CAN Jaguars) on the wheels that is marginally stable due to slack in the mechanical system. Removing the slack (tighten the chain) will help. Closed loop systems have trouble with non-linear delays. This is one reason many Mecanum systems are direct drive. We also square our joystick inputs [ joy * abs(joy) to preserve sign] to improve drive-ability and reduce the sensitivity to the joystick returning to center.

So one mechanical tweak and one software tweak. Closed loop systems are fantastic when they work and adapt to changing environments well but tend not to fail gracefully. Keep pushing your bot (and your team) to higher levels of performance. It does show on the field.