Drivebase losing power.

Hello all!

Recently at a competition, our drivebase (4 motor torque tank direct drive) was working fine for the first 8 qualification matches, and all of the practice matches beforehand. However, when we entered the elimination matches, one side of the motors would lose power. They hadn’t stalled out, because they still managed to go at a relatively slow speed, but they didn’t give us any pushing power while the other side was completely fine.

No idea why it would happen, and it would also show up in the autonomous: Our robot had a tendency to head towards the right (the side with the slowing motors). The motors still drove forwards, but didn’t necessarily do so at full speed. Our robot is very light (all aluminum, just the mogo carrier).

Thanks all!

I’d double check your motor controllers.

If you take the robot off the ground and run the wheels, you can compare their speeds and torques. (If one or two don’t work, figure out the problem.)

The problem is, I’ve never been able to simulate this, and it only happens in autonomous and maybe the last ~30 seconds of a match.

So, the robot works perfectly any other time?

If so, I have no clue what your issue could be

The robot works perfectly fine even when I drive it for 5 minutes straight, pulling another robot, pushing another robot, etc.

It just randomly decides to…not go?

Thanks anyways!

It could just be one motor tripping, slowing it down but not totally stalling. Disconnect the shafts from the motors and spin the wheels to compare friction. You might also have a bad cable. The copper wire inside could be frayed so that when disturbed it loses connection. I doubt this, but it would maybe explain why it only happens in matches; that’s when your robot is under the most extreme forces. I doubt that this is the case, but a visual inspection of all of your cables to make sure they aren’t being pulled taut or kinked could be worthwhile.

This does sound like a motor stall, or maybe an intermittent wiring issue with one motor.

Try again to reproduce the issue. Otherwise, you won’t know if it’s really fixed.

What is different about the competition field and your practice area? On a real field the foam tiles provide a lot of traction. This makes turning more accurate, but is also harder on the motors, especially if you have rubber wheels. Are you practicing on a high friction surface?

Another thing that causes a motor stalls is getting the robot stuck in the corner on the scoring bars, and then fighting to get out. The robot might not stall while this is happening, but it contributes to overheating the motors which makes them more susceptible to stalling later.

During auton are you running the motors at full speed?

It is more than likely a problem with the motor controller I had one that I got through an entire competition fine and then the next week it barely moved. I replaced the motor controller and it was fine

Check your program. If is only happens during autonomous and no other time, even when you’re stressing the motors a lot, it’s probably code based. Double check to make sure all your drive motors are set to the speed you want it to go during autonomous. If only 3/4 motors are actually driving, it will stall very easily.