Answered: Gradual loss of motor power.

Our robot has been working great all season, but in the last two weeks some of the motors connected to the robot’s wheels have been failing. We have an H-base, with 4 motors individually connected to 4 wheels for forward/back movement, and another motor/wheel for strafing. The strafing works fine, but starting around 2 weeks ago about a minute into some (not all) matches one or more motors would stop working. If left for a while they would work again for a very short time, then stop again. Also, if the robot is picked up, they run fine, but not when they are on the ground. At first, it was only during competition control, we could do lots of testing without any problems, but now it has gotten to the stage where a few seconds after starting driving, the motors die, starting with those on the left. We’ve tried different motors, both high strength and normal motors, different cables, y-cabling the sides and not y-cabling them, and different ports, including the 2-pin ports on the cortex, with no change. The motors are spread evenly across the motor ports (eg 1,2,9,10)

Does anyone know how to fix this?

**What you described indicates Motors that have failed. When Motors overheat they can trip internal or external resetting breakers. When the Motors cool down, the breakers will reset and then the Motor will work again. The Motors can become damaged from overheating and will no longer function as new ones. Replacing the Motors should have temporarily fixed the problem until they become damaged. You should look at changing the load on the Motors via Gearing or adding Motors to reduce the load per Motor. **

We had the same motors for a few months, but after the problems began, we changed them, and the new ones failed instantly, even though they had had almost no use ever before. The weight of the robot has not changed in a long time. We touched the new motors to see if they were overheating, and they were cold.

You might try measuring the current going to the motors you are having issue with to see if that gives you a clue. Also does the robot drive forward and reverse ok if that is all you did. Now try constantly turning the robot, is this when you have problems? If so, your design may be such that there is too much friction for the drive train to overcome. This will vary based on the surface you are driving on – it is much harder for a robot to turn on carpet than on smooth concrete.

Thanks for your help, the problem was mechanical. It appears a screw had fallen off the robot when someone was testing it, with had allowed the wheel’s shaft to dig into the frame and cause friction.

Glad you found the problem!