Answered: High Strength Motor Problems

We have four high strength motors hooked up to a cortex powering a drive train we recently built.

After more or less 10 seconds of intense driving, the motors lose strength and the robot essential comes to a complete stop and is unable to move. If I pick the robot up during this halt, the motors spin easily. If I wait around 10 seconds without attempting to drive after this has happened, full power returns for another brief period of time until it comes to a complete halt again. Testing with the PIC microcontroller leads to essentially the same problem as with the cortex, but the motors weakly twitch instead of coming to a complete halt. If I unplug the two motors on one side of the drive, it still comes to a halt in the same amount of time.

We tested this with numerous batteries that had all been through discharge-recharge cycles that we knew were good batteries.

Why is this happening? What can we do?

**I think you are tripping a 4 Amp Breaker inside the Cortex. If more than 4 Amps flows through a Breaker for very long, the Breaker will trip and open. When you wait for 10 seconds, you are allowing the internal Breaker too cool down and reset or close, thus your motors start working again. Now that a Breaker is somewhat hot, it will trip sooner with the same load applied.

To keep this from happening, you must reduce the current load through the Breaker. Each Motor Port 1-5 share a 4 Amp Breaker and Motor Ports 6-10 share a 4 Amp Breaker. So if you have all of your motors connected to Motor Ports 1-5, moving some of them to Motor Ports 6-10 will help. You can also vary your “gearing” to change current load on the motors. You can also add a Power Expander with a battery. The Motor Ports on the Power Expander also share a 4 Amp Breaker. **

We did spread out the high strength motors to use ports 1, 2, 9, and 10, but we still encountered the same problem at our competition yesterday during every match that we played. We tried offloading two of the high strength motors to a power expander, but that caused the breaker in the power expander to trip FASTER… So we just had to take them off and rebuild our robot.

Another team (3057) was at the event and was also using high strength motors on their arm, and they tripped the internal breaker just about every time they attempted to move their arm.

Any new ideas?

I believe this is still a matter of current. There is also a resetting Breaker inside the Motor. You should be able to pull a little over 1.5 Amps through a High Strength Motor for a couple of minutes before the Motor’s internal breaker will trip. You may be tripping the Motor’s internal breaker and not the one in the CORTEX or maybe a combination of both.

I believe everything else on our robot still functions when our base stops… which would point to the breaker on the motors being the problem?

If you have other Motors that still work when your base stops, then yes - it would be the Motor’s internal breaker that is tripping. Only the Motor Outputs are affected when the Cortex internal breaker trips – everything else on the Cortex would still work when a breaker internal to the Cortex is tripped.