Power expander battery management.

So my team was at a competition recently and we won skills, got 2nd in teamwork. throughout the day, our 4-motor speed 393 1:1 drive kept burning out and shutting down, so now we are switching to an 8 motor drive, and are installing a power expander. Our team only has 3 competition batteries, so we don’t really know what to d as far as charging batteries between matches. Any help?

Buy at least a fourth battery and make sure you have at least two chargers.

As for why it’s burning out and shutting down, you should probably address why that’s happening, as most reasons I’ve seen that can cause a 4 motor drive to burn out will cause an 8 motor drive to burn out. Those are mostly friction and bad control, bad control being either code or a driver that habitually tries to run the motors at full power and 0 rpm. You can fix both causes of bad control with encoders and clever coding. Friction you have to build out of your system: with the motors disconnected the wheels should spin easily and freely, and the robot should not be excessively heavy.

We have looked at all of those physical elements, we even drilled out a bearing flat when one of them was too tight. We have enough chargers, i will probably propose that we buy another battery next meeting.

P.S. I love vex forum! people respond so fast!

What is your robot built of - steel or aluminum? We are built with aluminum this year and that makes a big difference in our capability. If you are steel, you will most likely need to use torque motors, especially as direct drive. The power expander will help, but like others said, if there are other issues in your construction, that makes a difference too. Look on ebay for some extra chargers and batteries. We were able to pick up a few at roughly a third the cost of new. They test ok with a battery beak as well.

Yes our robot is aluminum.

That helps.

On our robot the girls use an expander and it runs the front roller, the ball conveyor and the two shooter motors (ports 4-7) so those auxiliary functions are on the PTC in the expander. The cortex has the left side motors (ports 2, 3) and the right side motors (ports 8, 9). I believe port 10 has our defense bar (very low load). Nothing on port 1.

Having the extra place to spread out the PTC load really helps.