Unexpected Drive stall!?

So,in last year’s competition we had a major problem with our drive where it would stall randomly in matches and we found a fix which was limiting motor speed. The first competition this year was successful and we did not have any stall issues. Now the problem has come back and we are having the same stall issues. We do not get what happened as our robot weighs pretty much the same, all aluminum dr4b, and we only made minor changes. What do you think the problem is? Also, we are using a power expander.

How many motors? What size wheels? What internal/external gear ratio?

4 motors, 4 wheels speed ratio

How much does your robot weigh? I forgot to ask that first.

We don’t have a weight scale but I assume it’s about 30lbs, though I know that the drive did not stall last competition and its the same weight as it was before

Could be your wiring, check out the thread below!


Well try that hopefully it works. You can put it in any port in the power expander right? 1 motor cortex, 1 motor power expander?

19 pounds is the upper limit of a 4 motor speed drive. You’re bot is way to heavy to run that ratio. You just got lucky at the last comp. Our freshman had luck like that last tear.

Actually it seemed to work, what consequences are there if we continue to run it like it is? {2 days until the tournament}

Consequences? Generally a lack of reliability, and a lack of pushing power. Any time you put increased torque than you would normally trigger the PTC’s in your robot to trip, meaning you stall and are kaput for a short period of time. Of course, you could switch to a torque drive, which would allow you to be much more comfortable and reliable in matches, because you know, a stalled robot scores 0 points.

Ur right as our robot still seems to stall, we tried wiring it having the left drive on the power expander and the right on the cortex but either side or both would just stall during matches. Can someone explain what they mean by doing a y split, as we don’t have a 4 motor lift but have a 2 motor lift and 2 motor chainbar. How should we wire it, as switching to torque is not an option.

A y split is where you use a the Y shaped cable (forgot what it’s called). Plug that into the cortex, then plug motor controllers into that. Then plug motors into the motor controllers. This allow 2 motors to be controlled by the same port on the cortex, and therefore perform the same motions(if they’re geared the same)

Yes but if you y split the drive it wont go in the same direction and that can’t be fixed by the code either right?

Two motors off of a Y-cable will always receive essentially the same instructions from the cortex. However, you can reverse the direction of these motors through wiring. However, as others have stated, a 30-pound robot with a 4-motor high speed drive on 4-inch wheels will consistently stall, regardless of your wiring. That’s all there is to it.

The best thing to do in this situation is if you can’t change the load the motor can handle, after every match, spray it down with either liquid nitrogen or liquid propane (canned keyboard duster) and such, essentially something really cold to put on the motor.

I would recommend the robot go on a quick diet. No matter what wire configuration you have, 30 pounds is too much for four high speed direct drive motors. Not to mention I’m guessing you’re using four-inch wheels which requires even more power from the motors (this would contribute to the “brown out” or stall).

Well last year, we used a 4 motor high speed drive on 4 inch omni wheels for our 32 lb steel 6 bar lift. It was could go fast enough to drop stars and they would roll into the far zone. We were able to do this using slew rate

I know the precise issue here. Regardless of what your motors are geared to, this issue will happen with a power expander.

The power expander has an extra PTC inside it (in addition to the cortex’s two PTCs). This means that if you put all four drive motors on the power expander, your drive will stall. To fix this issue, you might want to put two motors on your power expander and two on the cortex.