Hey,
Our team is having a problem where the whole robot disconnects and stops moving for a few minutes. 8 turbo motors are on the drive and there is no power expander. I tried doing some research and found this thread: https://vexforum.com/t/8-motor-turbo-base-overheating/45088/1 Are the motors overheating? How much would a power expander help?
That’s the likely culprit. Overheated motors slow down just before they die entirely, but if you have those motors are geared, you might not notice that. a power expander wouldn’t help since power isn’t the root of your problem. You likely have the motors trying to make wheels move faster than the motors can handle for long periods of time.
You might find that reducing the gear ratio… going back to the High Speed gears, for instance, will not only address your overheating issues, but also make your robot faster.
It seems weird, but keep in mind that the effective speed of your robot is how long it takes to get from point A to point B. Most of that time, for short sprints, is in acceleration and deceleration. In these regions you aren’t using the maximum RPM of your motor outputs… you want maximum torque.
You can also look at the motor power curve… you get your maximum power output from your motors at about half of their free (unloaded) rpm. So with your turbo gears you have to get the motors up to (about) 120rpm before hitting peak power, but with high speed gears you’ll hit peak power around 80rpm. You’ll probably spend much more time in your “power zone” with the lower gear ratio.
Good luck solving the problem. Remember that the “fastest” robot is rarely the quickest robot!
Jason
make sure you split the motors evenly - we have 4 up top and 4 on the bottom, half left and half right drive for each. There was one time where one port on the bottom broke, so we moved it so that 6 motors were up top and 2 were on the bottom - that bank stalled out very fast.
edited for clarification
Ideally you want to offload at least two of your drive motors onto the power expander to better distribute the power draw since all 8 will be running simultaneously. I’ve fried a cortex by trying to power 8 turbo drive motors directly.