VEX v5 Drivetrain Issue: Sudden Speed Drop at Top Speed
Hey everyone, I’m encountering a strange issue with my VEX v5 drivetrain and I’m hoping someone here might have some insight.
The Problem:
My robot runs perfectly fine at all speeds, but when I set it to full speed, it runs for a couple of seconds and then suddenly and abruptly drops down to a much slower speed. It doesn’t stop completely, it just slows down significantly and stays at that reduced speed until I stop and do it again.
What I’ve Checked So Far:
Battery: I’ve fully charged my battery, and the issue still occurs.
Motors: The motors aren’t hot or making any weird noises.
Code: I’ve simplified my code to just a basic drivetrain command to rule out any other programming errors.
I’m using the VEX v5 Brain and the VEXcode v5 c++ software in vs code . Has anyone experienced this before or have any ideas what might be causing it? Any suggestions would be greatly appreciated!
You can try gearing the drivetrain down a bit or swapping in torque cartridges instead of speed ones, since the motors are probably hitting their built-in current limit at full speed. Also make sure your battery is healthy, because even a “charged” battery can sag under load and trigger the slowdown. If the issue only happens when the robot is on the ground, check for extra friction or binding in the wheels and shafts, since that extra resistance can push the motors into protection mode.
I did some more testing and the moment the robot’s speed drops, the current draw from the motors suddenly spikes from 0.6A to 1.4A. This happens on all six drivetrain motors simultaneously.
How many motors do you have on your drivetrain? I’ve seen this happen on six-motor drivetrains when something is going on with one of the motors (wrong port? bad connection? bad motor? ) I don’t remember specifically which problems cause it. I also don’t know why it behaves that away; maybe it has to do with the EMF generated by the misconfigured motor. Anyway, you could test this by plugging in just one drivetrain motor at a time and make sure each one individually makes its side of the drivetrain go the correct direction.
Hello, we had that same issue. What rpm and motors are you using? We used a 55w drivetrain, and discovered that the 5.5w motors weren’t matching the speed that the 11w motors were running. So if you are doing 450rpm like we did, you will want to gear those 5.5w motors to match the other ones.
