Motors are rotating at differnet speeds

We are competing in Vex Sack Attack… We have our robot built but are having some problems. We have 2 wire 393 motors on each back wheel and the omni wheels up front. For some reason the left rear motor keeps cutting out and not the back right motor. It seems like the left motor is going slower than the right. Why would that be and if it is could that be why it is cutting out and not the right motor? I check the programming, they are the same set up on each wheel… We use Easy C… Can anyone help or give suggestions? We run the robot for about 1min 30 sec and let it cool for about 1min 30 sec… It will go for several “rounds” but after that the left motor keeps cutting in and out. I can understand if we are over heating them, but not both motors are cutting in and out…

Thank you,

It sounds like a friction problem, does the wheel rotate freely when the motor is not attached?

How heavy is the robot? Can you post pictures so we can see the design? Does the robot drive straight or pull to one side?


I did end up taking out a large shaft space and replacing it with a smaller one to see if that helps… I will know today around 8th period when the students drive it. I will try and post a picture ASAP…It is heavy, but not any heavier than last years and it was ran off 2 393 motors.It drives straight… No pull to it.


I just posted some to the gallery… If you can’t find it search 4607, North Lamar, Robot

Like I said I am confused b/c it is only one side locking up, not both sides.

So the first thing I would do is eliminate the motor from being the problem. Try swapping left and right motors and see if the problem moves with the motor or stays on the same side. How are the motors configured into the cortex? ie. which ports, are they both on MC29? When you swap the motors leave the port alone, if the problem moves then swap ports and see if it moves back. In other words, you have good access to your motors so eliminate them, the MC29s and the cortex ports from being the problem first.

Sounds good… I understand what you mean by that…They are both on MC 29… Yes sir…I will try that… Thank you for the advice… I appreciate it.