We are a first time VEX team, and we are having some serious issues with our drive train. We originally powered a back wheel and had an unconnected front wheel that always seemed to work until we finished all the other components. Once we put the robot on the ground, the wheels would lock up and not move. We tried connecting the front and back wheels with a gear train, but got the same result. Is it possible for the weight of the robot to be too much for the motor to handle? I’m still quite puzzled as to what exactly is happening to make it lock up as much as it is. We are quickly running out of time and are wondering if there is any tips for building a drive train to handle weight more efficiently. Is there anything we are overlooking? Thanks.
Depending on the weight of your robot, a two motor drive train could definitely be too little motor power. To increase the efficiency (and weight handling abilities), here are a couple things to consider:
Make sure your axles are straight. Bent axles cause lots and lots of friction.
Make sure that your axles are connected to the structure correctly. (i.e. bearing flats so the axle doesn’t rest on the metal as much, make sure collars aren’t pressing too tightly against the metal)
Make sure that your axles are correctly supported. If your robot has weight problems, connecting the axle on only one side is not a great idea.
Other than that, you might have to add more motors to your drive train. Two motor drive trains usually only work on very light robots, and even then fail frequently when subjected to too much pushing.
On our robots we have usually had four motor drivetrains and that works out just fine. As he said do you have bearing flats on the axles?
- make your robot lighter
- gear your robot down (slower)
- use more motors
- use omni wheels if you have some
Yes, we are using bearing flats, so that’s not it. I am guessing we need to put in a 4 motor (or 6 motor maybe) drive train for there to be any hope. Any tips for this? And unfortunately, no omni wheels for us (didn’t come with the spare POE kit we are using/mooching off of).
Thanks for the answers by the way. We are really running low on time (2 days left 
) and only have 2 people, so it is great to get some help. Luckily it seems everything else is working and near complete. Now hopefully we can make it move :P.
If you decide to go with 6 wheel drive, you might have a problem with wheels overlapping. If you are using larger wheels, and your drivetrain is not fully 17.5 inches long, the wheels might not fit in the same plane. The common solution for this is to bump the center wheels in toward the center of the robot and the outer wheels toward the outside so that they are staggered.
If you are using 269 motors then try using 369 motors.