Vex Robotics Motor Controller?

I have some Vex Robotics Motor Controllers. Either I made wiring errors or they require more-powerful power sources. They won't run the motors when connected to Arduino UNO board. They run when connected to Vex Robotics Signal Splitter using Vex Robotics radio transmitter. How can I fix the problems?

Your diagnoses may well be true. We can't help if you don't show us the setup your using though. Full code + schematic + motor datasheet is a good start.