I cannot really tell what the problem may be without more specifics.... but you need to check and make sure that your joysticks are o.k...... you can try this by swapping them around to see if the problem follows one or the other. You also need to make sure that your joysticks/speed controllers are 'calibrated'.... sometimes you need to adjust the wheel on the base of the joystick until the LED on the speed controller is steady on. It will turn green or red whenever you are trying to control the motor in a positive or negative position. Check the breakers and fuses to make sure that nothing is burned out or tripped. You can also try to swap speed controllers, if that is what you are using.... and make sure that you have the right PWM channel going to the right controller.... it is easy to think you are on channel "x" and you're actually on channel "y"....
If you go through each of these possibilities and it still doesn't work, e-mail me directly:
christine.q.powell@nasa.gov
Good luck!
Christine