I have Vex Robotics Kit. I built a 4WD skid-steer robot like the Tumbler-Bot on the web site at
http://www.vexlabs.com/vex-triplets.shtml Each wheel has its own motor. I tried to follow the instructions on page E-9 but one wheel won't work if the motors are connected to motor ports 2, 3, 7, and 8. If I connect the motors to ports 1, 2, 7, and 8, all wheels work BUT when I want to turn the robot left, the robot turns right, and when I want to turn the robot right, the robot turns left. Please check into this.