The Vex Robotics Design System is designed to be usable in a competition setting with multiple robots on the field together at the same time. The transmitter's frequency module and the matching receiver crystal determine the control frequency for a robot. Each robot operating at the same time should be on a different control frequency. There are 2 different kits, A and B, giving you a total of 8 more possible control frequencies.

Each Kit gives you a total of 8 crystals- 4 different channels, each one with a crystal for the transmitter and one for the receiver.