Vex Robotics Design System's Inventor's Guide

Wheels, continued

Friction
Friction occurs everywhere two surfaces are in contact with each other. It is most important when considering the wheels for your robot, however, because you will need to decide how much of it you want in order to maximize your robot’s performance.

Wheel friction has both positive and negative consequences for your robot. On the one hand, friction between the wheel and the ground is absolutely essential in getting the robot to accelerate. Without friction, your robot would spin its wheels without going anywhere, like a car stuck on a patch of ice. Friction between the wheels and the ground gives the robot something to “push off” of when accelerating, decelerating, or turning.

On the other hand, wheel friction is also responsible for slowing your robot down once it is moving. A robot running over a sticky surface will go slower than one running over a smooth one, because the friction dissipates some of the robot’s energy.

Terrain
On more difficult challenge courses, there will often be physical obstacles that must be traversed. Both the size of a tire and the amount of friction it generates will be very important in ensuring that you can successfully navigate them. These obstacles will be numerous and complex, so you will need to plan for them, and test your solutions to make sure that they work reliably.

Clutches

Clutches
Every motor in the Vex Starter Kit comes with a pre-attached clutch module. The clutch module’s purpose is to prevent damage to the motor’s internal gearing by temporarily breaking the connection between the motor and its attached wheel or gear whenever there is too much resistance. This prevents the motor from entering the potentially damaging stall (motor can’t turn) or back-driving (motor is being forced backwards) conditions.

The motor clutches are removable for maintenance reasons, but should always be replaced immediately afterwards. Do not attempt to operate the motors without the clutches installed.