How to Decide on which VEX Plastic Wheels to Use

A primary function of most robots is moving around. The selection of which wheel to use can be a critical decision and can determine the success of a robot’s design. There are advantages and disadvantages with each type of wheel. The two major factors to consider are the diameter of the wheel (the distance from a point on one side of the wheel to a point directly across on the other side) and the traction of the wheel.

Comparison of VEX Plastic Wheels

The diameter of a wheel (Hub and Rubber Tire assembly) can affect a number of things, such as:

  • Distance per revolution is the distance a wheel will roll with one complete revolution.

  • Footprint is the area created between the points at which the outermost wheels on the robot touch the ground. Typically, the larger the robot’s footprint, the more stable it is and less likely it is to tip over.
  • Ground clearance is the height from the ground to the lowest structure on the robot. A larger the ground clearance will make it easier for the robot to travel over obstacles.

The greater the traction of a wheel, the harder the robot can push or pull, and the easier the robot can travel over obstacles. However, if a wheel has a high degree of traction it is harder for the robot to turn.

Hub/Tire Distance per Revolution Footprint Ground Clearance Traction
20mm Pulley/
100mm Tire
100mm
(3.94 inches)
Large Small Fair
Small Wheel Hub/
160mm Tire
160mm
(6.30 inches)
Medium Medium Very Good
Small Wheel Hub/
200mm Tire
200mm
(7.87 inches)
Medium Medium Very Good
Large Wheel Hub/
250mm Tire
250mm
(9.84 inches)
Small Large Very Good
200mm Omni-directional
Wheels
200mm
(7.87 inches)
Medium Medium Good

VEX Plastic Wheels and Hubs

Most of the wheels for the VEX plastic construction system consist of a plastic hub and a rubber tread which is slipped around the hub. The 20mm Pulley is also used as a wheel hub. The 100mm Travel Rubber Tire which is paired with the pulley does not have as much traction as the other tires. The Rubber Tires are labeled with how far each will travel with one wheel rotation. Wheels are available in the Super Kit, the Competition Add-on Kit, the Wheel Base Pack, and the Wheel Add-on Kit. The following wheels can be assembled:

20mm Diameter Pulley &
100mm Travel Rubber Tire
Small Wheel Hub &
160mm Travel Rubber Tire
Small Wheel Hub &
200mm Travel Rubber Tire
Large Wheel Hub &
250 Travel Rubber Tire

200mm Omni-directional Wheels

The 200mm Omni-directional Wheels are special wheels which have a series of double-set rollers aligned around the circumference of the wheel. This feature allows the wheels to roll forward and backward, plus roll from side to side. Omni-directional wheels allow a robot to turn much easier than the rubber tires because of the rollers. 

Another advantage to using omni-directional wheels is that they allow for more advanced drivetrain designs which can move forward/backward and side to side. This is accomplished by using special orientations of the omni-directional wheels. When a drivetrain can move in this fashion, it is called omni-directional. Omni-directional wheels are available in the Competition Add-on Kit and in 2-packs.

200mm Omni-directional Wheels