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 EXP Wheels
The diameter of a wheel 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 |
200mm (7.87 inches) |
Medium | Medium | Good |
|
5x Pitch Diameter Balloon Tire |
200mm |
Medium | Medium | Very Good |
| 2x Wide 3.5 Pitch Diameter Balloon Tire (Trapezoid Offroad Tread) |
140mm (5.5in) |
Medium | Medium | Very Good |
VEX EXP Wheels and Hubs
VEX EXP Kits come with 1.75 in Balloon Tire, 2.75 in Balloon Tire, 3.25 in Omni-Directional Wheel (see below for more information), and 3.25 in Anti-Static Wheel. Some of these, like the Balloon Tires, consist of a wheel and hub that must be fitted together.
| 1.75 in Balloon Tire | 2.75 in Balloon Tire | 3.25 in Omni-Directional Wheel | 3.25 in Anti-Static Wheel |
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200mm Omni-directional Wheels
| 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.