Wheelbases are anything that is used to get around. They consist of a frame, and some number of wheels (almost always 4, but you can have a different number).
There are 3 main types of wheels in VEX. From left to right, they are: mecanum wheels, omnidirectional wheels, and high traction wheels (the right two).
Each wheel has different uses in bases, and should be used differently, generally with a different frame.
I’ll start with high traction wheels, which are the easiest to use in wheelbases. The frame is simple, just a square with two wheels on opposite sides, like so:
You can power the wheels on the same sides with one motor, as they always need to go in the same direction. To turn, the wheels on opposite sides need to go in opposite directions. Note that there are 4 different sizes of high-traction wheels.
The next easiest base uses omni-directional wheels, and although they can be used in the above base, they are better used in what is known as a holonomic drive, which takes two forms:
In both cases, each motor is powered independently. This wheelbase has a 360° range of motion, regardless of orientation. However, it tends to move slower than the traction wheelbase, being more specialized in turning.
The most confusing type of wheelbase uses mecanum wheels. It looks like the traction wheelbase, but each wheel is powered independently. The top rollers of the mecanum wheels have to form an “X” shape to work properly. In this orientation, moving the wheels opposite to each other diagonally in the same direction while the other diagonal move in the opposite direction causes the wheelbase to move sideways, rather than flail around aimlessly.
This gives the wheelbase full freedom of movement, with an emphasis on moving forwards rather than any other direction. However, mecanum wheels tend to give odd results with encoders (more on encoders in the sensors section).