If you are not familiar with Mecanum wheels, this 48mm diameter Mecanum wheel might look like an ordinary wheel made with mini hair rollers. In reality, it is a very clever omnidirectional wheel with rollers supported by ball bearings, allowing a four-wheeled robot to move in any direction. It has nine rubber beads around the perimeter that allow it to grip the floor when moving laterally.
These wheels have a small insert that allows them to be used with LEGO-compatible cross-axle motors or inexpensive TT motors. They simply snap into place.
This is the LEFT wheel; you will recognize it because it has an L engraved on the hub. You will need at least 2 left wheels and 2 right wheels to use all movement combinations.
