Turn the robot with the mouse or your finger. Click an axis (a coloured circle or a card) to light up its ring and its axis and to read its description, press X-ray to look inside at the motors, gearboxes, controller and cables, and move each joint with its slider.
It rolls forward only and cannot slide sideways. The simplest and most common wheel: the wheels of a differential-drive robot. This slider sets the rolling speed of all the wheels.
A small free wheel behind a vertical pivot: it swivels by itself and trails behind. It has no motor and only supports the robot. The slider swivels it.
A driven wheel that a second motor turns about a vertical axis: it can point anywhere (swerve drive; cars use the same idea). The slider steers it.
Small free rollers around the rim, in line with the rotation: the wheel drives forward and slides sideways freely. Used on holonomic bases with 3 or 4 wheels.
Rollers at 45° around the rim: with four such wheels the robot moves in any direction by combining the wheel speeds. It needs a flat floor and a suspension.
A ball driven by three rollers: it rolls in any direction, so a robot can even balance on it (ballbot). Complex and costly.
A belt around sprockets: large contact area, good on soft or rough ground, turns by skidding. Used on rovers for sand, snow, mud or stairs.
The seven wheel types stand in a row at the same scale. The first slider sets the rolling speed of all the wheels (and of the track), the second swivels the castor, the third steers the driven wheel. The model is simplified: see the lab above on the wheels page to watch how each wheel behaves when pushed.