Wheel

Wheels are fundamental components for robot motion and are used more often than any other method of locomotion (such as treads).

Types

Various types of wheels exist, including standard, grip, holonomic, and mecanum.

Standard

Standard wheels are the ones which ship with the FIRST kit of parts. Originally 8 inches in diameter, the size was changed to 6 inches for the 2007 season.

Grip

Grip wheels are generally mde from aluminum disks sandwiching an aluminum roller which is coated with a high-friction tape material. They offer much more traction than a standard wheel and are often custom-made or order from specialty suppliers.

Holonomic

Holonomic wheels have small, free-spinning disks oriented perpendicular to the rotating direction of the wheel. This allows the wheel to slide sideways with a minimum of friction and is useful in many hybrid variants of the swerve drive and castor drive. Holonomic wheels are typically rather expensive and generally ordered from specialty suppliers rather than fabricated by teams themselves.

Mecanum

Slightly similar to holonomic wheels, mecanum wheels also incorporate free-spinning rollers, but oriented at 45-degree angles to the direction of wheel rotation. When the rollers on sets of opposing wheels are aligned in opposite directions, reversing the direction of one of the opposed wheels enables the robot to move sideways. These are typically used in complicated variants of the swerve drive system, when design requirements dictate that there is not enough space, weight capacity, etc. for a more conventional swerve drive. The mathematical/kinematics model for mecanum wheels is quite complicated, and the wheels themselves are usually exceedingly expensive and complex; a set of four often approaches the $400 maximum for any single robot part.