Mecanum and Other Omnidirectional Drives

Mecanum wheels#

A mecanum wheel has angled rollers (typically 45 degrees) mounted around its circumference. When the four wheels spin in the right combination, the angled rollers create force vectors that let the robot translate forward, sideways, and diagonally, and rotate in place. Unlike swerve, the wheels stay fixed; only the motor directions change, so there is no steering motor.

How motion works#

• All four forward → drive forward
• Left pair forward, right pair backward → spin
• Front-left and rear-right forward, others backward → strafe sideways

The rollers contact the ground at an angle, so a mecanum wheel exerts relatively low ground friction in the direction it needs to slide. That is exactly why it can strafe, but it is also its weakness.

Trade-offs versus swerve and tank#

• Pro: omnidirectional like swerve, but much simpler (four motors, no steering, no per-module encoders).
• Con: poor traction and pushing power. The angled rollers mean a mecanum robot is easily pushed around by defenders and loses traction on debris or ramps.
• Con: sensitive to weight distribution. If one corner is light, that wheel slips and the robot drifts off its intended path, so even strafing requires careful balancing or closed-loop correction.

Where it fits#

Mecanum is a reasonable choice for games with a flat, clean field and little expected defense, or for teams who want omnidirectional motion without the cost and software burden of swerve. AndyMark and other vendors sell COTS mecanum wheels. In modern, defense-heavy FRC games, however, most competitive teams choose either a grippy tank drive or swerve, and mecanum has become uncommon at the top level.

Other variants#

• Omni-wheel "H-drive": a tank base with an extra perpendicular omni wheel (or two) in the center to add strafing. Simpler than mecanum but with limited side force.
• Octocanum/butterfly: a hybrid that pneumatically switches between traction wheels (for pushing) and mecanum/omni wheels (for strafing), giving you both modes at the cost of pneumatics and complexity.