Wheels, Tread, and Motors

Wheels and tread#

The wheel's grip is set by its coefficient of friction (CoF) against the carpet. Common FRC choices:

• Colson Performance Wheels — solid polyurethane wheels that are durable and reasonably grippy with a long lifespan. A frequent default. Carpet nap can introduce a small amount of odometry error, so teams that rely on wheel-based odometry usually still fuse it with a gyro and/or vision.
• Treaded traction wheels (e.g., WCP/VEXpro Plaction-style wheels wrapped in blue nitrile roughtop tread) — very high grip; AndyMark lists blue nitrile roughtop at a CoF around 1.19 on tight-pile carpet. The trade-off is that the tread wears and must be replaced periodically.
• Omni wheels — rollers around the rim let the wheel roll sideways freely; used at the corners or center of tank drives to ease turning.

A common WCD setup mixes high-grip traction wheels with omnis, or uses all traction wheels with a center drop.

Motors#

FRC motors you will see on drivetrains and mechanisms (specs from REV's published comparison):

• CIM — the classic brushed workhorse; large diameter (2.5"), lots of legacy hardware built around it.
• NEO (REV) V1.1 — brushless, free speed ~5,820 rpm, stall torque ~3.0 N·m, stall current ~160 A.
• NEO Vortex (REV) — brushless, free speed ~6,784 rpm, stall torque ~3.6 N·m, stall current ~211 A.
• Kraken X60 (WCP/CTR Electronics) — free speed ~6,271 rpm, stall torque ~4.21 N·m, stall current ~233 A.
• Falcon 500 V2 — free speed ~6,489 rpm, stall torque ~3.46 N·m, stall current ~191 A.

Current limits and brownouts#

The stall-current numbers above are why you must set motor current limits in software (the smart motor controllers — Talon FX, SPARK MAX/Flex — do this). Pulling stall current on several motors at once can sag the 12 V battery and brown out the roboRIO, which cuts motor outputs mid-match. Limiting drive current (commonly in the 40–80 A per-motor range, tuned per design) protects the battery and the motors and keeps the robot above the brownout threshold.

Choosing#

For a drivetrain, pick wheels grippy enough that you are not pushed around, geared so the robot is fast enough but cannot easily stall (see the gear-ratio lesson). Match motor count to robot weight: heavier or defense-oriented robots want more motors and more grip.