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Mechanical, Build & Pneumatics·Lesson 8 of 47

Wheels, Tread, and Motors

The contact patch and the motor define how fast, how grippy, and how strong your drivetrain is.

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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.

Key takeaways

  • Colson wheels are durable all-rounders; blue nitrile treaded wheels offer very high grip (CoF ~1.19) but wear out
  • Modern brushless motors (NEO, NEO Vortex, Kraken X60, Falcon 500) spin ~5,800–6,800 rpm with high stall current
  • Set software current limits to avoid sagging the battery and browning out the roboRIO

Go deeper

Lesson quiz

Required

Answer all 3 questions correctly to complete this lesson.

1.Why are omni wheels often paired with traction wheels on an FRC drivetrain?

2.What is true about the Colson Performa wheels widely used in FRC drivetrains?

3.Which of these motors commonly used on FRC drivetrains is a BRUSHED motor rather than a brushless one?

Answer every question to submit.