Drive motors

Brushed vs brushless

	Brushed gearmotor	Brushless gearmotor
Control	Any cheap brushed ESC	Needs a combat-tuned sensorless ESC (firmware); beetle-size sensored motors are rare
Low-speed control	Excellent, smooth from 0 rpm	Good with a proper firmware tune; can cog at a crawl
Power density	Lower	Higher — more power per gram
Electrical noise	High — can trip the weapon ESC (see below)	Low
Cost	Low	Moderate
Typical use	Budget builds, no-weapon control bots	Most current beetleweight drive

Brushed gearmotors still make a fine first drive — predictable and forgiving of the electronics. But purpose-built brushless combat gearmotors have become the norm at the competitive level for their power density.¹²

Common insect-class drive motors

Both brushed and brushless combat gearmotors are sold ready to bolt in, with combat-grade output shafts and mounts, by suppliers such as Just ’Cuz Robotics, Repeat Robotics, and Fingertech. Ian Talbert maintains a widely-shared comparison chart of the current beetleweight drive-motor options.²

• Brushed combat gearmotors — e.g. Just ’Cuz Viper / Dragon / Gecko, Repeat Compact Brushed. Integrated planetary gearbox, ~20:1 to ~100:1.
• Brushless combat gearmotors — a small outrunner geared down in a sealed housing. All brushless drive motors are outrunners (small inrunners spin far too fast) — protect nearby wiring from the spinning can.²
• Hub motors — brushless outrunner with the wheel on the bell. Compact, no gearbox, but limited torque and exposed.
• Generic AliExpress gearmotors — not recommended; if you must, use all-metal planetary gearboxes.²

Sizing

Work backwards from Power, torque & gearing:

1. Target top speed (3–6 m/s for a beetle) and wheel diameter (30–50 mm).
2. Required wheel rpm = speed / (π · d).
3. Pick motor Kv and battery voltage so Kv · V / gear_ratio gives that wheel rpm with ~15–20% headroom.
4. Check stall torque at the wheel exceeds the traction limit so the tires break loose before the motor stalls in a pushing match.

Team Run Amok’s calculator models steps 1–4 for common combat motors.³

Thermal and duty

Drive motors in a pushing match run near stall — high current, low rpm, poor cooling. Mitigations: gear so the tires slip before stall, use 4 motors to share load, allow cool-down between matches, and pick motors with generous continuous ratings. Melted brushed motor magnets and desoldered brushless windings are common failure modes.

Redundancy

4WD (four motors) keeps the robot mobile after losing a motor or wheel to a hit, and adds pushing traction. The cost is mass and two more ESC channels. Most competitive beetles are 4WD.

Brushed motor noise

High-power brushed motors put electrical noise on their leads that can induce false signals in the receiver or weapon ESC — the classic symptom is the weapon twitching or a servo jumping when you drive. Fixes, roughly in order: route drive leads away from the receiver and weapon wiring; twist the motor leads and signal leads; solder 0.1 µF non-polarised ceramic capacitors across the motor terminals (and from each terminal to the can for more suppression). A capacitor on the weapon ESC’s signal pads is a last resort — it also blocks the programming signal.²

References

Footnotes

1. Meggiolaro, M. A. RioBotz Combat Robot Tutorial, v2.0, PUC-Rio, 2009 (CC BY-NC-ND) — DC motor selection, gearing, and thermal limits. ↩

2. Ping, L., with L. Skotiniotis, I. Talbert & D. Tran. Beetleweights for Dummies (Fall 2025 revision) — builder-maintained beginner guide distributed via the NHRL Discord. Sections: Drive Systems; Brushed Motors & ESCs; Brushless Motors; Appendix IV (Brushed Motor Noise). ↩ ↩² ↩³ ↩⁴ ↩⁵

3. Team Run Amok — Tentacle Torque & Amp-Hour Calculator and the “Ask Aaron” motor archives. ↩