Drive Systems
A robot's drive system – its motors, gearing and wheels – decides how fast it goes, how hard it pushes, and how well it handles. A great weapon is useless if the robot can't get it to the opponent. This page covers drivetrain layouts, motors for each weight class, gearing, and protecting the drive from hits. See also Wheels, Motors and Insect Class Motors.
Steering
Almost every combat robot uses tank steering (also called skid or differential steering): the wheels on each side are driven separately, and the robot turns by running the two sides at different speeds. It's simple, strong, and lets the robot spin in place. Car-style steering isn't used. Your radio mixes throttle and steering for you (see Radios/Mixing). For other steering types, see NameThatPart.
Layouts
- 2-wheel drive (2WD): light and simple, and favored by many top robots, but the wheels need to carry most of the weight (around two thirds) or they lose traction, and the robot can tip under hard acceleration.[1] Many drum spinners use 2WD.
- 4-wheel drive (4WD): pushes harder and tracks straighter, but drags its wheels sideways when turning. Small robots often drive four wheels with two motors, using belts or gears to link the front and back wheels on each side.
- 6-wheel drive: usually with the middle wheels set slightly lower so the robot pivots on them when it turns.
- Mecanum and omni wheels let a robot drive sideways, but give up traction and pushing power, so they're rare in combat.[2]
- Walkers and shufflers get weight bonuses under SPARC rules: 1.25× for shufflers, 1.5× for non-traditional drives (such as vibration or bristle drives and hovercraft), and 2× for true walkers (see SPARC Robot Construction Specifications).
Transmitting power
- Gearmotors – a motor with a built-in gearbox driving the wheel directly. The most common choice in insect classes.
- Belts – link wheels on the same side, and can slip a little under shock, protecting the gearbox.[3]
- Gears and chains – strong and no slip, but they pass every shock straight to the motor. Chains are mostly seen in larger robots.
- Friction (tangent) drive – a brushless motor's knurled shaft presses directly on the tire, with no gearbox. Light and simple, but it needs firm tires and the right amount of pressure: too little slips, too much overloads the motor.[4][5]
Motors by weight class
Typical choices as of 2026. Products come and go, so check the Suppliers.
- 150 g: N20 and smaller N10 brushed micro gearmotors, such as FingerTech Mini Sparks and Pololu micro metal gearmotors.
- 1 lb: N20s, 16 mm brushed gearmotors such as the FingerTech Silver Spark and Repeat Mini Brushed, and small brushless gearmotors.
- 3 lb: 22 mm brushed planetary gearmotors (FingerTech, Repeat Robotics, BotKits), or brushless gearmotors such as the Repeat Compact and FingerTech Brushless Mega Spark, and Just Cuz Robotics Blitz motors.
- 12 lb and 30 lb: larger brushless gearmotors, often with hex output shafts, such as the Repeat Ultra and Magnum, and Just Cuz ZomBox.
- As a rough guide for brushless drives, all the drive motors together usually weigh around 2–3% of the robot's weight. Brushless drive performance depends heavily on the ESC and its firmware (see ESCs).[6]
Gearing and speed
Top speed (with no load) is:
- Speed = π × wheel diameter × (motor RPM ÷ gear ratio)
For brushless motors, motor RPM is roughly Kv × battery voltage.
Examples:
- A brushless gearmotor with a 2300 Kv motor on a 3S battery (11.1 V) spins about 25,500 RPM. Through a 22.6:1 gearbox that's about 1,130 RPM at the wheel. With 1.75" wheels: π × 1.75" × 1,130 ≈ 6,200 inches per minute, or about 5.9 mph.
- An N20 gearmotor turning 1,215 RPM with 1.25" wheels gives about 4.5 mph. Around 4 mph is plenty for an antweight in a small arena.[7]
Real robots go slower than these no-load numbers. Faster isn't always better: lower gearing gives more acceleration and pushing power, which matters in small arenas, and extra power beyond what the tires can grip just spins the wheels. Team Run Amok's optimum gearing guide and the Tentacle torque calculator (brushless version) help you choose. See also Speed Reduction and OnlineTools.
Protecting the drive
- Support the output shaft. Don't let the wheel hang off the end of a gearmotor's shaft; support it on both sides with a bearing where you can.[8]
- Mount motors mechanically with proper clamps or mounts – not glue, tape or zip ties.[9]
- Harden your gearboxes: threadlock the screws, and glue gearbox cases that tend to come apart. See Hardening Motors.
- Shock-mount the drive or the whole chassis in high-energy classes (see Armor and Materials).
- Keep the wheels covered by wedges or armor where possible (see Wheels).