Bare Motor Drivetrain
Direct-drive wheels on a motor pair. Covers shaft-to-wheel constraints, motor mounting, and dead-axle vs live-axle tradeoffs.
Before you start
Decide live-axle vs dead-axle. Live axleThe shaft spins with the wheel; bearings support the shaft, and the motor drives one end of the shaft. Simple, but the whole shaft length sees the wheel's load. is simpler; dead axleThe shaft doesn't move; the wheel rides on bearings around the shaft. The motor drives the wheel directly. Heavier but the shaft only sees side load, not torque. is stronger for hard-hit drivetrains.
1Pick the motor and gearbox ratio
FTC motors top out around 6000 RPM bare. Drive wheels target 200–400 RPM under load, so most direct-drives use a ~30:1 to ~13:1 gearbox already integrated into the motor. Pick yours before designing around it.
Free-speed RPM × wheel circumference = top free speed. If that's under 4 ft/s, the robot will feel sluggish; over 8 ft/s and it'll be hard to control.
2Lay out the wheel and motor positions
Sketch the drivetrain footprint on the top plane. Drop the motor outline (use the COTS library version, not a placeholder rectangle) and offset the wheel center by the motor's output shaft length.
Reserve packagingThe motor body sticks inboard from the side plate. Mark out a no-go zone around it now or your intake/lift will be designed into the motor's space. for the motor body inboard of the plate.
3Mount the motor to the side plate
Use the motor's mate connector to position it. Bolt pattern depends on the motor — most goBILDA motors use a 4-hole pattern on a Ø32mm circle.
The motor's output face should sit flush against the plate so the shaft is fully supported by the plate's hole and not just the motor's internal bearing.
4Couple the wheel to the shaft
If you're live-axle: hex shaft straight through the wheel, set screws or hex bore on the wheel hub to hold position. If you're dead-axle: bearings inside the wheel hub, motor output spins the hub directly via a coupler.
Set screw vs hex boreSet screws strip the shaft and slip under shock load. A true hex bore is the right answer for power transmission — set screws are fine for accessories like spacers but not for delivering torque. matters for reliability.
5Add the opposite side and cross-brace
Mirror the side plate, motors, and wheels for the other side. Cross-brace the chassis with structural extrusion or sheet members — the more triangulated, the less wheel toe-out under load.
Sanity check: with the assembly's Play view, the wheels should rotate when you drag a motor shaft; the chassis itself should not deform.
Bare motor drives are simpler than parallel-plate but harder to upgrade. You traded packaging flexibility for fewer parts — if that's your tradeoff, this is the right build.