Mechanical / physical

The motors spin but the robot doesn’t drive

Wheels are slipping on the axle or the chassis is sitting on cardboard instead of the tyres.

The problem

You can see the motor shafts turning. The vehicle stays put, or one side drags.

1
Look from the side. If cardboard edges touch the table, trim them so only the wheels bear weight. QA chassis often sat on a flap after gluing.
2
Push the wheel onto the shaft until it cannot spin independently. Tape or a cardboard bushing helps if the hole is oversized.
3
If only one motor turns, that side’s pin, driver, or wire is open. Swap the two motor connectors. If the fault follows the connector, the wiring is wrong. If it stays on the same motor, the motor is the fault.
4
Do not press down on the vehicle to “help” it. That stalls the motors. See the safety note on hot motors.

If you walked the steps and the mechanism still does not move, write to us. This is the fallback, not the first stop.