Tiny metallic DC motor
N20. 80RPM and 0.5 kgcm at 6V. D-shaped shaft, suits our white 43mm wheels.
The speed of brushed DC motors is approximately proportional to the voltage you put on them. Double the voltage can give you double the speed, but beware of issues such as torque limitations, overheating and faster wear.
Price: $6.00 AUD (for each Tiny metallic DC motor)