Problem controlling DC motors

I have build a autonomous vehicle with arduino. But I don't what the measurement of the motors really means, it says from 0-255. But does it mean velocity, rpm...
Could someone explain it to me?


It means the Arduino is putting OUT Pulse Width Modulated power, over a range from Zero to Maximum. 0..255

It knows NOTHING about what you have connected to it.

You have to characterize Your motors, motor driver and motor power supply to find out how your motors will react to the different PWM signal.

The same Arduino PWM signal can run different motors differently.