Control of position/velocity in a mobile robot using DC brushless motors

This paper describes the construction of a differential mobile robot using a brushless DC motor coupled to each wheel. Considering that commercial controllers of brushless motors are expensive and they control only velocity, not position; we design and built 3-Phase Bridges, with N-Mosfets, within a electronic circuitry to drive brushless motors. A PWM control scheme and the outputs of the optical encoder and Hall sensor of the motor are used to implement a closed-loop velocity and position control. The real time control of the two traction wheels runs on a 68HCS12 microcontroller and the mobile robot accepts commands using an standard RS232 serial connection. The hardware design and software of this robot is available online.