Dual dc-motor-speed controllers navigate robots

Shyam Sunder Tiwari, Robotics Software Pvt Ltd, Gwalior, India -- EDN, 3/29/2001

Mobile robots need simple and lightweight dc-motor-speed-control hardware that can work with low-power batteries. Flip-flop type navigation systems allow only one motor to operate at a time while the other motor remains off. Navigation direction changes alternatively even when the robot has to navigate through a straight path. Line-tracker robots are of this type.

Zigzag motion lets the robot look at the track toward its left and right such that it can correct its path if necessary. You can drive both motors if this type of motion is undesirable. The circuit in Figure 1 has two independent motor-speed-control channels: one for a righthand-side motor and the other for a left-hand-side motor. Power to each motor is pulse-width-modulated using a Basic computer program (Listing 1). The power-driver circuit uses npn power transistors, Q₁ and Q₂. These transistors have high-power-kicking ability that the robotics require. The PC's parallel port directly controls the base of these transistors. LPT port data bit D₀ operates a righthand-side motor, and data bit D₄ operates a lefthand-side motor. Level one at the port pin turns on the motor power, and level zero turns off the motor power. If both D₀ and D₄ are set to one, then both motors operate together. Reverse control does not occur. Thus, only one motor needs to operate to turn the robot backward until rotation is complete. You can add feedback sensors to the hardware. These sensors are necessary to know the position of the robot. The circuit works for small dc motors operating from a power source in the range of 3 to 12V.