Project : Develop an obstacle avoidance system for a simple mobile robot

The Construction Automation and Robotics Labororatory at Texas A&M University was investigating the possibility of using "Clod buster" derived vehicles as mobile robots. Hobbiests have developed a number of improvements to the basic vehicle. A 6-wheeled aluminum chassis was used for this project. Two ultrasonic transmitter-receiver pairs were mounted on the front and one was mounted on the rear. The schematic of the transmitter circuitry is here. After initial testing it was determined that focusing devices were needed for the ultrasonics. Paper cones were used, giving the vehicle the appearance of having horns and a tail.

A single board computer (SBC) based on the Motorola M68HC11 was used to control the triggering of the ultrasonic sensors and generate the pulse width modulation (PWM) signals necessary to drive the steering servo and electronic speed controller used by the vehicle. A fuzzy logic system was used to determine the steering and speed signals.

The ultrasonic sensors generated a signal that triggered an interrupt on the SBC. To maintain the integrity of the PWM signals being generated the interrupts were disabled during PWM signal generation. This meant that obstacles in the immediate vicinity of the vehicle were not detected.

A typical fuzzy input set consisted of the regions: Very near, near, medium, and far.

For additional details see

Scott, W., Berrios, I, and Boles, W., "An Educational Mobile Robot," Microcomputers in Civil Engineering, Vol. 10 No. 3 pp. 243 - 249, May 1995. Abstract

The original Mechatronics class project report (56 pages, 159 kBytes) The full assembly language source code is included.