This buggy will turn about 120 degrees anticlockwise whenever it detects an obstsacle in front of it. An Ultrasonic Astable Blok with a transducer attached generates the sound wave. When the receiver detects a large enough reflected signal, it triggers a relay which reverses one of the motors for a second or two, causing the buggy to rotate and change direction.
The ulrasonics need to be mounted parallel to each other facing forwards.
To reduce sensitivity, detune the astable slightly so it runs slightly off its optimum frequency.
The motors and gearboxes are meant to be exactly the same in the video you can see the buggy veering to the left instead of straight..
An ultrasonic wave is continuously transmitted in front of the buggy. When a signal is reflected back from an obstable, one buggy motor reverses. Apologies for the photo, I couldn't find a better one.
The length of time the motor reverses for, can be adjusted using VR1 on the monostable.
Use 40KHz transducers for the U/S TX and RX.
Circuit Voltage: 6 to 9 volts
Motor Supply: as required