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28 August 2010

Timbug-II - built by David Buckley March 1992
Timbug-II - HM
Maybe the first published design for a robot vehicle using ultrasonics for obstacle detection. Uses an ultra-sonic beam to detect obstacles, avoidance is by random back-off and turn behaviour.
Based on a design published in Elektor, June 1980.
Built March 1992.
Size - 5" * 3 1/2" * 3".
Operational area - 3ft * 3ft.
There were no photographs in the Elektor article so I built Timbug-II in the style of other projects in Elektor using acrylic sheet and pcb spacers. The motors are from a motorised Tank kit obtained in a box of bits from the flea market at the end of Portobello Rd sometime in the late 70s. Timbug-II's speed is not high but since the wheels are about twice the diameter of the track drive sprockets it is about twice as fast as the tank would have been. The circuit worked but the movement times were far too long for Timbug-II as built and I had to reduce all the time constants by about a factor of ten.


  • The Ultrasonic sensor picks up mechanical noise from the gearboxes and really needs a soft mounting rather than being epoxied in place.
  • The Ultrasonics only see a wall if it is within 10deg. of the Normal.
  • The Ultrasonics won't see a wall if it is closer than about 2 inches because there is not enough of the beam reflected into the receiver.
  • Hence if the robot is heading to a wall and sees it then it will backup and turn but then the wall will be too far off from the Normal to reflect the beam back to the receiver and so the robot crashes into the wall.
  • The beam isn't powerfull enough to detect most objects.

    Elektor, June 1980

    Plan and Circuit of my version

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