Four Legged Walking Robot, uses 3-D pantograph arrangement to produce a gravitationally decoupled leg mechanism similar to that used by Shigeo Hirose, A Study of Design and Control of a Quadruped Walking Vehicle, The International Journal of Robotics Research, Vol 3, No. 2, 1984.
Won a Silver medal at the 1988 Model Engineer Exhibition.
Photograph - Scale Models International, April 1988, p207.
Design and building started September 1987.
Size - body about 6" * 6" * 6", leggs extend to about 15" * 15".
Operational area - 4ft * 2ft plus host computer.

I built First-Step in 1988 because I liked the look of the quadruped built by Hirose and Umetani and published in Robotics Research. However after building it I realised that using the 3d pantograph design to achieve a gravitationally decoupled leg mechanism was not the way to build legged robots. The legs are far too flimsy with too many parts and joints and for the design to work the body must be kept absolutely horizontal. Also work on First-Step came to a halt because it used small multiturn potentiometers for position feeback of the screw jacks, however the sample I used must have been very worn because when I obtained more and fitted them they consumed half the motor power and First-Step couldn't raise its body!

Text accompanying First-Step when on display at the International Model Engineering Show 1988 at Wembley, England. First-Step was awarded a Silver medal and contributed to my being awarded the Fantasy and Science Fiction Trophy for that year.
There wasn't a more suitable category in which to enter working robots so I had to compete with plastic kits etc. and the Gold Medal went to a modified plastic kit.

FIRST-STEP
This is not a model of anything. This is a real experimental walking robot built to explore the general problem of getting machines to walk and to cope with rough terrain (e.g. steps pot-holes etc.).

It is though, still unfinished lacking:-

• Motor drive electronics;
• Computer interface electronics;
• Sole sensor plates to detect when a foot is on the floor;
• Leg and foot sensor plates to detect contact with obstacles;
• Body pitch and roll sensors;
• Ground mapping sensors so the machine can place its feet with confidence.

When First-Step is finished as projected and barring unforeseen snags it will be Britain's only electric powered advanced walking robot. [Britain's only other 'walker' has six pneumatically powered legs.]

The position of each foot is controlled through a parallelogram leg mechanism by three screw jacks each driven by an electric motor.

The parallelogram mechanism allows movement along each of the three axes (forward/backward up/down in/out) to be independent of movement along the other axes and there is one jack for each axis. This arrangement produces a so called gravitationally decoupled leg mechanism wherein the actuators do not have to do work holding up the body but mearly overcome the frictional force in the bearings.

[The display base is not part of the robot but allows it to be posed to show the range of travel of the legs.]

D Buckley Dec. 1987