This was the proof-of-concept working model of the leg modules for Pentagoon. We went on to build 5 final-version legs.

Computer-generated pictures and photographs:

The computer-generated picture (left) and the real version (right) of the whole leg.

The computer-generated picture (left) and the real version (right) of the hip unit.

The computer-generated picture (left) and the real version (right) of the powered wheel on the bottom of the leg.

Mechanical details:
The leg uses two servomotors, one of which (powering the wheel) has been modified for continuous rotation. The telescoping mechanism ("hip") is built on a piece of blank unetched printed circuit board; it consists of two nesting square-section brass tubes (about 5mm diameter or so), the outer of which is soldered to the board and is moved by the servo using a lever and connecting rod to give about 5cm of travel. In fact the connecting rod does not move the inner tube directly; it moves a small piece of the larger size of the tubing that sits on the top end of the leg, with a slot in it through which a peg from the inner tube protrudes. When the inner leg is touching a solid surface, the peg rest at the top of the slot, closing a microstich mounted there; if the leg loses contact with the ground (either on purpose, by the leg being lifted up, or through the robot driving off the edge of a higher platform) the microswitch is opened and the robot can take appropriate action.

The wheel is a disc of perspex bolted to a servo horn on the output shaft of the lower motor. On either side of the motor (not shown in the 3d model) are microswitch bumpers, to detect collisions; the tag of metal sticking straight out will hold a photoreflective IR sensor to read an encoded on the wheel for odometry purposes in the finished robot.