Mario's Lego Robotics Archive


A walking bot. It has a very limited behaviour: cannot change direction, cannot detect obstacles, it simply walks. But it walks with just two legs, which implies it has to move its centre of gravity to keep it inside the base of the single leg that is touching the ground.

I got this by moving the heaviest thing that's on the bot: the RCX. It is mounted on a motor driven slide that can move right and left.


- Both legs touching the ground and still. RCX starts to move itself left. When it's in proper position over left leg, it stops.
- Right leg is moved up, forward and down until it touches the ground again, then it stops.
- Now RCX starts sliding right until it's over the right leg.
- Its left leg turn to move up, forward and down until it touches the ground. Then the cycle ends and starts again.

I used one touch sensor to detect the slide position, one Hall-effect sensor to know when both legs are touching ground, and another touch sensor as a trigger to get S6 stopped in proper phase. The homebrew Hall-effect sensor may be easily replaced with a standard Lego touch sensor.

Raising the right leg...

...and then the left one (yes, seems to fall, but it doesn't).

Right side view.

Top view (RCX removed).

Detail of the Hall-effect switch and the permanent magnets. For each step the large pulley rotates 180 degrees.

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