Lego Mindstorms NXT


Beta Bob

This is Beta Bob (Alpha Rex’s cousin aka PatrolBot), my best attempt at a biped so far. The legs are pretty much those from Omni-Biped in ’Creating Cool Mindstorms NXT Robots’ by Daniele Benedettelli. These are the best biped legs I have found: simple, smooth, able to reverse and turn, and most of all stable.

Each leg is powered by one motor and the third motor rotates the torso, raises and lowers the left probe arm and the head.

 A touch sensor is mounted at the rear and is used to initially align the legs and torso thus eliminating the need to manually set the robot up before it will work.

The sonar sensor is mounted in the head and used to detect large obstacles. A light sensor forms the right hand. This is not used as a sensor but as a light source for Beta Bob’s ’laser’ gun. A colour sensor (or another light sensor) forms the left hand and is used as a probe to detect small objects (e.g. legs of chairs or giant alien spiders) that the sonar can’t see.

 When Beta Bob is activated, firstly the legs are aligned in the correct position and the torso is centred. Beta Bob then starts walking forward, all the time scanning left and right and up and down for obstacles and targets. If a large obstacle is detected by the sonar he stops, backs up a bit and then turns left or right a random amount. He then starts walking forward again. If his ’probe’ detects a target, he stops, backs up a little and then destroys the target with his ’laser’. He then turns and continues to patrol.

 Quite a lot of the parts are just used to make Beta Bob look better. Most of these come from the Power Functions Bulldozer set and don’t affect the operation so can be left off or changed.

 Beta Bob works really well. The one weak spot is the crown wheel that drives the torso. This has a tendency to jump a tooth occasionally. If the torso gets too far out of line the probe arm can start to hit the body which tends to be a bad idea.

Front Left Back Right
Front view with all the embellishments removed.

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