Mario's Lego Robotics Archive

SHRIMP II

This is my second version of SHRIMP, a high mobility wheeled rover designed by the Autonomous Systems Lab based in Lausanne, Switzerland.

The major difference of SHRIMP II against my first version is its ability to turn.

The vehicle is fully described in my book Building Robots with LEGO® Mindstorms™ and I provide here in this page just some pictures and a short list of its main features:

  • The front and rear wheel assemblies mount the motor very low, just over the gearbox.
  • There's a long (joined) axle that crosses all the body of the robot and operates the front and rear steering together (they obviously turn opposite). A motor controls the steering.
  • The RCX has three ports connected: 1 out for the power, 1 out for the steer, 1 in for the touch sensor that detects the central position of the steer.
  • For the robot to turn properly, the inner side wheels must be stopped as in a skid-steer drive. This is achieved using two polarity switches operated by the rear steering assembly. A rubber keeps them gently pulled in ON position. The rear wheel pivoting axle as a traverse axle attached to its top, that during turn pushes also one of the switches. Approaching about 45° in steering angle, the switch goes off and the connected wheels stop.
  • It turns well enough. During very large turns all the motors are on but they can make with the difference in speed. In tighter turns, the inner wheels stop and the SHRIMP turns around the midpoint of its inner side wheels group.
  • It's a bit less robust than my first version. I wouldn't suggest to make it turn while facing complex and articulated obstacles.
  • The front wheel has shorter arms to the body (12 instead 16 studs beams) to compensate with the size of the steering system. This reduces a bit the maximum height it can climb.
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