Boadicea - Leg Design

Leg design is critical for determining a robot's mobility. Boadicea's legs were designed to address problems that hampered previous robots.

The advantages of Boadicea's leg design are:

• a large workspace
• linear foot motions
• a relatively small and compact mechanism
• lightweight construction

The design of Boadicea's legs was inspired by studies of real insects. The legs use a pantograph mechanism to produce a large workspace with linear foot motions.

Insect inspirations

Boadicea's legs are modeled after the cockroach Blaberus Discoidalis (See picture below), and differ from previous designs in two important ways:

• Large, overlapping workspaces
• Different front, middle, and rear legs

Leg Workspaces Boadicea's legs have long, overlapping workspaces, allowing the robot to maintain stability when one leg is damaged. Long workspaces also increase speed by extending the stride length. This picture shows the workspace of the cockroach on the left and Boadicea's workspace on the right.

Workspace of Blaberus Discoidalis and Boadicea

Optimized Leg Designs

Like an insect, Boadicea has different front, middle, and rear legs. Optimizing each leg design for the role it plays in locomotion improves the robot's performance.

Pantograph mechanism Boadicea's legs use a 2 dimensional pantograph mechanism. Several walking robots incorporate this mechanism because it produces linear foot motions, simplifying software requirements [Hirose 84].

A second advantage of the pantograph is that it provides a large leg workspace with a relatively simple and compact mechanism. Boadicea's legs have a greater range of motion than other walking robots. Attila, Genghis, the Adaptive Suspension Vehicle, the OSU Hexapod, and other robots have all had a maximum step length about one third of the total body length [Angle 89] [Angle 91] [Waldron, et al 84] [McGhee and Iswandhi 79]. Boadicea's rear legs have a maximum step length nearly 70% of the total body length.

Because Boadicea is a much smaller and lighter robot, the pantographs can be much simpler than that used on other robots. Boadicea's pantographs are made from injection molded plastic, and use low-friction sliding prismatic joints. Pantographs on other robots must support large loads, requiring metal construction and complex bearing components [Waldron, et al 84].

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