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IntroductionHexotica - The Design and Implementation of a Small Walking Robot
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Introduction
Robotics is a rapidly expanding field of study. As robots become more sophisticated, new applications are being found for which they can be used. Improvements in controller power and robot design have allowed robots to be used in a number of different industries including nuclear power, forestry, defense, automotive and others.
Traditionally, most mobile robots have been equipped with wheels. The wheel is easy to control and direct. It provides a stable base on which a robot can maneuver and is easy to build. One of the major drawbacks of the wheel, however, is the limitation it imposes on the terrain that can be successfully navigated. A wheel requires a relatively flat surface on which to operate. For many applications this is acceptable, especially in very controlled environments. However, in other instances the environment cannot be controlled or predicted and a robot must be able to adapt to its surroundings. Rocky or hilly terrain, which might be found in such applications as forestry, waste clean-up and planetary exploration, imposes high demands on a robot and precludes the use of wheels. Research into legged robotics promises to overcome these difficulties.
The complexity of control required for a legged robot to navigate autonomously over unfamiliar terrain has made them difficult to build. Recent developments in embedded controller technology have yielded very sophisticated computing devices in relatively small, easily programmed modules. With these advanced components, it is now possible to control relatively complex and sophisticated devices.
The objective of this project is to design a small, robust walking robot with a unique control paradigm. The design uses a combination of control philosophies; using the inverse kinematics control method from industrial robotic arms combined with high level subsumption-like [1] architecture to guide the leg movements. This will give the robot a degree of control and range of movement unmatched with other small walking robots, while maintaining the same robust and adaptable behaviour. Low level control algorithms for the legs based on industrial robotic control allow the foot to be moved in a straight line path between any two points in the leg’s work envelope (an ability most walking robots of this size do not have). High level behavioural-based programs define these vectors, adapted according to the desired direction of travel and obstacles encountered along the way. The hardware and software design is highly modular, allowing for easy extension and adaptation of the robot systems. This robot provides a platform for the study of the control of legged vehicles, environment sensing, path planning and task accomplishment.
There are three distinct components to the project. The first is the mechanical design of the robot itself. Choosing a good mechanical design will facilitate all future work and will minimize the need for redesign. A good leg design will allow for simple and adaptive control of the robot’s motion.
The second aspect of the project is the embedded controller and the design of the electronic interfaces. It is very important to have a good interface between the controller and the components to be controlled.
The third factor involved in the design of the robot is the control architecture. The control scheme will rely on the mechanical design and controller chosen but this should only be at a low level in the control hierarchy. The actual software architecture should be essentially platform independent and should allow for the desired level of autonomy.
1.1 Motivation
The team members’ common interest in robotics was the leading factor in deciding the topic of research. During discussions leading up to the 3B workshop class, it was decided that an attempt would be made to expand upon the body of knowledge that applies to autonomous mobile robotics. Very often in engineering programs, students obtain a good background in the theory behind engineering practice, but do not get very much practical experience. By designing and building an autonomous vehicle for the Systems Design Workshop, the team members hoped to gain the practical experience required for further study in the robotics field.
The body of knowledge that applies to mobile wheeled robots is quite well developed. However, autonomous walking vehicles are still relatively new, and the body of knowledge concerning their development is not as well defined. The difficulty factor in building a legged robot is also considerably higher than that for a wheeled robot. The idea of building a walking vehicle began with an e-mail message from Mark Tilden, a University of Waterloo alumni now working at Los Alamos National Laboratories in New Mexico. In order to gain experience and insight into the development of walking vehicles, he suggested building a small scale robotic device which can then be used as a development platform. Creating such a platform is the fundamental purpose behind the project. Each component is designed using a modular design principle. This means that each part of the robot, such as a leg, is designed to attach to the rest of the system through a common interface that does not depend on any one design of the particular component. That way, a design change in one component does not necessitate changing any of the other modules.
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page. Last updated: April 20th,
1997