Spike: a novel cube-based robotic platform

Coyte, Christopher Keith
Collins, John
Beckerleg, Mark
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Master of Engineering
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Auckland University of Technology

This thesis documents the successful development of a novel form of robotic motion, inspired partially from bio-mimicry and partially from a search for unknown forms of legged robotic motion. The novel motion developed from the research in this thesis, was created by implementing a tilting and falling action on the robot as a result of its leg movements to form a unique robotic gait. The tumbling gait was developed on a six legged robot that featured a tri-pedal stance, with the robot driving its legs in such a way as to unbalance the robot and force it to fall onto an opposing leg, creating a tumbling motion. To create the desired tumbling motion, several robotic concepts were investigated. The final robotic version used a series of leg actuations that induced a tumbling action on the robot. This was achieved by moving one of the three grounded legs towards the centre of the robot, causing the robot to tumble in that direction, giving a triangular footprint to the motion. After determining the method most suitable for motion and reviewing the current literature in this field, the robotic chassis design was created based around the manufacturing abilities of a plastics three dimensional (3D) rapid-prototyping printer. This design was cube-shaped with a single leg protruding from each face of the cube, giving a total of six legs. This cube design included three axes of symmetry, featuring a collinear pair of legs mounted on each of the robot’s axes. The cube design incorporated leg mounting, electronic board mounts, battery compartments and internal strengthening. Due to the complexity of the design and the high level of integration between the electronics and mechanics, ‘off-the-shelf’ components could not be used, and a complete electronics design was created, prototyped and built, comprising multiple circuit boards for the required power, processors and input-output devices. Considerable electronic development permitted a wireless controlled semi-autonomous robot mobilised by the combined use of twelve servo motors for evaluation of its gait. The electronic design also facilitated interchangeable electrical systems for expansion and continued development of its control and motion. An initial direction for the robot to follow was provided by a wireless controller to the onboard navigation system. The navigation system then performed mathematical calculations based on the robot’s triangular footprint, to determine which leg to move, in order to proceed in the required direction. The tri-pedal stance inherent in the robot’s footprint, allowed each of the robot’s steps to be directed toward one of three directions. It was found that the accuracy of following a given heading over time was dependant on the number of steps taken by the robot. The manually programmed leg movements for Spike’s gait were generated from a lookup table, and programmed into the robot’s processors, relating servo motor angular displacement to leg destination position for each orientation of the robot. Spike represents a true example of a simple, but effective concept of motion, which has been crafted in the form of an elegant mechatronics design. The motion of the robot is unique by its simplicity of concept, but may be adapted for development of complicated gaits. It is intended that future expansion of electronic control will provide added research potential, through the development of new sensors and systems, and experimentation with evolved controllers that may subsequently be evaluated on the robot. The final result of this thesis lies with the custom designed six legged robot that successfully implements a unique and novel form of locomotion.

Six legged robotics , Tumbling motion , Motion control , Tripod stance
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