Developing a Free-Falling Robotic Cat With Righting Reflex

Abstract

Changing the orientation of a body in free fall is a useful skill, found in cats. The applicationsrange from zero-gravity in space to damage control of a falling object. This thesis aims to create arobot cat able to always land on its feet. The robot cat is based on the rotating cylinder conceptsuggested by Kane and Shere, where the front and the rear of the cat each consists of a larger outercylinder rotating around a smaller inner cylinder, connected by a revolute joint. Each half of therobot cat consists of a PE100 outer pipe, an aluminum inner tube, a servo motor, an incrementaloptical encoder, and a power supply, connected by 3D printable parts. A Pixhawk 4 Mini is usedas the control unit, and an Arduino nano and a quadrature counter are used to read encoder data.The results involve concept generation and selection. Suitable components are identified and se-lected. A design is proposed, implementing the components to the concept. Communication be-tween devices is achieved using SPI and UART. Hobby servo motors are modified, calibrated andlinearized using the least-squares approximation. System identification is performed using blackboxfrequency analysis, and a state-space velocity control system is suggested. This provides a goodfoundation for further development.