Power System for a Humanoid

Student: Nathaniel James Brewer

Supervisor: Dr. Gordon Wyeth

Category: Electrical Engineering Thesis Project

This thesis describes the steps taken to evaluate design and construct a power supply for a mobile humanoid. The power supply must be able to handle the varied loads of the humanoid, which consist of a high average power but also the very high peak power requirements. The GuRoo team at the University of Queensland is aiming to produce a humanoid that is capable of playing soccer. This GuRoo project will continue for a number of years at UQ, with each years students progressing further along with the evolution of the humanoid. The aim for this year was to assemble the systems necessary for the GuRoo to be able to walk.

This thesis presents the design of the power system of the humanoid. One of the difficult tasks was to estimate the power consumption of the humanoid before it was built. It was found that estimates are very perspective and capable of reaching extremes. Even with the help of a full mechanical simulator, it was difficult to get accurate estimates as the rapid change in the mechanical design and walking algorithm led to a corresponding rapid change in the power consumption. A final estimate of 800W for the lower body joints seemed to gain approval from both the mechanical design team and the control systems team. This figure was used in the design of the power system.

A number of Ni-Cd battery packs were made available second hand from the Sunshark team. These consisted of 32, 1.5Ah Ni-Cd cells which in total deliver between 35 to 44V and can source up to 6A for each pack. The desired voltage for the motors drivers was above 32V and to provide the 800W for 20 minutes it was necessary to place four of these packs in parallel. In order to allow the packs to be placed in parallel and to ensure even current sharing, this thesis details a parallel scheme that uses buck converters on each battery pack to control both the output voltage of the system and the current sharing between the packs. The final product is able to deliver over 1kW of power and from latest estimates should be able to power the GuRoo for over 20mins, or one half of the Robo Cup Humanoid soccer league game.

Poster Presentation (PDF)

Thesis Document (PDF)