Analysis and Design of a Passive Steering Mechanism for a Pedaled, Self Balanced Unicycle

Abstract

In this paper, a pedaled, selfbalanced vehicle named Legway, is developed. The vehicle is structurally similar to a pedaled unicycle but uses a brushless DC (BLDC) hub motor as its main driving wheel. It is intended that the unstable longitudinal dynamics of the vehicle is stabilized by a feedback control system, but the lateral balancing and steering are manually controlled by the rider via a passive steering mechanism. This study is first devoted to the dynamic modeling of the steering mechanism. It is shown from analyzing the model that there is a critical speed beyond which the unicycle becomes openloop stable in the lateral direction so that the rider can turn the handle to steer the unicycle as the conventional bicycle. The dynamic model is then used for conducting simulations for selecting appropriate design parameters. An experimental prototype is constructed based on the analysis result and the steering performance is experimentally verified.