Dynamics and Control of a Steer-by-Wire Bicycle

Abstract

Already for some time, electronic enhancements regarding vehicle behavior has made its way into the aviation and automotive industry by the term "by-wire" technology. Electronic sensors and actuators are used to replace traditional mechanical systems in which software is used to operate the actuators in a way that is not possible with traditional mechanical systems. The use of steer-by-wire technology can also offer great opportunities on single-track vehicles like motorcycles, scooters and bicycles. Single-track vehicles can be highly unstable, especially at low forward speeds and they require a relative high amount of rider control. By replacing the mechanical connection between the handlebar- and steering-assembly with electronic actuators, a controller can be used to control the dynamic behavior of the bicycle based on additional sensor information. This research has focused on the modeling and simulation of a steer-by-wire control strategy to modify and enhance the lateral stability of a bicycle at low forward speeds. Case studies show additional capabilities of a steer-by-wire system on bicycles to influence its dynamic behavior, by providing a dynamic response comparable to a bicycle with a virtually different geometry or even the ability to stabilize an inherently unstable bicycle. A steer-by-wire bicycle prototype was designed and build by replacement of the mechanical connection between handlebarand steering-assembly by electronic actuators and a custom digital controller. The steer-bywire bicycle prototype equipped with sensors, measuring the forward speed- and roll-rate is subsequently used to experimentally evaluate the proposed control algorithms. Test results obtained from experiments conducted by the steer-by-wire bicycle prototype equipped with a stabilizing controller algorithm, show the ability to stabilize the lateral motion of the bicycle-rider combination at low forward speeds as predicted by numerical simulations. Rider steer effort is reduced which makes the bicycle more easy to ride and could lead to future implementation on bicycles tailored for elderly or those physically impaired. The importance of steer torque feedback is indicated by comparison of steer effort measurement results between experiments with and without steer torque feedback at the handlebar.