Speaker: David Limebeer, University of Oxford, UK, USA

Title: Suppression of Burst Oscillations in Racing Motorcycles

Abstract: Burst oscillations occurring at high speed, and under firm acceleration, can be suppressed with a mechanical steering compensator that replaces the conventional steering damper. Burst instabilities are the result of interactions that occur between the wobble and weave modes under high-speed firm-acceleration conditions. Under some operating conditions the wobble-mode frequency (of the subject motorcycle) decreases, while the weave mode frequency increases until destabilizing interactions occur.

The design analysis is based on a timeseparation principle, whereby bursting is assumed to occur on time scales over which speed variations can be neglected. Even under braking and acceleration linear time-invariant models corresponding to constant-speed operation can be utilized in the design process. The influences of braking and acceleration are studied using d’Alembert-type inertial forces that are applied at the mass centres of each of the model’s constituent bodies.

The resulting steering compensator is a simple mechanical network that comprises a conventional steering damper in series with a spring. In control theoretic terms, this network is a mechanical lag compensator. Given the inevitable uncertainties in the motorcycle model, in combination with nonlinearities that occur over a wide range of operating conditions, a robust control framework was chosen for the design optimization. The optimization process ensures improved performance over the machine’s entire operating regime.