In this paper, an experimental validation of some modelling aspects of an uncontrolled bicycle is made. In computer models, many physical aspects of the real bicycle are considered negligible, such as the flexibility of the frame and wheels, play in the bearings, and precise tire characteristics. The admissibility of these assumptions can be checked by comparing experimental results with numerical simulation results. The numerical simulations are performed on a benchmarked bi- cycle model . This model (Fig. 1) consists of four rigid bodies connected by revolute joints. The contact between the knife-edge wheels and the flat level surface is modelled by holonomic constraints in the normal direction and by non-holonomic constraints in the longitudinal and lateral direction. In the absence of a rider we assume no-hands operation. This system has three velocity degrees of freedom, the roll, the steer, and the forward speed. For the validation we consider the linearized equations of motion for small perturbations of the upright steady forward motion. Apart from flexibility and play, the greatest uncertainty to be verified in this model is the replacement of the tires by ideal rolling knife-edge wheels.
The experimental system consists of an instrumented bicycle without rider. Sensors are present for measuring the roll rate and the yaw rate, the steering angle and the rear wheel rotation. Trainer wheels prevent the complete fall of the bicycle for unstable conditions.
Measurements are recorded for the case in which the bicycle coasts freely on a level surface. From these measured data eigenvalues are extracted by means of curve fitting. These eigenvalues are then compared with the results from the linearized equations of motion of the model.
As a result, the model appears to be fairly accurate for the low-speed low-frequency behaviour.