Rider control identification in cycling taking into account steer torque feedback and sensorial delays

Abstract

Experimental data were obtained from riding a steer-by-wire bicycle on the open road while perturbing balance with impulsive forces at the seat post (lateral pertubations) as well as perturbing balance with impulsive torques at the steering assembly (steering pertubations). The experiments were conducted at 2.6–5.6 m/s covering both the stable and the unstable forward speed range. For the lateral pertubation experiments two conditions were explored; normal steering and reduced torque feedback steering. Three metrics are used to assess the effect of torque feedback on rider steer control and balance. Results failed to indicate any statistically significant difference between experimental conditions. Bicycle and rider mechanics have been modeled using the Whipple bicycle model extended with the rider inertia. A rider control model is developed that incorporates all of human's sensory pathways and includes a strategy to compensate for sensory dead time. The identified rider control parameters, stabilize the system and mimic realistic rider control behavior. From the results the importance of the torque feedback pathway is strongly indicated. Finally for the steering pertubations the rider control model is modified to account for the cocontraction mechanism. The model manages to approximate the rider measured response and simultaneously captures the significance of the intrinsic response. A high level of intersubject variability is exhibited. The hypothesis that this variability is in fact due to the modulation of admittance in the shoulder joint is strongly suggested.