Modelling the stability and maneuverability of a manual wheelchair with adjustable seating

Manual wheelchairs are generally designed with a fixed frame, which is not optimal for every situation. Spontaneous changes in seating configuration can ease transfers, increase participation in social activities, and extend reaching capabilities. These changes also shift the centre of gravity of the system, altering wheelchair dynamics. In this study, rigid body models of an adjustable manual wheelchair and test dummy were created to characterize changes to wheelchair stability and maneuverability for variations in backrest angle, seat angle, rear wheel position, user position, and user mass. Static stability was evaluated by the tip angle of the wheelchair on an adjustable slope, with maneuverability indicated by the ratio of weight on the rear wheels. Dynamic stability was assessed for the wheelchair rolling down an incline with a small bump. Both static and dynamic simulations were validated experimentally using motion capture of real wheelchair tips and falls. Overall, rear wheel position was the most influential wheelchair configuration parameter. Adjustments to the seat and backrest also had a significant impact on both static and dynamic stability. For wheelchairs with a more maneuverable (or 'tippy') initial configuration, dynamic seating changes could be used to increase stability as required.