Contrary to basic kinematic modelling, during tight turns, wheelchairs can slide sideways by non-negligible magnitudes: Collision risks may be increased.

Small spaces make collision-free turns difficult for wheelchair users. Contrary to basic kinematic wheelchair modelling and not considered previously by engineers; when wheelchairs turn in small spaces, could lateral drift (sideways slipping) increase the risk of collisions with surrounding structures such as walls and doorways? An improved kinematic understanding can inform building design and therapeutic involvement with wheelchair use. Wheelchair lateral drift is investigated. Two experiments with assisted wheelchair use are reported. Weights represented wheelchair occupants. First, lateral drift was measured by motion capture (VICON): turns (n = 225) made by the experimenter, for six radii of curvature (0-613 mm) and four total-masses (81-142 kg). Second, lateral drift was measured by ruler: turns (n = 105) made by experienced wheelchair assistants (n = 22), for three radii of curvature (0, 306, and 800 mm), and self-selected maximum comfortable weights. Lateral drift away from centre of curvature occurred for all radii of curvature greater than 0 mm, and a maximum median lateral drift of 27 mm/rad occurred for 142 kg total mass with 459 mm radius of curvature. Lateral drift increased with mass (r² = 0.68 for 358 mm radius of curvature). During tight turns, lateral drift magnitude and direction is such that it can increase risks of collisions with surrounding structures.

A novel four-caster manual vehicle manoeuvring investigation: Higher loading-weights require larger turning spaces.

Patient-hoists, goods-trolleys and other omni-directional manually operated vehicles are ubiquitous. Yet no substantive, empirically based dynamic analysis has been made of these four-caster vehicles despite manual handling concerns. A relationship between loading-weight and turning space is indicated by theoretical analysis which further shows that this effect is represented by only 11 different manoeuvres. A qualitative account of the theory is presented. These 11 manoeuvres were implemented experimentally. A total of 17 subjects selected a maximum comfortable loading-weight for the four-caster vehicle for each of the 11 manoeuvres. Vehicle displacement and handle forces were measured for different centres of zero velocity. The median loading-weight of the manoeuvre with the highest loading-weight selections was 101% greater than the mean loading-weight of the three manoeuvres with the lowest loading-weight selections. The manoeuvre with the highest loading-weight selections required a larger vehicle turning space: one dimension increased by 37% (173 mm) compared with the three lowest loading-weight selection manoeuvres and the other dimension increased by 17% (130 mm) compared with one of the lowest loading-weight selection manoeuvres. Higher loading-weights require larger turning spaces. These results can contribute to building designs which facilitate safe manual manoeuvring of four-caster vehicles.