Theory and validation of the motion resistance mechanism of four-caster manual vehicles

The four-caster manually manoeuvred vehicle is a crucial device for goods movement and disability transport. While there are manual handling related health and safety concerns, no dynamical theoretical-empirical investigation exists. Theoretical examination demonstrates that, in loose terms, the motion resistance effects are affected by vehicle-frame translational velocity direction: the proportion of the moment effect to translational effect produced by motion resistance varies in a highly non-linear way depending on the vehicle-frame velocity direction. An empirical study is devised from the theory. As the intention was to investigate the presence of this phenomenon in real use, human operators were used: they made planar manoeuvres from static equilibrium with a self-selected load while attempting to maintain 11 (maximum) different centres of zero velocity which related to the velocity directions. Results demonstrate that (1) the proportion of moment motion resistance effect to translational motion resistance effect does vary and (2) it is motion resistance rather than inertial forces which are the first-order effect. These results are an essential first step in understanding the manoeuvring difficulties and health and safety issues which arise with these vehicles.