An assisted propulsion system method and chassis for conveying a payload along a surface are described. A plurality of wheels (62) are disposed about the chassis (60) for supporting the chassis on the surface (S). A drive (20) is arranged to provide at least assisted propulsion to the chassis (60) along the surface. At least a driving part (21) of the drive (20) is connected to the chassis (60) via a mount (30) having a resiliently sprung link (31) at least the driving part (21) of the drive (20) having a fixed orientation and being moveable independently of the chassis (60) and the plurality of wheels (62) in a direction towards the surface the resiliently sprung link (31) being arranged to direct the at least the driving part (21) of the drive (20) onto the surface during provision of said assisted propulsion. A sensor is arranged to monitor acceleration of the drive and to communicate data on said acceleration to a controller the controller controlling operation of the drive in dependence on the data received from the sensor.
