frame structure 102 and extends inwardly towards the mast 12 a set of rollers 111 is mounted on each support 109 the rollers 111 on the supports 109 surround and engage the rails 32 a drive mechanism 110 is mounted on each supporting plate 106 each drive mechanism 110 includes a motor 112 having an output shaft 114 shaft 114 extends through a bushing on the supporting plate 106 and has a gear 116 keyed to its other end gear 106 engages a pair of vertically spaced pinions 118 that are in mating engagement with the rack 40 rotation of the shafts 114 by the motors 112 imparts rotation of the pinions 118 via the gears 116 this of course allows the motor trolley 100 to advance along the rack 40 and hence along the mast 12 a shock absorbing arrangement acts between the framework 22 of the elevating platform 16 and the motor trolley 100 to provide a floating couple therebetween as can be seen the shock absorbing arrangement includes a c shaped member 120 having a web 122 and upper and lower limbs 124 and 126 defining a channel therebetween the web 122 is welded to the main upper beam 76 of the framework 22 an elastomeric shock absorbing element 128 is secured to the upper limb 124 and is positioned within the channel the cross member 108 of the motor trolley 100 is accommodated within the channel and forms an interference fit with the elastomeric shock absorbing element 128 and the lower limb 126 in operation when the motors 112 are actuated to.