A drive unit for a rail-guided displacement device comprising: a base part; a housing comprising: a first yoke shaft sleeve and a second yoke shaft sleeve, the first yoke shaft sleeve and the second yoke shaft sleeve being spaced apart and disposed on opposite sides of the base part, and a cross sleeve rigidly connecting the first yoke shaft sleeve and the second yoke shaft sleeve; wherein the housing is pivotally connected to the base part such that the housing can pivot, in use, relative to the base part about a pivot axis; a first yoke and a second yoke, each of the first yoke and the second yoke comprising: a guide wheel assembly, the guide wheel assembly comprising one or more guide wheels arranged to roll, in use, along a running rail; and a yoke shaft; wherein the yoke shaft of the first yoke is received in the first yoke sleeve and the yoke shaft of the second yoke is received in the second yoke sleeve, the yoke shafts being movable longitudinally within their respective yoke sleeve, in use; and a mirror shaft disposed at least partially within the cross sleeve, the mirror shaft providing communication between the yoke shafts in the yoke sleeves and being configured such that when, in use, one of the yoke shafts moves longitudinally in its yoke sleeve the mirror shaft causes the other of the yoke shafts correspondingly to move longitudinally in its yoke sleeve.