Load handling devices and methods provide for lifting and moving one or more containers stackable in a storage and retrieval system. The storage and retrieval systems include a grid structure comprising grid members that are arranged in a grid pattern for guiding the movement of load handling devices on the grid structure, each load handling device including a wheel assembly with first and second sets of wheels for engaging with the grid members to guide movement of the load handling device in first and second directions, respectively. Application of force to a belt causes a traveller to move along a rail, such that the movement of the traveller from a first position to a second position causes the respective set of wheels to be lowered or raised.