Abstract: A drive assembly (22) for a policy (26) comprises a first pulley (26) having a cable (20) passing around part of the pulley circumference. Three relatively small pulleys (30, 32, 34) are mounted on the assembly body (24) and a belt (36) extends around the pulleys. The belt (36) is driven and two of the small pulleys (30, 34) are located on a chord of the first pulley (26) such that tension in the belt (36) tends to bias the belt (36) to bear against the cable (20) as it passes around a portion of the circumference of the first pulley (26) located between the two small pulleys (30, 34). In a further embodiment, a convex support surface (70; 86) is formed by a belt (62) or rollers (92), rather than by the pulley (26). In another embodiment an assembly (150) may be used to drive a ground engaging wheel (164) of an aircraft or vehicle, rather than a pulley wheel (26).