since the hubs 24 and 26 are virtually identical a description of one applies to the other an internal flange 28 on each hub has fastenings 29 removably positioning drive housings 31 and 32 in coaxial position the housings in turn are joined by fasteners 33 to the central housing 34 of a hydraulic drive motor 36 this is not shown in detail but in practice is usually a vane motor or a gear motor receiving and discharging propulsion fluid through ducts 37 and 38 from a suitably controlled standard source not shown but capable of operating the motor 36 in at least one direction at the desired relatively high speed appropriate bearings not shown in the housings 31 and 32 support drive shafts 41 and 42 coupled to the motor 36 for rotation about the axis 23 hubs 43 and 44 are secured to the respective shafts 41 and 42 by keys 46 and 47 and are axially positioned by sleeves 48 and 49 preferably the hubs 43 and 44 are force fitted on their respective shafts and have threaded holes 51 and 52 to permit the use of a standard form of puller not shown for removal additional holding effort is afforded by a pair of washers 40 retained by bolts 39 engaging axial threaded bores 35 in the shafts 41 and 42 seated on the hub 43 and secured by studs and nuts 53 is a carrier 54 concentric with the axis 23 and rotatable with the shaft 41 the carrier is generally circular cylindrical in exterior contour but is provided with one or more in this case.