of the other cylinder of each pair being symmetrical or identical in fig3 and 4 the cylinder is indicated by 3 and the motor by 13 the motor 13 has an axis a a substantially perpendicular to the axis b b of the cylinder 3 the motor 13 is supported inside a box 17 consisting of two portions 17a and 17b coupled together in a sealed way the box 17 is supported by two shafts 19 and 21 which project from the closure disks 3b of the cylinder 3 and are firmly attached to the structure 23 of the machine in this way the box 17 is fixed with respect to the casing of the machine while the cylinder 3 is free to rotate for this purpose the cylinder 3 support bearings are mounted on the shafts 19 and 21 the bearings 25 mounted on the shaft 19 may be seen in fig3 the bearings on shaft 21 being disposed in a substantially symmetrical way the two shafts 19 21 are hollow to permit the passage of the motor supply line and if necessary the cooling air suction means which keep the interior of the box slightly depressurized may advantageously be used for cooling the motor 13 is attached by a flange to a flat portion 17p of the box 17 from which the shaft 29 of the motor 13 projects a first pinion 31 is keyed to the shaft 29 and engages with a gear wheel 33 supported by an auxiliary shaft 35 firmly attached to the box 17 the gear wheel 33 is supported by means of rollers 36 and 37 by means of thrust bearings 38 a bevel pinion 39 is integral with the gear wheel 33 and in turn engages with a ring bevel gear 41.