Sisu Nemo is a hydraulic radial piston motor type developed and initially produced by Suomen Autoteollisuus (SAT). The system was patented in 1961. The motor produces a high torque at low speed and it has been primarily used to power both civil and military lorry trailers. A number of other applications have been designated for various industrial applications. Development The idea of the motor came from DI Ilmari Louhio who worked in SAT as design engineer. The operating principle was so simple, that when Louhio presented his invention to the technical department and company management, he was not taken seriously; the answer was "if that would work, someone would have invented it for long ago". However, Louhio didn't give up and in 1959 a team was set up to develop the concept. The members were Louhio, Pentti Tarvainen, Antti Saarialho and Lasse Airola; in addition, dozens of people from different departments took part in the development work. A number of prototypes were built and put through intense testing before the design was ready for production. The first field test took place in autumn 1960, with a Fordson Major tractor pulling a hydraulically driven trailer. A patent was granted for the invention in January 1961, which was named Nemo, from nestemoottori ("fluid motor"). Operating principle The motor contains five fixed radial hydraulic cylinders, whose pistons end in rollers that in turn press outward against a ring whose inner profile consists of eight cams. As the pistons expand in turn, the rollers force the ring to rotate, a full rotation occurring after 8 strokes from each piston. The hub consists of a distribution valve that adjusts the flow in and out of each cylinder. A drum brake may be integrated with the motor and the combined unit fitted into a 20-inch rim. Despite its small size, the system can deliver 8 000–10 000 newton metres of torque, so a separate planetary gear set is generally not required. Due to the large number (40) of piston movements per rotation, the torque is also smooth. If the pistons are all withdrawn into the hub, the rollers are not in contact with the cam ring, and the wheel can freewheel. The system also contains a twin pump unit attached to the free end of the towing vehicle engine. One of the elements can be bypassed, which halves the transmission ratio. Applications Logging trucks The first