piston 17 through a flexible hydraulic fluid transport hose 31 and into a hydraulic muscle 32 hydraulic muscle 32 contracts as it receives hydraulic fluid attachment structure 33 is pulled and can be used to pull a load such as is necessary when flexing a robot arm also as electronic control circuit 19 moves magnet 15 towards sealing piston seat 18 of tube 13 hydraulic fluid is drawn by piston 16 into tube 13 from a flexible hydraulic fluid transport hose 34 and out of a hydraulic muscle 35 this allows hydraulic muscle 35 to relax and be extended as can be seen by the above discussion hollow tube 13 needs to be sufficiently large to provide a volume of hydraulic fluid to hydraulic muscle 32 so that hydraulic muscle 32 can sufficiently contract a desired amount and to provide a volume of hydraulic fluid to hydraulic muscle 35 so that hydraulic muscle 35 can sufficiently contract a desired amount a feedback sensor 38 electrically connected to electronic control circuit 19 can be used to monitor extension of attachment structure 36 this can allow electronic control circuit 19 to precisely control movement while in fig1 feedback sensor 38 is shown positioned to monitor extension of attachment structure 36 feedback sensor 38 can be located at.