A master controller assembly for a robotic surgery system has a slave robot assembly having a slave surgical grip device providing a grip degree-of-freedom of motion lying in a predefined slave grip plane and a control unit. The master controller assembly has a portable hand-held master input tool operatively connected to the slave robot assembly. The master input tool has a master tool body having a manipulandum surface, to be hand-held by the surgeon's fingers. The master input tool is mechanically unconstrained from the slave robot assembly and has a grip command detector device having an operative portion. The operative portion is manually operable by radially directed pressure action exerted at an operative surface. A sensing assembly detects the radially directed pressure action so that the radially directed pressure action exerted at the operative surface determines a paired slave grip motion action of the surgical slave grip device.