Neptune 2 robot arm

If I recall correctly - The design for these arms originally appeared in Practical Electronics in the 70s.

They were driven by a 12V motor running a water filled hydraulic system with solenoid operated valves. The Rams (pistons) used a 'rolling' rubber membrane seal to eliminate leaks. Positional Feedback was by LDVT. I can't really recall what the control electronics were based on - but I do remember there being quite an involved analogue section around the LDVTs.....

Hope this helps, Jon.