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
Hope this helps,
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