While I was researching pneumatic positioning systems I came across
this web site which may be of interest to rec.aviation.military. It
looks like a German Kid who's putting together a full motion flight
simulator as a cooperative 'open source project' that is affordable
for a home user.

http://www.cadsoft.de/people/kls/fltsim/index.htm

This is some background on the technology :

6.5 bar (100psi) air has a great tradition for use in Industry because
of its cheapness, clean nature and power. Several years ago the FESTO
company brought out pneumatic positioning systems using a 5/3 way
analog servo valve. With modern control electronics pneumatic servo
systems can now position with full force against a disturbance to
within an amazing 0.02mm. The analog servo valves cost about US$500
however by using normal 5/3 way solenoid valves and pulsing them (PWM
pulse width modulation) almost the same accuracy (0.2mm) can be
achieved for US$50.00

I predict incidentally that compressed air servo systems will replace
hydraulics in many aircraft. Safety, economy and ease of service will
promote that.