"NoHoverStop" wrote in message
...

The Enlightenment wrote:

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.

100psi pneumatics do not compare favourably with 1500psi (some sims
I've
dealt with) or 3000psi (aircraft) hydraulics in performance terms.
He's
just not going to get the dynamics he needs because of the low
supply
pressure and the compressibility of his chosen working fluid.

Modern control theory and digital contollers mean that pneumatics can
position accuately to within 0.02mm. Compressibility and cylinder
stiction is not longer an problem: the control system compensates.
These things are quite uncanny to experience. You can bash them with
your thumb or even a hammer and they do not budge even for small
cylinders.


However
he's still got to invest in pumps, precision-valves and plumbing and
the
maintenance thereof.

Analog 5/3 servo valves are about US500 (though I've seen an Italian
brand for about $300) as I pointed out however a solenoid coil on/off
valve can do almost as good job by pulse modulating on and off and can
be brough for $30.00/pair. (You would need 6)

As far as the compressor goes; they can be brought for $100 at a local
hardware (made in china). The nylon tiubing is negligable in price.



He'd be better off looking at electric drives, of
the kind that are already busy replacing hydraulics in affordable
sims.

I immagine 'affordable' refers to those texan oil millionaiers in that
case. Electric positioning systems are not cheap either from my
experience.

Oh and he's going to have "hours of fun" trying to integrate a cheap
head-tracked display system also. Top marks for enthusiasm and
effort
though.