Full motion home flight simulator.

[The Enlightenment]

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.

[NoHoverStop]

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. However
he's still got to invest in pumps, precision-valves and plumbing and the
maintenance thereof. He'd be better off looking at electric drives, of
the kind that are already busy replacing hydraulics in affordable sims.
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.

[The Enlightenment]

"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.

[Peter Gottlieb]

I would think that the "softness" of an air system would limit its
usefulness. I had heard that there were problems with fluid compressibility
and component expansion on prototype high-pressure hydraulics (over 5000
psi) and air is much worse than that.


"Clark" <stillnospam@me> wrote in message
...
> "The Enlightenment" > wrote in news:gF1wb.23785
> :
>
> [snip]
> >
> > I predict incidentally that compressed air servo systems will replace
> > hydraulics in many aircraft. Safety, economy and ease of service will
> > promote that.
> >
> >
> Ever had one of those air control lines freeze? I have and its not fun...

[[email protected]]

Clark <stillnospam@me> wrote:

>"The Enlightenment" > wrote in news:gF1wb.23785
:
>
>[snip]
>>
>> I predict incidentally that compressed air servo systems will replace
>> hydraulics in many aircraft. Safety, economy and ease of service will
>> promote that.
>>
>>
>Ever had one of those air control lines freeze? I have and its not fun...

Yes, there's that which can be fixed with an air filter and dryer
but air isn't a great medium for 'high effort' actuators like U/C
jacks and even worse for precise movement/high effort units like
flap actuators. You'd need a lot of extra control equipment to
prevent 'over-travel' etc. Doesn't sound like there's much danger
of it taking over any time soon to me.
--

-Gord.

[Robert Moore]

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

Just for your information, the YAK-52s being imported into this
country are pneumatically operated, the brakes, flaps, landing
gear, and even the engine starter. The starter is most unusual
in that the compressed air is injected into the top of the cylinder
heads just past TDC via an air distributor similiar to the spark
system.

Bob Moore

[Tarver Engineering]

"Peter Gottlieb" > wrote in message
t...
> I would think that the "softness" of an air system would limit its
> usefulness. I had heard that there were problems with fluid
compressibility
> and component expansion on prototype high-pressure hydraulics (over 5000
> psi) and air is much worse than that.

Small fast actuators are not an issue in a system simulating the motion of a
cockpit where 2 hertz is the outer limit in the s-plane.

<kook eradication>

[The Enlightenment]

"Peter Gottlieb" > wrote in message >...
> I would think that the "softness" of an air system would limit its
> usefulness. I had heard that there were problems with fluid compressibility
> and component expansion on prototype high-pressure hydraulics (over 5000
> psi) and air is much worse than that.

The problems with the use of compressed air which relate mainly to its
'compressibility' and the 'stiction' of the piston actuators you speak
of have been overcome and highly precise and dynamic pneumatic
positioning systems are now available commerially. These are 'non
linerarites' and modern self tuning and adaptive control systems deal
with them with ease.

A simple PID (Proportinal Integral Differential) controller can
position a pneumatic jack to within +/-1cm. This is clearly not
enough for a flight control surface or a simulator.

This is why pneumatic positioning systems work.
1/ They are closed loop and use a positioning sensor.
2/ The position of the actuator can be used to estimate the
compressibility of the volume in the cylinder.
3/ Use of pressure sensors on the pistons to determin the actual
pressure is obviously expensive so a mathematical model estimates the
pressure.
4/ To get rid of 'stiction' of the piston a 'dither' or samll AC
signal just above resonant frequency is added in to break stiction.
Precision hydraulic use dither as well.
5/ The controller estimates the load and adjusts itself accordingly.

The result is a positioning accuracy of 0.02mm or better.

It isn't even expensive.

Some links for you:
High Steady-State Accuracy Pneumatic Servo Positioning System with
PVA/PV Control and Friction Compensation Abstract
http://robotics.mcmaster.ca/Publications/icra2002_1.pdf

ORIGA-SERVOTEC
Servo-Pneumatic Positioningsystem Series OSP-P
http://www.hoerbiger-origa.com/catalogue/English/OSP-P/OSP-P_E_07_Servotec.pdf

Servopneumatics Can Meet Accuracy Requirements of up to 80% of All
Positioning Applications
http://www.motionshop.com/fluid/pr/festo1.shtml

"Smart" Servopneumatics Positioning Systems
Axis Controller SPC-200
http://www.festo.com/INetDomino/us/en/90f9a46025c5aa98c1256c39005e64b0.htm



>
>
> "Clark" <stillnospam@me> wrote in message
> ...
> > "The Enlightenment" > wrote in news:gF1wb.23785
> > :
> >
> > [snip]
> > >
> > > I predict incidentally that compressed air servo systems will replace
> > > hydraulics in many aircraft. Safety, economy and ease of service will
> > > promote that.
> > >
> > >
> > Ever had one of those air control lines freeze? I have and its not fun...

[The Enlightenment]

Robert Moore > wrote in message >...
> >>> I predict incidentally that compressed air servo systems will
> >>> replace hydraulics in many aircraft. Safety, economy and ease
> >>> of service will promote that.
>
> Just for your information, the YAK-52s being imported into this
> country are pneumatically operated, the brakes, flaps, landing
> gear, and even the engine starter. The starter is most unusual
> in that the compressed air is injected into the top of the cylinder
> heads just past TDC via an air distributor similiar to the spark
> system.

Zoche aero diesels also use compressed air starters. They are lighter
and more reliable (can't short out)

http://www.zoche.de/
"Reliable starting at low temperatures - patented pneumatic start
system provides instant manifold pressure. Cold start and acceleration
to 2,500 rpm within a second has been demonstrated. Start air
reservoir is refilled by a manifold air driven free piston pump. If
necessary this pump can be operated on any 2 bar (28 psi) air supply."

>
> Bob Moore

Focker when they designed the F27 Friendship (as a DC3 replacement)
purposefully avoided Hydraulics. Hydraulics leak oil (air leaks
aren't to bad) and need special technicians. Hydraulic fluid is
expensive, corrosive and is flamable. Engine bleed air can supply a
pneumatic system.

I think under-carriage opperation or even flap positioning isn't too
difficult but I suspect that the highly precise and dynamic
requirements of flight surface positioning and servo assistance is now
within the capability of pneumatic servo positioning systems.

[[email protected]]

(The Enlightenment) wrote:

>Precision hydraulic use dither as well.

Ok...I take back what I said about pneumatic systems...I really
don't know much about them, having only some small experience
with them on a/c up to about 1977. I never did like them I'll
admit.

Your mention of 'dither' in hydraulic systems is true, the
propeller control hydraulics of several a/c that I'm familiar
with use it to make the system react quickly to changing
conditions. Thanks for the links, most informative.
--

-Gord.

[Vaughn]

"The Enlightenment" > wrote in message
om...
> Robert Moore > wrote in message
>...
> >
> > Just for your information, the YAK-52s being imported into this
> > country are pneumatically operated, the brakes, flaps, landing
> > gear, and even the engine starter. The starter is most unusual
> > in that the compressed air is injected into the top of the cylinder
> > heads just past TDC via an air distributor similiar to the spark
> > system.
>
> Zoche aero diesels also use compressed air starters. They are lighter
> and more reliable (can't short out)

Compressed air is also commonly used to start large diesels, such as
used on ships and submarines. Not a new concept!

Vaughn