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#1
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Full motion home flight simulator.
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. |
#2
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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. |
#3
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"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. |
#4
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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... |
#5
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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. |
#6
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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 |
#7
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"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 |
#8
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"Peter Gottlieb" wrote in message et...
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/catal...7_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/e...39005e64b0.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... |
#9
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Robert Moore wrote in message .8...
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. |
#10
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