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PatriciaJB
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Posted: Wed Aug 29th, 2007 07:39 pm |
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Kjell asked: "Have you looked at pneumatic muscles ?"
Hi Kjell,
Yes, I looked at various types of pneumatic muscles about 3 years ago but they were either not suited to continuous flapping or they were too slow to recover....or the entire pneumatic system would have been too heavy.
I haven't looked at them since so I don't know whether they've improved or not.
Pity they didn't work out....I quite like the idea of man-made muscles.
Cheers,
Patricia
Last edited on Mon Feb 25th, 2008 04:42 am by PatriciaJB
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Flapper Fan
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Posted: Wed Sep 12th, 2007 03:16 am |
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I have studied this type of actuator and believe that it is the way to go. I prefer a liquid drive with pneumatic accumlator for the best power stroke. I have built a few crude systems and find it promissing for several reasons. Good power to weight ratio, load limiting and shock absorbtion, low speed to match flap cycle speed, etc. I would like to disscuss this further with anyone wishing to persue this application.
Grant Smith
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PatriciaJB
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Posted: Wed Sep 12th, 2007 02:41 pm |
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Hi Kjell and Grant,
I'm very interested in this but am still looking at Kjell's Festo link so can't respond until I've brought myself up to date [so far, I can see that pneumatic muscles have improved greatly since I last looked at them  ]
Could you tell us more about your experiments and findings, Grant ?
Kjell, have you done any experiments with them ?
Cheers,
Patricia
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Flapper Fan
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Posted: Fri Sep 14th, 2007 12:23 am |
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Patricia,
For my first attempt, I used hollow braided polyester rope of fairly large diameter, 3/4 inch I think, similar to what is used for auto towrope with hooks attached at either end. I inserted a length of rubber surgical tubing with a tire valve or 1/4-inch brake line safety wired into the end for connection to a pressurized tank of water. I used the standard water fire extinguisher about 9 inches in diameter and 2 1/2 feet tall. You can safety wire the surgical tubing directly to the fire extinguisher nozzle. My test piece was about 3 1/2 to 4 foot long free length (not pressurized and not stretched). My power supply was a standard air compressor capable of 100 to 110 psi. A weight of about 50 pounds was all that I could support without pulling out fittings and would extend the rope to about 5 foot length.
When pressure was applied without the weight attached the length would reduce to about 60% of the free length. Attaching a 40-pound weight would extend the rope in a spring like fashion about 8 to 10 inches if the pressure was held constant. If water is used in the actuator, and the valve is closed, prior to adding the weight, the pressure will rise when the weight is added and the spring rate becomes considerably stiffer, roughly two times I would say.
A force versus pressure diagram is nonlinear as a function of length as the braid becomes radial and less axial as the rope shortens. This produces a high force at long lengths and less force as the rope shortens. I believe this is desirable for typical beam and actuator geometry.
Perceived Advantages:
Very light weight for a given force X distance. A piston actuator would weigh at least 3 times as much.
The spring rate will provide some gust load alleviation.
Control of force via pressure rather than displacement via ridged linkage will eliminate many structural problems and allow a much lighter wing structure and drive mechanism.
Reaction time was very fast (perhaps too fast) and is not restricted to the sign wave motion of a crankshaft mechanical system.
Disadvantages:
The braded rope was a course weave and high pressure would blow the rubber liner through the braid and cause a rupture.
Special fittings will need to be manufactured for end fittings. High pressure would blow or pull the rubber tube off the fitting.
Friction and motion between the (rubber) pressure chamber and the tensile (rope) fibers may become an issue.
Summery:
The experiment was crudely constructed and failed prior to formal data analysis. However, it provided useful insight into the characteristics and overall was successful and encouraging.
Conclusions:
The anticipated problems are solvable by an armature builder and well within state of the art construction and materials.
A similar system operating at 3,000 psi (if possible to develop) could provide a light-weight and suitable ornithopter drive system.
Data obtained via this experiment was very crudely obtained and should not be relied upon for future design studies. Further development and test is required to verify performance and specifications for the system intended to be used.
Additional Activities: See follow-on reports for subsequent investigations.
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Flapper Fan
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Posted: Fri Sep 14th, 2007 12:48 am |
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Patricia,
I have made additional samples of braded nylon and braded steel mesh with good results. These materials have a much finer weave than the original polyester rope and do not tend to “blow out” as was the primary problem with the original at any pressure greater than 30 to 40 psi. These examples were much smaller in diameter all less than ½ inch free diameter. There is a wide range of braided material to select from and this will have a significant influence on overall characteristics. I have a valve, accumulator, and actuator control mechanism in mind but have not manufactured any hardware to date.
I have (in thought) gone back and forth between further development in either model or full scale and believe that full scale is the way to go in order to avoiding solving the problems three or four times in different scale.
I consider this work complete until I have an airframe that requires further hardware development. The airframe will be developed with the required joints and hinges however, it will have Kevlar, Carbon or steel lines in place of the actuators for gliding flight and control studies prior to instillation of any actuators. I do not believe conventional stability and control solutions are adequate for an operational ornithopter.
Grant
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murray
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Posted: Wed Oct 3rd, 2007 12:12 pm |
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Hi Grant,
I played with similar actuators operating at very low pressures in my quest for pitch-stabilising wing articulations. These were made of a collapsed plastic bag stuffed into the sort of plastic net in which you buy oranges. Not ideal and a bit frictional but it served to demonstrate that for low pressure actuators you need a big volume of air to blow in and out each cycle, so viscous losses in the vent pipe were a real consideration.
For a given stroke energy there is obviously an optimal compromise between high pressure (and attendant strength and weight of pipes, pumps, fittings and possibly liquid operating fluid) and high flow (with large diameter actuator mesh, delivery pipes and pumps and the thermodynamic losses of compressing and expanding air).
Overall, if your power source initially develops linear or rotary motion, I believe converting that to hydraulic flows and back through piston or "hydraulic muscle" actuators will be considerably heavier and less efficient than pulleys and tensile cables which act very much like animals' sinews. Hydraulic actuators are more likely to be useful for control motions than for flapping power, as for example on the articulated tip panels of the Exulans foot-launched glider.
The reason real muscles are so interesting is that the power is developed in the muscle structure itself from biochemical reactions, which allows animals to deploy decentralised power sources where they are needed with small diameter piping for the fuel (blood). Even so, looking at birds and bats etc. we see that the flight muscles are mostly inboard with sinews (cables) conveying the motion to lightweight distal articulations.
Murray Scott.
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Flapper Fan
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Posted: Thu Oct 4th, 2007 10:10 am |
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murray wrote:
For a given stroke energy there is obviously an optimal compromise between high pressure (and attendant strength and weight of pipes, pumps, fittings and possibly liquid operating fluid) and high flow (with large diameter actuator mesh, delivery pipes and pumps and the thermodynamic losses of compressing and expanding air).
murray,
I agree with your comments and add the following concerning the above quote.
In general the higher the pressure the lighter and more efficient the system is for a given power capacity. The thermodynamic losses of compressed gas dictates the use of a liquid for power transfer. This is the path I am planning.
The big hit for weight is the motor and pump system. I hope to lighten that system considerably with a direct conversion internal combustion hydraulic motor pump therby eliminating the weight of rotating components and obtaining the speed reduction through hydraulic accumulator (bladder type) to also eliminate the typical gear box required of the conventional piston engine. System development could use pneumatic stored energy for short duration powered flight without the specialized power supply.
Direct conversion of a sugar solution fuel to actuator force would be wonderful if deveoloped.
Grant
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Sigurd
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Posted: Fri Mar 20th, 2009 01:27 pm |
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Hello, Flapper Fan
Could you tell me more about the bladders and meshes you have found suitable for the muscles?
I had thought spectra/dyneema would be great for the mesh, it has very high abrasion resistance, is super slippery and is one of the strongest fibers inside existence, density is 1.
Do you think it would be inefficient to expand steam directly in the muscles? Not sure if any bladder material is suitable for elevated temps - and spectra would have to be insulated from the steam temp. Insulating steam pipes with light foam or refractory mat could marginalize the heat losses?
I don't know much about pump sizes, weights, and efficiencies. Are piston pumps more efficient than rotary ones? I am looking into building a carbon/carbon Tesla turbine and powering a rotary pump from it - small and light powerplant, but maybe your plan is better, with the IC piston to hydraulic piston?Last edited on Fri Mar 20th, 2009 01:30 pm by Sigurd
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Sigurd
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Posted: Fri Apr 3rd, 2009 02:28 am |
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| Bosch Rexroth bellows actuators. Last edited on Fri Apr 3rd, 2009 02:28 am by Sigurd
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Flapper Fan
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Posted: Sun Apr 5th, 2009 01:05 am |
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Sigurd wrote: Hello, Flapper Fan
Could you tell me more about the bladders and meshes you have found suitable for the muscles?
I had thought spectra/dyneema would be great for the mesh, it has very high abrasion resistance, is super slippery and is one of the strongest fibers inside existence, density is 1.
Do you think it would be inefficient to expand steam directly in the muscles? Not sure if any bladder material is suitable for elevated temps - and spectra would have to be insulated from the steam temp. Insulating steam pipes with light foam or refractory mat could marginalize the heat losses?
I don't know much about pump sizes, weights, and efficiencies. Are piston pumps more efficient than rotary ones? I am looking into building a carbon/carbon Tesla turbine and powering a rotary pump from it - small and light powerplant, but maybe your plan is better, with the IC piston to hydraulic piston?
As previously mentioned I have not done extensive testing of various materials. I have only done enough to convince me that this is a promising area to pursue. All bladders were surgical rubber tubing. The tube was inserted inside a braid and the ends secured with a hose clamp around a tire valve or wood plug. This was done many years ago so numbers may not be accurate. The rubber tube measures 7/16 OD and 1/16 wall. I have used ½ inch (I believe) hollow braded poly rope in one instance and a steel mesh in another example. The poly rope is quiet course and will allow pressures to about 35 psi. With higher pressure the rubber tube would blow out through the holes in the poly braid. The steel braid would approach 100 psi if the end fittings could be kept from a blow out. A three-foot length of steel braid would lift about 35 pounds and contract about 9 inches or more. Again the limiting factor was the end fitting. There is a reasonable amount of stretch and non-linear force so a stress-strain map versus pressure is required. My fittings failed on the steel braid due to inertia loading of the 35-pound weight before much data was taken but the load to weight ratio was impressive as demonstrated by failure of the fittings. A sturdy and reliable end fitting will be key to a successful design.
Commercial hardware is now available but may not be suitable for the sizes needed for a full size ornithopter.
I have a renewed interest in this area and may be doing more work in the not too distant future. I have several types of braid but no Kevlar braid. I have Kevlar filament but expect a commercial braiding machine would be needed to get a consistent product.
I am sure steam would work if you had suitable high-temperature materials. I plan to use an air tank for short duration trials.
A piston pump is generally heavier than a rotary pump but more efficient and capable of higher pressure. The mussel can also be used as a compressor but does not appear to be very efficient in that capacity.
I intend to use water (or other liquid) as a working fluid and compressed air (or other gas) for an accumulator. One could use a high- pressure water pump such as used for pressure cleaning. I hope the final design would be able to operate at 2,000 psi or more.
The accumulator setup allows a smaller pump and motor and the accumulator is used for takeoff and short duration climb. I think the overall power system should not weigh any more than gears and a mechanical linkage. Structural savings should be possible because the pressure and spring effect eliminates high G load due to gusty conditions.
I have just reviewed my prior post dated Sept 13, 2007 and the numbers given there are probably more accurate.
Last edited on Sun Apr 5th, 2009 01:15 am by Flapper Fan
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Sigurd
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Posted: Sun Apr 5th, 2009 08:03 am |
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I found some "high" temp rubber that would be enough for saturated low pressure steam. I think silicone is going to allow proper steam pressures and temps.
Soller composites has braided carbon socks, maybe also kevlar. I am concerned for friction wear in the braid (kevlar wears through itself - not so with spectra/dyneema - but those don't tolerate heat - is it possible to insulate the inside of the braid? A fat sock of unimpregnated glassfiber?) and against the bladder.
I have not found a lot of free piston IC engines, some pile drivers use diesel. I guess that it can be a bit finicky to make work without the flywheel and without some knowledge - otherwise why all the extra parts in normal rotary piston IC compressors and pumps?
Two opposed free pistons in the same cylinder would be neat and might give lots of power.
I have been reading about Tesla turbines. I also read about two TT's used as fluid transmission.
Recently I have been looking at thermoacoustic compressors - could work as a pump as well. And even el.gen - http://www.io.com/~frg/ ... 5kw/kg, amazing for such a simple, apparently quiet(!!!) device.
Thanks for your reply, please keep me updated on your progress.
Edit: I read about testing of a hydraulic transmission in a Huey heli - it was lighter and gave less vibration and similar efficiency.
Edit: I found spectra sleeve; Composite Shoe for Giraffe.
dyneema, 11mm (dia or width?) sleeve (also have technora hollow braid - high temp)... for 12-16mm ropes, probably expands more... having problems finding unreinforced high temp silicone hose.
Edit: Found this instructable about pneumatic muscles. one more: Overall, air muscles can be constructed in all sorts of lengths and diameters to suit a wide variety of applications where high strength and light weight are critical. Their performance and longevity varies according to several parameters regarding their construction:
1) Length of muscle
2) Diameter of muscle
3) Type of tubing used for bladder- testing I've read states that latex bladders tend to have a longer service life than silicone bladders, however some silicones have greater expansion rates (up to 1000%) and can hold higher pressures than latex (much of this will depend on the exact tubing specification.)
4) Type of braided mesh used- some braided meshes are less abrasive than others, improving bladder life span. Some companies have used a spandex sleeve between the bladder and mesh to reduce abrasion. A tighter woven mesh allows for more even pressure distribution on the bladder, reducing stress on the bladder.
5) Pre stressing of the bladder (the bladder is shorter than the braided mesh)- this causes a reduction of contact area (and hence abrasion) between the bladder and braided mesh sleeve when the muscle is at rest and allows the braided mesh to fully reform between contraction cycles, improving its fatigue life. Pre stressing the bladder also improves the initial contraction of the muscle due to initial lower bladder volume.
6) Construction of muscle end housings- radiused edges reduce stress concentrations on the bladder.
Also gave this link to commercial muscle. cool vids
Edit: 450F unreinforced high purity silicone tube at mcmasterLast edited on Wed Oct 21st, 2009 08:28 pm by Sigurd
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Sigurd
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Posted: Wed Oct 21st, 2009 07:48 pm |
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Does anyone have a good idea how to measure the length of the muscle? Possibly, a linear response may not be required.
Fluid could be made conductive or capacitive..?..
knitted resistorLast edited on Thu Oct 22nd, 2009 03:52 am by Sigurd
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Sigurd
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Posted: Mon Oct 26th, 2009 07:33 pm |
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Anyone know about small valves, maybe 3mm inner dia? superlight, for model? diy possibilities?
Fold a hose with a servo?
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TedGM
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Posted: Thu Nov 19th, 2009 11:44 am |
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Hi Sigurd,
You can try (DIY) to get the valve of disposable lighter. I used to play with it. It 's éasy to remove and modify to your needs. You can connect it to the servo by making your own extended lever.
Ted
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Sigurd
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Posted: Thu Apr 22nd, 2010 12:19 am |
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Cool idea with the lighter.
Found out about a different alternative to the braided muscles; pleated ones.
The links say they have less friction (less hysteresis and wear), and can contract more than webbed PAMs.
The membrane is very little stressed except in longitudal axis. Maybe one way to produce a high pressure muscle is to use a thin membrane, surrounded by (and glued to) longitudal strings? Because, if only a thick membrane is used, the kinks would become problematic?
http://lucy.vub.ac.be/publications/Daerden_Lefeber_IJFP.pdf
different types of PAM, same authors
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.89.6717&rep=rep1&type=pdf
more extensive (ph. D)
http://lucy.vub.ac.be/publications/Daerden_PhD.pdf
about valves and sensors
http://www.epsrcham.org.uk/Papers_files/Ham12.pdf
A patent about terminator design, probably more for webbed actuators:
http://www.freepatentsonline.com/5014600.pdfLast edited on Thu Apr 22nd, 2010 12:36 am by Sigurd
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