hydraulics

Already sent this once but didnt show up, has anyone tried using hydraulics for operating retracts instead of compressed air bottles? it
would be quite easy to do using clinical syringes and a small motor drive with micro limit switch's. A small motor working a rack and pinion to operate the master cylinder which connects to two rams on the u/c legs all made from polypropylene syringes would be light and practically maintanance free with no need for air bottles or recharging, have a drawer full of syringes of different sizes which I use for glue and oil etc so may play around with the idea, the long thin 1ml syringes would make excellent rams strengthened with thin wall brass tube on the outside,
regards, Terry
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I haven't heard of anyone using hydraulics, but you can bet that someone has at some point.
Hydraulic fluid weighs more than air, plus you need a pump and a power source. Weight is critical in our models. I don't see it as a practical solutions for average sized models. Maybe on some monster scale bomber?
Ed Cregger
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On Tue, 13 Feb 2007 11:45:54 GMT, Terence Lynock (MSW)

I haven't heard of anyone doing that, but it sounds like it might be a workable system.
A few nay-sayers from the past:
<http://groups.google.com/groups?as_q=hydraulics&num &scoring=r&hl=en&as_epq=&as_oq=&as_eq=&as_ugroup=rec.models.rc.air&as_usubject=&as_uauthors=&lr=&as_drrb=q&as_qdr=&as_mind=1&as_minm=1&as_miny81&as_maxd&as_maxm=2&as_maxy 07&safe=off>
                Marty
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A small geared motor working a push-pull rack and pinnion connected to the plnnger of a 4 ml syringe which in turn feeds two 2 ml syringes would give ample power to raise or lower a couple of u/c legs weighing a couple of ounces each, you have a ready made high pressure piston and cylinder with a syringe which cost about 10c each and hydraulics are much more effective than air pressure as it is positive with no lag from the need to compress first before anything happens. Fluid is heavier than air but you only need about 10 ml of it and you can do away with your air bottle, valve and other gear so weight for weight it is comparable if not slightly lighter overall, size for size a hydraulic ram will produce much more power than a pneumatic ram because once you have a cylinder full of fluid you have 100% positive pressure unlike airwhere you have to force in more and more to get a rise in power both being dependant on the source of pressure of course. To me some jobs on models could be powered by hydraulics instead of servos and you can feed a hydraulic line where you may not even be able to get a snake to go, if you need two wing servos for instance for your ailerons why not a central hydraulic feed to two rams which would fit into the wings much easier requiring much less space and be lighter and also not need wiring looms and such. If an undercarriage leg needs one ram and lot of air to raise it then another to lower it (unless it acts by gravity) you can replace this with one slave cylinder that works under vacuum to raise and compression to lower as it is a sealed system, all we would be doing is copying the full sized practice I suppose,
regards, Terry
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On Tue, 13 Feb 2007 14:48:28 GMT, Terence Lynock (MSW)

It sounds like you are familiar with hydraulics.
You may be able to make it work.
Go for it!
Then let us know how it all turns out.
Two problems that occurred to me after my last post:
1. Won't you need to bleed each line? Seems to me that air in hyrdraulic lines is a bad thing.
2. A leaky fitting is going to make a mess. That doesn't happen with air, although failure of a gear might make a different kind of mess.
Not saying it can't be done. In the google search I did, it showed that there was a commercial hydraulic system on the market circa 1998.
                Marty
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Properly done the whole thing could be kept down to 2 or 3 ounces by using medical syringes, may give it a go on a test rig soon as I have time and see how it works in theory,
regards, Terry
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"One observation is worth 10,000 expert opinions."
Let us know how it turns out!
                Marty
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Jet boys have them - http://www.modelltechnik.at/eindex.htm
Cheers, David
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Nice bit of kit David and proves it works but cant understand why they have a fluid bag and exhaust system when it would work with a closed recirculator system, means using a double acting piston so the fluid under pressure pushes the piston down the tube and the oil behind it which is unpressured back to the sealed tank, when the valve changes it works in reverse and the pressure changes sides etc causing the piston to go up the tube again pushing the unpressured fluid back to the tank. There are a number of ways to do it but what you need is as few joints and seals as possible and keep it simple to keep the weight down, using small bore polypropylene pipe instead of steel or copper and engineering plastics where possible,
regards, Terry
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I have a friend in San Angelo who build a complete hydraulic system (but from scratch) for his 19 sized P51's just to go faster than me. It worked very well :(. He is a machinist. However one word of warning, most medical equipment will not tolerate hydrocarbons very well.
contains

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"Six_O'Clock_High" > wrote

So why use anything but water?
Hydrocarbons are used for heat transfer properties, freezing resistance, and a couple other properties. Water is all that is needed for RC.
--
Jim in NC


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You fellows missed the boat...there WAS a company that made a system called hydrolocks or hydralocks (I think it was) that used brake fluid in the system instead of air. I had a system somewhere, if anyone is still interested, I can dig them up. The idea seemed very logiical when it first came out and I bought a set...never got aound to using it, however, Frank Schwartz
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Hydrlocks used a combination of pneumatic and hydraulic. That allowed the modeler to use existing air control syslems from Rohm, etc and still capitalize on the power of the hydraulics. Their claim to fame was that long and/or heavy landing gear, or gear that really need to stay up in high G maneuvers benefited from the incompressibility of the hydraulic fluid. We used refrigeration oil as the hydraulic fluid because it got along with the o-rings in the then commercially available retract systems, and with the diaphragms in the pneumatic/hydraulic interface cylinders. They worked great. It was not difficult to get all the air out of the hydraulic side of the system by simply manually cycling the gear cylinders and having the hose ends in a jar of the oil. You just kept cycling until no more bubbles appeared.
They did add weight (this was back in the days when most scale or pattern ships were 60 size machines), but it wasn't more than a couple of ounces. It was a small price to pay when compared to flying a round of scale with the gear partially hanging out and eating the resuiltant point loss. They did make a mess if you had an "accident", but usually it didn't matter as the plane was likely a write off anyway.
Modern systems seem to be engineered a little better, making these add ons not required.
My recollections anyhow....

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Hi Jim, I have problems when using water in hypodermic syringes as it doesnt lubricate the piston and causes the rubber seal to grab or stick, you could use a mix of water and washing up liquid which would do the trick otherwise a low viscosity oil like baby oil or sewing machine oil,
regards, Terry
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KY Jelly works well once you get the air out. - Don't ask.
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Good point.
Sewing machine oil would have the hydrocarbons issue, again. Baby oil, perhaps that would be good.
How about mineral spirits? That is not oil based, is it?
--
Jim in NC


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Hi Jim, it would be best to stay away from anything from crude oil origin I think if using plastics in the system, maybe as you say a vegetable or mineral oil would be safest for long term use in a system that may be hard to get at once the airframe is constructed and covered,
regards, Terry
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Hi, I think if you search around salvaging motors and so on from old VCR's and the like and the amount of ready made fittings on the market originally meant for other applications but are adaptable then you can cut the need for machining capability down to a bare minimum, cylinders for instance can be fabricated from K&S brass tube using two lengths one inside the other for strength if needed. Once I have learned the art of actually getting a model off the foor and flying it then putting it down again in the same condition it left in I have a string of plans I want to build from and they will all need retracts, a Spit F22, Fw Ta152, Supermarine Spiteful/Seafang (the ultimate laminar flow winged Spit F24), Hawker Fury/Sea Fury and maybe Bearcat so will experiment on building one-off systems for them from ready made componants or fabricate my own if nothing is available. One legacy from my many years of building scale sailing ship models is a good collection of tools including mini-lathe and lots of other stuff so will keep you posted as to how things progress, my main aim will be to keep it as practical and simple as possible so that it is lightweight and reliable,
best regards, Terry
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