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sanddrag
12-05-2005, 07:04 PM
Does anyone know of any places to get miniature hydraulic cylinders (like maybe in the range of 1/4" - 3/8" bore) ? Or, if not, can a small pneumatic cylinder be used for a low pressure hydraulic cylinder? Thanks.

greencactus3
12-05-2005, 09:45 PM
wherever you can find syringes.. multiple bore sizes, multiple stroke sizes, well no needle, just stick a tube over instead.... well a push return is gonna be hard... gonna have to either do an elastic return or find a way to "suck" the fluid out.

ebmonon36
12-05-2005, 10:00 PM
Have you looked into model airplane retractable landing gear? Some of these systems use small pneumatic cylinders that might suit your needs.
Eric

kjhobin
12-06-2005, 06:19 AM
if you need really small pneumatic cylinders you could try some of IFI's Vex products

http://www.vexlabs.com

-Keith

sanddrag
12-06-2005, 12:08 PM
I know I posted in the pneumatic forum but I am looking for small hydraulics. If such a thing cannot be found, I do know where I can get small pneumatics.

However, I cannot use pneumatics because without some fancy tricks they are very fast and only two position. I need them to be rather slow and infinitely multiple position (like hydraulics).

If anyone knows if a pneumatic cylinder can be run with hydraulic oil, please let me know. I was afraid it might eat the seals or something.

It is for a steering setup on a 1:6th scale RC truck.

Now, I had another idea. Could I use a standard RC car oil filled shock, fill the holes in the shock piston (or make a piston without holes) and drill and tap a couple holes in the shock body for fittings? Or would the hydraulic oil get past the piston too easily and cause problems? (or would it eat the plastic piston?)

greencactus3
12-06-2005, 03:41 PM
i have no idea how edible the plastics are to the hydraulic fluid,, but i think rc shocks let out too much between the disk and shock body wall.
how about the lego ones? unless the plastic gets eaten, i think itll be fine with fluids. its fine with water i knwo that much. with air and nonofficial LEGO tubes, it holds air up to 60psi ish.. that i experimented myself... get some TIGHT fitting tubes or find a way to clamp it on... although for an rc truck it might be too fragile.... and slow... unless you widened the stock holes

CraigHickman
12-06-2005, 11:44 PM
The use of a shock piston would not work, because of the holes present inside the cylinder. While in pneumatics or hydraulics there is a seal between the two chanbers, there are small holes in a shock absorber.

sanddrag
12-06-2005, 11:58 PM
The use of a shock piston would not work, because of the holes present inside the cylinder. While in pneumatics or hydraulics there is a seal between the two chanbers, there are small holes in a shock absorber.
Could I use a standard RC car oil filled shock, fill the holes in the shock piston (or make a piston without holes)... :)

Tristan Lall
12-07-2005, 12:06 AM
What about using a food-grade medium, like glycerine? That would very likely be safe for the seals in a standard aluminum & stainless piston. Or to be absolutely sure, use it with a food-grade piston, with nylon or delrin end caps and stainless body; those seals have to be especially nonreactive.

Cuog
12-07-2005, 12:31 PM
you could always find out what the seal in pneumatics is made of then see if the material is "edible" by the fluid

TimCraig
12-08-2005, 01:44 AM
Does anyone know of any places to get miniature hydraulic cylinders (like maybe in the range of 1/4" - 3/8" bore) ?

This company has cylinders down to 3/8".

http://www.cylval.com/cylinder.htm

Mr.G
12-08-2005, 04:59 AM
Isn't small and hydraulics an oxymoron.

I work in a plant that has a lot of machinery with hydraulic to build engines, and every thing is big. Most hydraulic cylinders are rated for at least 3000 psi and up. In order to hold 3000 psi the cylinder wall has to be thick.

You are also working with a fluid that is not as safe as air. If the system developed a leak, (and yes they do - i think hydraulics and leak are next to each other in the dictionary) and the leak was in the form of a stream of fluid it can easily at 3000 psi get under the skin and be fatal. Not only that, with fluid spraying everywhere it can easily get in your eyes. We have systems with 10's of thousands of gallons of hydraulic fluid and pump that don't stop or run out of fluid. In the past few years we have had people make a mistake and had thousands of gallons on the floor and a soaked employee(there is no hiding that one - it like a terrorist making a bomb and having it exploding). Most of the time people think they shut everything down and they shut off the wrong part and then they try to remove a valve.

Mr.G
12-08-2005, 05:23 AM
In your investigations you may want to consider a thing called "air over oil". This way you don't need a hydraulic pump and all the other equipment. If you already have pneumatics on whatever you are building and only need 1 or 2 motions then air-over-oil may sound like the better option.

Here are some animations

In this one the cylinder on the left could be a pneumatic cylinder with air on top, or a pressure reservoir with air pressing directly on the fluid.
http://travel.howstuffworks.com/animation31.htm

Here is another variant.
http://www.airhydraulics.com/Products/CSeriesAirHydraulicPresses/Animation.htm

Gdeaver
12-08-2005, 09:54 AM
Brake cylinders are kind of small and the junk yard is full of them.