Pneumatic Cylinder?

[mmcdonald]

Hey all,

I'm not a mechanic and I know nothing of the topic. I am however looking to replace the legs on my computer desk with some electronic cylinders so that I can raise and lower the desk at the press of a button. The only issue is, I don't think it's a pneumatic cylinder that I'm looking for as their bore is quite small as is their stroke. They're also pretty bloody powerful and might launch the monitors in to the ceiling!

What is the name of the component I'm looking for? The description: a cylinder shaped device that extends in a single direction that can operate at the push of a button and can lift some weight (60-80kg would be ideal).

I think you get my drift... this is a small project I've been interested in screwing around with.

Thanks!
Michael

[pritaeas]

You mean like this:

http://www.mockett.com/furniture-legs-casters/electric-legs/tlel3.html

http://www.eastwood.com/blog/eastwood-chatter/pneumatic_table/

[mmcdonald]

Exactly this - though I'm after the name of the internal component. I built my desk myself and it's quite a large set-up. I can't find a ready made frame for this desk and would most likely need to make it myself. Plus it's more fun :D

[mmcdonald]

Right I'm sorry the second link was perfect - looks awesome!

[mike_2000_17]

Generally speaking, the component you are looking for is called a "linear actuator". It is most commonly using pneumatics (compressed air) to get their power, as those shown in the second link by pritaeas. However, you have to understand that with such a system, you need a source of compressed air. In that link, the application revolves around a workbench in a shop, and in such shops, there is usually a source of compressed air available (for pneumatic tools and such). I imagine that the intent with that rig is to manually plug the pneumatic actuators to the source of compressed air (with a hose) whenever the guy wants to raise the workbench. If you wanted to use this in an office environment with no pre-existing source of compressed air, you would have to install one, such as these:

https://www.acklandsgrainger.com/AGIPortalWeb/agi/Pneumatics/Air-Compressors-and-Vacuum-Pumps/Portable-Electric-Air-Compressors/_/N-1vec

And, of course, if you want easy "switch-of-a-button" control on the raising and lowering of the desk, then you'd have to rig up some electronic control unit for it too, to control the valve and the air compressor. Overall, this could end up being quite difficult, expensive, ugly, and bulky.

A better option might be to go for an electric linear actuator. This is a bit less common, given how in industrial environments pneumatic or hydraulic actuators are more practical and cost effective. However, they do exist. They are usually based on a "lead screw" design, which means that you have a geared electric motor that winds a kind of infinite screw up and down. The last time I used such a thing (for building a robot), I used the linear actuators from Haydon-Kirk:

http://www.haydonkerk.com/LinearActuatorProducts/StepperMotorLinearActuators/tabid/66/Default.aspx

But many of the eletric actuators / motors take DC current (usually 24 or 48 Volts), which means you need a transformer to plug it into AC current (120V wall outlet). There are some products that can be hooked up to a standard AC power source (120V / 60Hz), such as these ones:

http://www.thomsonlinear.com/website/com/eng/products/actuators/electrak_5.php

But, of course, that one can take a static load of 2,500 pounds, which is definitely overkill for your application. But if you keep searching for similar products, I'm sure you'll find something that works.

In either case, you should follow a design similar to what was done in the second link given by pritaeas. There needs to be an upper half frame and a lower half frame that have their legs into each other. The point being that linear actuators are not replacements for actual supports (legs), they are just there to push and pull, and take a perfectly straight load (no side loads). This is even more true of electric actuators. To that point, actuators are usually mounted on ball joints or pin joints on both ends (and they often come with ball/pin joints already as their mounting points, such as the Electrak product I linked to). This makes it virtually impossible to use the actuator for anything other than a straight load (it's called a "two-force member" in engineering terms). If you need to buy ball joints, you can just look up any half-decent parts store, like McMaster-Carr, which all have wide assortments of ball joint rod ends.

[HiHe]

Maybe a foot pump will do.