empty toothpaste tubes for air bladders ?

I have seen air muscles made out of the neoprene surgical tubing inside a fine mesh/netting material. A prof at Arizona State University was using them for prosthetic development.

Bob

--Festo Pneumatics makes these sort of things but I gotta say they're energy-intensive, expensive and provide very little movement. Maybe it's better to keep working on something that's not off-the-shelf. What's your application? The toothpast tube idea sounds innnnnteresting!

Yeah - that's the idea I have, as well. Although I must admint that for now it is a *very vague* idea ! JCD

anything like that ?

Are you deliberately wanting trash? If not, perhaps a dollar-store could be a cheap source of actuators.

The air-pump water rockets have air pumps that might be hackable into pneumatic pistons. Also, balloon pumps. I've seen halloween haunted house makers write article's on making your own pistons from PVC pipe.

Printer ink refill kits have a plastic bellows device to hold the replacement ink.

I've always wanted to make something that used dryer vent hose as an actuator. It is available in various sizes, but the smallest I've seen in 3" diameter. 4" and 6" are more common....

Well, now you've got me thinking about this again, and I feel the need to elaborate;

The idea is a pneumatic giant octopus tentacle. Take 3 of the dryer vent hoses, and place them around a core made from plastic pool vacuum hose. The 3 vent hoses around the perimeter should be about twice the length of the core. Fasten the outer hoses by either wrapping with wire or tape.

As air is pumped in, or sucked out of one or the other of the 3 outer hoses, the arm will respond by curling.

The air source would need to be something like a shop vacuum. However, I've also considered making a giant joystick by cutting a 30" diameter disk of 1/2" plywood. Put a 6" long piece of 2x2 wood in the center to act as a pivot. PUt a longer stick on the center going up to act as a handle. Then place 3 pieces of 12" diameter vent hose, perhaps 12" long each, under the plywood in 3 spots around the perimeter. As you stand on the disk, you shift your weight from side-to-side and cause the bellows underneath to push out or suck in air which you can pipe to the tentacle.

For further refinement, you might use that hose down the center to pump in air that gets used on another set of vent hoses further down the tentacle. Then, where the 2nd stage gets used, you would need 3 butterfly valves (presumably actuated by R/C type servos) to control the air flow into the end of the tentacle.

Part of the purpose of the vacuum hose down the center is to prevent the tentacle from twisting. But, it may also be possible to omit it. Then it would be possible to extend or contract the entire length of the tentacle by blowing in or sucking out from all 3 chambers at the same time.

Please let me know if you try this idea!

Joe Dunfee

anything like that ?

Naaaaaw. I just like to see how I can recycle things. I was thinking along the line of 2 toothpaste tubes connected with plastic hose. One is inflated and the other is deflated. To actuate the empty one it would be squeezed with a accentrically mounted cyclinder or something like that. When the other one inflates it pushes apart some gripper fingers; shortens a "bicep"; or whatever.

After considering all of that, I started questioning when would it even be worth using air/hydraulic actuators versus electrical. The more I think about it, the more I can not come up with a decent reason. Anyone else ?

JCD

Bad idea. They'd wear out too fast. Sections of bicycle inner tube, though...

John Nagle

Some guy named McKibben will be happy (is he still alive?).

If you can afford to use precompressed air (e.g. cartridges for bb/paintball guns), then pneumatics can beat electrical. I built a CO2-powered car that outraced the competition in a robotics course... also annoyed the professor.

If you first need an actuator to compress the air, then its a harder sale.

Pneumatics are naturally springy and compliant, and they can store energy for quick bursts. Both effects might also be achieved with traditional spring-damper systems, but pneumatics might provide a better shape or actuation profile than a normal mechanical system.

Like hydraulics, pneumatics allow for isolation of the (heavy) compressor from the (light) actuator.

There is a possible energetic advantage of using a storage tank; generally leaving the compressor off, and only running it at the optimal level. However this is offset by leakage and friction in the valves and actuators.

- Daniel

Why would they wear out faster than inner tube ?

Toothpaste tubes are made of thin metal, just strong enough to be filled up at the factory and emptied out by hand one time. Repeated filling and emptying, even with air, would quickly cause it to fail due to metal fatique.

Using an nner tube sounds like a good idea. Speaking of which, I'd like to find an automotive tire inner tube (excellent for making a very-low-vibration platform), but it appears they quit making those many years ago when tubeless tires became common.

Erm, maybe in the 20th century, but mine are made of some sort of plastic.

Oh, geez. Maybe I don't brush my teeth often enough.

You still see the occasional person floating down a river with their head and shoulders stuck through an inner tube, so they must still be manufactured (although it is possible that they are now manufactured only for recreational use).

I suppose I could ask the ballbot guy, it looks like one in this video: