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[on:]

Hello,

I'm obviously new to the Arduino forum but I've been working with a partner on a project for air muscles, using a solenoid as a switch to inflate and deflate the muscles. I've spent some time looking at the solenoid tutorials on the playground,looked at some previous posts, and have put together a schematic of what I thought our design may need look like. We don't have a solenoid picked out yet but I'd assume a lower voltage of about 12 V would work. Our plan is to use two solenoids to turn two different sets of air muscles on and off.

Because our solenoids will only be able to inflate and deflate the air muscle, we decided to include the compressor in our design. Using the Arduino, we would shut the compressor while the solenoid was open to the air muscle so that the air muscle would technically remain inflated but not taking in any additional air. Because the compressor connects to the wall/main, I realize we need a relay for the connection between the compressor and the Arduino but do we need relays for the two solenoids as well?

Also, if I when using a transistor for solenoids, is a heat sink required? I read in some it does. Is there a good website or book I could reference that anyone is aware of?

If anyone could look at the schematic and let me know what they think, I'd really appreciate it.

Thanks!

[Reply #1 on:]

thunderclops
I do not understand why you want to switch the compressor.
Mostly it is not needed (if your valve is closed the compressor doesn't fill it anymore) and secondly "any good enough compressor to do more than blow up a tire or balloon has a pressurized barrel" which makes switching of the compressor useless as the barrel keeps the pressure high.
Also most compressors remove the pressure from the pump when you switch it off. This is done to make sure you can start the pump.

If I were you I would look at some documentation of air parts providers that serve your region. For instance festo or parker. They mostly have good documentation on parts an technology. Notice however that these parts are mostly hard to get without vat number.
Best regards
Jantje

[Reply #2 on:]

If we close the port that connects the compressor to the air muscle so that the air muscle is deflating using the exhaust port but meanwhile, the compressor is still on, will the compressor build up pressure? Or is that what the pressurized barrel does? Does that pressurized barrel reduce pressure applied if a solenoid is closed and the tubing inside has already reached the established pressure?

My partner and I had a new idea where there be a solenoid that opens to the second set to solenoids(that interface with the air muscles). This first solenoid could have the compressor send to an exhaust valve rather than continuing to build pressure when the second set of solenoids are both closed.

I attached a drawing of the new idea. The red line denotes the air tubing while the black would be the electrical.

[Reply #3 on:]

Your transistors appear to be wired incorrectly. The Arduino outputs should connect to the resistor (to limit current output from the Arduino) and then to the base. The emitter should be connected to ground. Your transistor symbol also shows a darlington pair which isn't at all necessary here.

See the "Using a transistor as a switch" section at http://www.kpsec.freeuk.com/trancirc.htm for a refresher.

With respect to the compressor/tank you should treat the two as a standalone system. Normally this would be controlled by a pressure switch (example) to automatically turn the compressor on and off and keep the tank pressure within a set range (that pressure is adjustable within the switch). The above switch also includes an "unloader" valve to release pressure on the compressor so that the next time it kicks on it gets a chance to get a sort of running start before it goes under load. That's the thing that makes a "PSSSssssh!" noise every time the compressor shuts off

To answer your question, if you keep the compressor running with the valves closed it will continue to try to build pressure until a safety valve pops or the compressor overheats/explodes/etc. If I were you I'd suggest not worrying about procuring a compressor and just make a small tank out of PVC pipe (pressurized to no more than ~20 PSI) and pressurize it with a bicycle tire pump or such. You can buy a valve stem for a car tire to use to fill the tank (just drill a hole in the side and stick it in), and for an outlet you can tap and drill one of the end caps of the tank and thread in a 1/8" or 1/4" NPT fitting which you'll later connect to your solenoids.

[Reply #4 on:]

Oh! Thanks for that fix on the base-emitter labeling(or is the structure wrong as well?).

Unfortunately we're somewhat stuck with the compressor because it was given to us and also because we are becoming pressed for time on the project.

Thank you both for all your help!

[Reply #5 on:]

I also would make something like that.
Where have you buy the air valve ?
And what about the compressor, can i use one like this http://www.ebay.it/itm/MINICOMPRESSORE-MINI-COMPRESSORE-PER-BICI-AUTO-GONFIA-/200590855724?pt=Ricambi_automobili&hash=item2eb4258e2c#ht_9081wt_1037
Let me know.
Valerio.