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I'd like to be able to blow a constant stream of air for up to two minutes. The purpose of this blowing element would be to play a harmonica, using holes punched in a roll of paper/film to expose certain notes. The film will be mechanically propelled in one direction by a motor.

Would pneumatic pieces be required? (I have had a very limited experience with pneumatics)

Key Points:

  • I would prefer to use as few non-LEGO pieces as possible.
  • The blowing element must be able to reach all notes 1-10 evenly. Each hole in the harmonica is 5x5mm with 2mm in between each note for a total width of 68mm lengthwise.
  • The sound created by the blowing device must not exceed the sound produced by the harmonica.
  • Optional Bonus: The device can also be adjusted to suck air to create a different sounding note.
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As stated it sounds like your intent would be to produce all of the notes at once, but I'm guessing you actually intend to control which notes you want to produce individually? –  Nathan Stohlmann Jan 18 '12 at 16:19
    
@NathanStohlmann: Yes. I intend to blow air across all notes whilst having a piece of film cover most of the notes. It seems more efficient then having a motor go back and forth blowing each note individually. –  Ambo100 Jan 18 '12 at 16:27
    
That does make some sense, though I've got an alternative in my answer. –  Nathan Stohlmann Jan 18 '12 at 16:34
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4 Answers

I think whether the official pneumatics parts would work for this project would depend on how much force and pressure is required to sound the particular harmonica that you are considering. I did find someone who has figured out what the pumps are capable of producing however I can't seem to find a reference for what the tubing systems are capable of supporting.

As a previous answer mentioned, an LA would be unlikely to be able to change notes fast enough so it would be much simpler to put a tubing endpoint at each one of the holes and then control which are active using switches and toggles. However if you do plan on powering multiple end points (which I understand is pretty common in typical harmonica playing) you'll have to think about whether you'll be able to supply enough pressure for all of the notes at the same time or not, and may require multiple compressors.

I would think that the design would end up being something like an M motor based compressor connected to one or more air tanks feeding a manifold with enough outputs for each harmonica hole and then adding a switch inline on each of those outputs.

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You might consider building a Centrifugal fan; they are capable of creating pressure. I built one once and was surprised by how well it worked for moving air, and that was with only 6 radial blades that were 8 or maybe 10 studs wide. Using standard slopes and studs-up construction worked well enough, though a smoother interior would likely improve the results. I think mine was roughly about a foot tall... less than a cubit anyway.

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I like this solution the most as a I can blow air evenly up to 7cm wides. My only problem is the technical aspect of building such a device, like making the housing reasonably airtight and circular. –  Ambo100 Jan 20 '12 at 13:41
    
I think you'll find that studs-up construction for the housing will give you enough air-tightness. My concern would be if you could get enough pressure from it... I'm not sure how much it would take. You might try experimenting with a hair dryer, shop-vac, and small fans and the like to see just how much air you'll need. Building a squirrel-cage fan is a fun little project all on its own, too! :) –  retracile Jan 20 '12 at 14:54
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The pneumatic compressor (I believe it's [partlink:x191c01]) can be used with a motor to produce a continuous stream of air for as long as your batteries last.

You'd still need to find a way to either move the hose or direct air through different paths - as was shown in the points question, linear actuators could be used to move the hoses with precision, however they may not be fast enough to play the harmonica:

Small Actuator

However, if you are looking for a more manual process you could use [partlink:4694b] Pneumatic Switch which allows you to direct air flow through one or other of the two holes, with air being provided to the lower, central input.

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Using linear actuators would require a processor of some sorts to follow a program like a NXT brick. I'm looking for a more mechanical solution. –  Ambo100 Jan 18 '12 at 16:41
    
@Ambo100 by "a more mechanical solution" do you mean that you're happy to toggle switches, or that you want to build the equivalent of a music-box cylinder? –  Zhaph - Ben Duguid Jan 18 '12 at 17:19
    
I'm not quite sure what you had in mind by 'toggle switches' –  Ambo100 Jan 19 '12 at 16:57
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How about a varient of Sariel's Rocking Compressor, (YouTube) and extend it as nessecary to provide the amount of outflow as needed. You could chain a few air tanks togteher as well which may store enough air for two minutes's worth of pressure.

I do not know how much air pressure is needed to make a note from a harmonica, are you sure it could be done with Lego? Also, if Pnueumatics were used you'd have to find a way of sealing against leakage, such as attaching hoses to the harmonica using Blu-Tack, plasticene or Play-Dough (or other local equivalent).

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If you blow hard enough you can play a note from about 2-3cm's away. That would only blow a bunch of notes but with the film would be able to block it out. –  Ambo100 Jan 18 '12 at 16:37
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