RubensTube
From Simreal
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Ruben's Tube-based Fire Tube
Allrighty then -- the Ruben's Tube is a physics demo that shows the standing pressure waves caused by an audio signal in a flammable gas via the height of the flames along a cylinder. There is a great video of an actual Ruben's Tube on YouTube, here:
What I have built here is only inspired by that device. I saw it and thought to myself, "this would make a fascinating music visualizer; but the flames need to be bigger!". Of course, in the process of cranking the tube up to 11, I didn't keep a nice cylindrical tube; and since I'm feeding it music (and not pure tones) I really lost the visualization of the standing wave. Standing wave? We don't need to stinkin' standing waves!
Dancing Fire Tube is Not Ruben's Tube
(in spite of the name; I used Ruben's name in vain, for search hits)
The purpose, though, of this tube is to be NEAT and to have FIRE. I'm getting there. The next generation will include improvements suggested by several people, if they prove to be worthwhile after testing.
Differences from the proper Ruben's Tube include: larger speaker (subwoofer with a long throw) to push more gas; tighter coupling of the speaker; breaking the pure cylinder to allow an expansion chamber on one side (a gas reservoir); and larger holes with higher operating pressure and louder music, to make bigger, more dramatic flame action.
Publicity
As I find links, I'll add them here.
Making the Tube
The fire tube itself is made from inexpensive HVAC parts (mostly) as laid out in the pictures below. From right to left there is:
- 6" endcap (only because I could not find a 4" endcap, curses to you, you home improvement mega stores!)
- 6" to 4" adapter
- 5' by 4" cylinder (sprung; you have to assemble these)
- 4" to 6" adapter (note the gender differences here; I had to visit two stores to be able to find both types)
- 6" to 8" adapter
- 2' by 8" tube (about two feet; it started life much longer, but I cut it down)
- 8" end cap, to be turned into a speaker mount
- 8" subwoofer (Pyle, in this case; inexpensive and pretty, with a long throw).
Also, below the tube proper, and in the next picture, are the gas fittings:
- Some kind of compression nut (fits the coupler, below; is hollow so gas can get out)
- Nylon washer to help seal the connection inside the tube. It's flexible, so can bend in the tube.
- Brass washer (goes outside the tube)
- Male to Male coupler (1/4" PT, I believe)
- Quick-release gas fitting, suited for Propane. Normal pneumatic tubes are dissolved by Propane (or so I hear), so be sure you get tubing that can survive. I got this one at The Cajun Shoppe
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The construction of the tube is almost embarassingly simple, though I did have to put a fair amount of thought into the speaker mount. How _do_ you attach a speaker to a thin metal tube? Here's what I did:
First, I decided to mount the speaker to an end cap; easy enough decision.
Then I marked on the end cap where all the holes on the speaker were. Fortunately for me, they fit.. barely. I then marked a circle inside the series of holes; the circle has to be small enough (giving enough rim metal) to support for the bolts that will go through the holes, and small enough (giving enough of a center space) to clear the protruding parts of the speaker itself. Note the two lines; the small circle is where I cut to, the larger circle is where I bend the openeing to make it smooth and nice. Drill the bolt holes to the size of the bolts (with a bit of slack, to allow for fit) and a larger hole near the edge of the circle as a starting point to cut out the center area.
I used monster tin snips to cut out the center area, in a large spiral, working my way close to the lines. There is probably an easier way.
Using a pair of slip-jaw pliers, I then bent the ragged, sharp edge of the metal inwards (away from the speaker). This, and the next step where I burnish the edge with the shaft of a giant screwdriver, are to keep sharp bits from the mount from shredding the soft bits of my speaker or the membrane that I put over the speaker to protect it from the propane.
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The mounting ring fits right over the speaker, and the holes even line up, mostly!
The final mounting can occur at any time. To do this, I drape two layers of heavy-duty plastic wrap (cling-film to some of you) across the speaker, pressing it into a form fit to the cone itself. Be sure the film is wide enough to go across all of the bolt holes. Take a silicon caulk and place a bead all around the mounting frame where it will meet the speaker. Taking care to align the bolt holes (I put alignment marks on the edge of the speaker and the frame before starting) press the sticky frame onto the film over the speaker. Now press bolts through the frame - film - speaker and bolt it all together. As a last step, apply more caulk inside the frame, covering the bolts and any holes you didn't use (I only bolted through every other hole). Set aside for a day to dry.
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The two tubes need to be assembled now. They just snap together! Okay, not "just" snap... it takes a lot of wrestling to get them together. First, though, run a bead of caulk along one side of the seam; I put it on the female side, but either side is bound to get you as messy as the other. Then, starting at one end, I wrestled the edges together and got the snaps to snap. To do this, I used two tricks; one is a web strap from a tie down, to give me some leverage towards squeezing the tube shut. I wrapped the webbing around the tube, with one end dangling to the floor (where I stepped on it). I could then twine the upward end of the web in my fist, lifting it up to squeeze the tube shut.
The other trick was to use hose clamps to finish the locking process. Lock one clamp together at the first snap, and then slide a loose clamp up the tube to where I'm trying to lock together some more bits of edge. The miracle of the ramp (e.g. the screw closure on the clamp) then applies massive squeezing force on the tube to force the edges together.
Once built, there is one large hole to drill in the short fat section, and a zillion small holes to drill in the long skinny section. The fat hole is the gas inlet, and is sized to just fit the coupler. The other holes are gas outlets, and their total surface area is the area the gas escapes from. The relative measures of the gas pressure and inlet volume against the size of the outlets determines the height and behavior of the flames. Don't ask me for details, though; I'm just winging this.
I alternate small holes (3/32 or so?) and larger holes (ummm, 3/16 or so?) at 1/2" intervals because, after some experimentation, this proved to be a good combination. The larger holes provide for a bigger, taller, flame; but too many large holes will hurt my gas pressure in the tube, so they need to be farther apart; say an inch apart. However, large holes that far apart don't light very easily; it is vital that the flame be able to travel up the tube to relight the gas jets as they blow out. So the little holes between the big holes help with relighting.
Of course, before drilling all the holes, you'll want to caulk the living daylights out of all the fittings and adapters. HVAC parts leak terribly, and when they are leaking flammable gas, this can be a problem. Drill your holes while these are drying.
The gas inlet is simply bolted into the fat tube, using caulk to help seal it. The fat tube acts as a handy expansion chamber, and holds a large store of pure propane. I found that this helps keep the fire lit during vigorous activity in the music, reducing the impact of air getting sucked into the tube. But only a little bit. There will be more experiments soon to improve flame retention.
Using lots and lots of silicon caulk (I got stuff that was rated to 400 degrees, so it could take the heat), glue all the bits together.
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Video of the Tube
You can see the first prototype in action here (no audio, sorry):
Model 1, detailed above, can be seen here. Differences from the prototype include the large expansion chamber, and I moved the gas inlet from the far end of the tube to over next to the speaker.
New Experiments
In early July, my son Nik and I did a test of the fire-tube with a modification; we sliced the gas chamber off with a hacksaw (which _sucked_; the next ones we hacked off with the bandsaw; no blood spilled! yay!), built and glued in a one-way valve made out of spare sheet metal and an overhead transparency, and then glued and clamped it all together.
The one-way valve made the flames not blow out, at all. I pounded low frequency tone through it endlessly, and still, full flame.
A week later we did the final test; we hacked off the other end, hacked off another expansion chamber, and frankensteined it all together so that we had a two-audio-drive, two-gas-feed, uber fire tube.
Then we put two tanks on it and two channels of sound and... FIRE!
The flames were huge; twice as big as before, which makes sense; and they showed no indication of blowing out under some severe musical input.
I think the final fire tube (Mk 5 or 6) will be able to be run by anyone, without having to babysit it and ride the controls. I'll add in remote ignition, some other fancy features, and it will be very awesome. Also, gonna make it out of much heavier materials, so it won't warp and bend like these have.
Anyway, here's the video that Nik took of it:
(Mark III was not recorded)
One thing I noticed in the disassembly was that the cling wrap that protects the speakers had heated up enough to shrink tight; which almost certainly reduces the effectiveness of the audio driving the tube.
Later versions will have heat-proof silicon barriers and valves, for robust operation.
Mark V Debut
I ran the newest version at Dorkbot on 13 September 207 and it performed well and held up fine. No inappropriate fire anywhere, and it had good flame response to music.
Did some experimentation, prompted by Paul Sicard who was a very good minion at the event, with propane flow -- turning the propane flow down a bit made the flames MORE responsive to the music, though they are a tad smaller in that case.
I may have to make and test a second fire tube (it's modular! I just have to drill a hundred-some holes and snap it in!) with larger holes to see if I can get better response with higher propane flow that way (with less back pressure).
A couple of cell-phone snaps are on Flickr for now:
