Build notes: Sheet metal working, and pilot lights

I've had a 4x8' sheet of 22ga steel sitting in my garage (leaned up against my hexayurt) for probably about six months now, since starting Mocobe really.  So, it felt good to finally drop it in the back of my pickup truck and haul it over to the shop to start making the sheath for the linear drive unit.  (22ga was the thinnest I could find locally that wasn't galvanized; I was shooting for 25ga, but it wasn't available.)

First things first, I took the rail holders that I had bolted on with some difficulty, and welded them in place.  I can't remember why I thought that bolting them would be necessary; I think I was under the impression that they might need some lateral play, in order to make sure the rails slid on properly at both ends, since they're separated by 8 feet.  That is certainly not the case, the rails fit on fine with the holders welded in place more-or-less-straight.

I also cut a couple of segments of 3/8" pipe (same pipe I was using for bolting together the two 4' segments) and welded on a couple of holders for 1/8" copper refrigeration pipe, to use for pilot lights.  Some photos of the pilot lights below.

These are hooked up to a 1/2 PSI regulator, and have 1/16" holes in them, but they still need a needle valve to dial back the flow rate a lot.  I wrapped these in a small amount of steel wool, but I found that it wasn't effective at preventing simulated blowouts, so I might need more.

Now: On to the fun stuff!

Cutting the sheet metal was a bit of a pain.  There are a lot of options here, but few good ones:

• Band saw: too unwieldy for a piece this large, and too hard to make straight cuts
• Plasma torch: Excellent!  Except that TechShop doesn't have one anymore.  They did years ago, but it broke and they never replaced it.
• Oxy acetylene torch: Too messy for something this thin.  And I don't remember how to use it.
• Water jet: Too expensive for a simple straight cut.

I decided in the end to go old school, and used an angle grinder.  Simple, reliable, and hard to screw up.  I tried a few things, with different cuts, and found that I could make a decent straight cut free-hand, but that using a guide made it a lot easier.  I found a 1.5' piece of steel scrap with a 1/2" 90 degree bend in it that was perfect, and if I keep doing it this way, I'll probably make a longer one.  But, ideally, I'd like to do this with a plasma cutter in the future.  You can use it with an aluminum guide and make quick work of it.

The layout for the sheath was to take a 4' long sheet, and bend it into the sheath of the correct shape, leaving a gap on top for the flame to exit.  Here's the plan:


I can use the finger brake for the first two bends easily.  After bend 2, I leave it in the brake, and make the third bend, on the first 6" segment.  The finger brake only opens about 3/4 of an inch, and after the third bend, it's got 6" vertical behind it, but I can work it out with a bit of effort by pivoting the piece.  But I definitely can't make the last bend this way, as getting it out of the brake would be too difficult.  So, time to go old-school:

The fit isn't perfect, but it's good enough.  I went about drilling some holes and tapping them to hold the sheath in place, and a) spent way too much time using the drill press when a hand drill was just as effective, and b) broke a 6-32 tap.  I have broken several 6-32 taps already on this piece, and I was thinking about why this might be, and came to a realization:

I originally started using the 6-32 tap because, for a particular piece (maybe the stupid rail holders?) I needed as small a bolt as I could reasonably use.  I dumped a bunch of 6-32 bolts into my tool box at some point, and thereafter I just kind of defaulted to using the 6-32 tap for everything.  But, this was incredibly stupid: the 6-32 tap breaks most easily because it's the smallest tap.  I did the second sheath with the 8-32 tap, and it was like butter.  It took me about 50% longer to drill the holes, but less than half the time to tap them, and the tap was way more stable.  So, advice: don't use the 6-32 tap on steel if you don't need to.

Next up: putting it all together.  I'm starting a new job soon, and am hoping to get this prototype done before then, so the next couple of weeks are Flaming Icosahedron time.  Stay tuned.

A Guide to Fire Art Safety and Construction

I wrote an instructable.

Chain drive with pulley wheels

Been hard at work trying to fundamentally transform behavioral therapy lately, so not a lot of time to tinker.  But I took a few hours this weekend and did something I've been meaning to do for a while, which was to update the chain drive mechanism using pulley wheels as guide wheels instead of sprockets (thanks to CTP for suggesting this).  I also made the effort to make sure a few other things were tied down properly.  The resulting mechanism is much smoother and more reliable.

Mechanical drive train prototyping

Pace of development has definitely slowed down, as almost all of my time these days is dedicated to Mocobe, but I was feeling lazy today so we walked down to Balompie #3 and had pupusas for lunch, and then I spent some time in the afternoon tinkering with the drive train.  I've been working on it on the weekends a bit, and instead of building it all in one go, I decided that for something this complex, I was going to try roughing it out first.  This gave me a good opportunity to try a few things out and fix problems as they arose before I settled on a final design, without having to machine a lot of parts and drill a ton of holes in steel.

I used scrap aluminum plate, and did the work in my basement, with an angle grinder to cut the aluminum and a hand drill to drill the holes, which is a lot faster than drilling holes in steel with a drill press.  Fortunately, as well, I have a good sized collection of clamps, so instead of drilling into the frame, I just clamped the pieces onto it, making it easy to adjust them, remove them, and move them around.  To attach the chain to the shuttle, I made a really janky attachment point with duct tape, some wood, and a couple of eye hooks.  Eventually I'll weld an attachment point onto the shuttle, but I wanted to test this out first.

Here's the drive train in action:

Some notes from the build: 

One thing that's different from the previous version is that I added a 15 x 20 mm cable carrier to the hose.

 

It's actually two, bolted together.  The problems I was having with the hose tracking properly are totally solved by this, the hose bends fine and doesn't get tangled in the rails at all.  Since I haven't machined the sheet cladding for the whole thing yet, I hope that it will still work okay when it's constrained.

I had to make a bunch of adjustments as I was getting the drive train to work: the tensioning gear here is critical for holding the chain against the drive gear.  Otherwise the whole thing slips, there's too much play in a chain that long.  It's also really important to get these three gears aligned properly:

Otherwise, it puts a lot of strain on the swivels.  I bought swivel hubs from Servocity for mounting the sprockets (also available at Sparkfun) and found them to be junk.  The free-play of the hubs is bad, and they repeatedly fell apart when they were used under strain.  The halves are simply held together with a nylon lock nut and  a bolt.  Presumably the idea is that the lock nut prevents the bolt from loosening (or tightening!) and the halves will just rotate against the washer, without moving the bolt.  In practice, I found that in use, the hubs either fell apart or seized up due to over-tightening, depending on the direction of rotation.  It's possible that this was due to lateral strain from misalignment of the chain, which caused pressure on the washer.  In the end, I don't care why, they're not robust enough for this application.  I wound up disassembling the ones that were failing and just putting a bolt through one half, and leaving it mostly tightened.  That was fine for the time being.

I'm also thinking that a faster motor would be good.  This is running flat out, and it's got way more torque than it needs.  I'd rather get something faster, and be able to run it at slower speed using the speed controller if I need to.  I bought this one from Servocity, which runs at 118 RPM max speed, but I could just swap it out for the 313 RPM unit and I'm pretty sure the torque will be plenty.

I haven't decided on the design of the chain attachment point for the shuttle, but I'm thinking it might be handy to have some sort of short linear tensioner, like just a screw with 1" travel.  Being able to link the chain on and then screw it down to tighten would make life a lot easier.

Also, it turns out that my bicycle chain breaker doesn't work for this roller chain because the pitch is different, which isn't surprising.  I can try doing it the old fashioned way by just pounding out a rivet, but last time I tried that with a bike chain I smashed a finger.  Or I could just cut it.  I looked for a 0.25 roller chain breaker, and found this one on Amazon, but since it's made by Koch Industries,  I won't be buying it.

Shuttle production model build notes

Hey amigos, I know it's been a while since I've rapped at ya.  I've been working on starting up a thing, which you probably already know, because if you're reading this, you're friends with me.  And if you're not friends with me, and you're reading this: welcome!  I am a handsome and accomplished man!

But, in between hacking together React widgets and swearing at JavaScript for having ever been invented, I put together a new prototype, which I am not thinking of as a prototype, it's really a test-build for a production model.  Here's the goods:

The entire thing is 8 feet long, made of two 4 foot halves.  The framed ends are 6" by 6" 0.120.  1/2" wide on the ends, and 1/4" wide on the parts in the middle.  These are held together with 1/2" square tube, welded onto the frame ends.  The rails are made of 8 foot long segments of 1/2" EMT electrical conduit.

The shuttle is similar in design to the last one, but the rail holders are solid tubes, and much larger diameter.  The 1/2" tube rails are much stiffer, and the rail holders are just welded onto the pipe holder in a single line.

The rails are held to the frame ends by 1/2" metal rod which is welded onto 1/2" wide segments of steel right angle.  These are screwed into the frame ends which are 6-32 tapped.  I broke my tap off in one of the frame ends at one point, and just used a cold chisel to break it off, and moved the hole.  It turns out that these tap extractors don't really work, at least not for a tap that small.

When the motor and chain drive are installed, I'll wrap the whole thing in 22 gauge steel (which is the thinnest I could get from Bay Metals that wasn't galvanized.)

Need to attach a hose and check how the running actually works, then buy and install a chain drive.  But, it's coming along.  The chain drive will be fun.

Working shuttle prototype!

Simplify, simplify...after about a year of prototyping, I finally sent out some feelers and did some networking with some other fire artists, to get some feedback on my designs.  I had a good conversation with DaveX from BMOrg, who made a couple of observations that stimulated a line of thought that I had been rolling around in my head for a while.  I hacked together a prototype out of 6" diameter HVAC conduit and off-the-shelf end-caps.  All the "machining" I had to do with it was to cut a 1" slot freehand with an angle grinder, and I cut some strips from the leftover which I screwed into it to form it back into a rounder shape:

I drilled some holes in the end caps for the rails, and used the end caps from the previous prototype to hold them in place.  Then I threaded the old shuttle onto it.  With just the slot in the top, the effect is nice, but the flame is very concentrated, and it definitely has the aesthetic of something mechanically moving the flame underneath:

BUT...(and this is where DaveX's suggestion comes in), I then fit some aluminum screen over the slot, and laid some steel wool over it to use as a diffuser.  The effect is a much more organic-looking flame:

I think this looks great, and it's incredibly easy to build.  The only welding and machining is of the shuttle.  I have some issues with the hose tracking to work out, and I need to motorize it.  But this is going to be the basic design I'm going to go with for the eventual build.  I may even extend these to 8 feet long, if I'm going to start with a pyramid instead of an icosahedron, just to make it more impressive in scale.

Tomorrow morning, I'm going to start a new venture, starting up a software company.  That may or may not work.  But it is going to take up a lot of my time and my vacation is officially going to be over.  I'm very satisfied that I have a working prototype, and even if my progress slows down, I know I can get this up and running eventually.  Onward, and upward.

Shuttle prototype v5.2: Getting Better All The Time

Spent some time testing the shuttle prototype with various air intake mechanisms, some of which produced better results than others, but none fantastic.  After the intake fan burnout I decided to go with MOAR AIR.

I had two main strategies: air mixing with the gas line, and forced air into the sheath.

My initial gas mixing strategy was to inline a vacuum ejector into the gas intake, but this had no discernable effect on the output flame color or constitution, so I got rid of that quickly; if there were significant enrichment of the flame with air, I would have seen a much bluer flame, due to more efficient burning of the propane.

To test a compressed air source, I tried to build a ghetto fabulous compressor by hooking a really cheap 12V tire compressor to an old propane tank that I had converted into an accumulator:

 This worked a bit, but it took about 30 minutes to pressurize the tank to 40 PSI, and after the third time, the poor little compressor blew a gasket.  So much for plan A.

Plan B was to rent a compressor:

I hooked this up with a T into the gas line, with a check valve at the gas line to make sure the air didn't flow back into the gas line.  The compressor went up to 120 PSI, but the regulator on it wouldn't go above 60 PSI.  This turned out to be plenty though, at least for my initial tests.  Simply mixing the gas with the air, even at 20 PSI, would blow out the flame.  The regulator didn't go much below 20 PSI, so I installed a 1/4" needle valve so I could make fine adjustments to the air flow.  I wasn't able to get any improvement over the usual observations: poor flame, mostly confined to the sheath and blowing out the ends.  This was at low gas and low air flow.  At higher air flow, the flame would blow out, and at higher gas and air flow, it was about the same.

If I removed the shuttle from the sheath and ran the gas at 30 PSI, it produced a great flame.  If I slowly introduced air, I could create a nice blue flame, clearly modulating the air/fuel ratio.  By adjusting it this way, out of the sheath, I was able to ensure that I was getting the right ratio.  But putting the shuttle back in situ, the results were very similar to before, little or no sustained flame.  This suggests to me that the primary issue may not be air mixing, but ineffective ventilation of the exhaust: as soon as the gas starts burning, exhaust builds up in the chamber and snuffs the flame.  I would still expect the gas to burn under these conditions if I'm supplying enough air.  But it's possible that the "correct" ratio that I see with the shuttle in the open air is a result of the introduced air + the atmospheric air, and that in a confined space, the lack of the latter is enough to kill it.  This would suggest that it IS possible to supply enough air with the fuel, possibly.

I next tried an air manifold that inserted along the bottom of the chamber.  I took a 1/2" pipe and drilled 1/4" holes at 10" intervals, 10" from each end (so, 6 holes total).  I machined plates that fit over the fan intake fittings to hold it in place.  This also would help force the introduced air up towards the flame outlets at the top, instead of simply flowing out the open ends.

I ran these at 60 PSI, at pretty high flow rates, and fiddled with the gas to get various effects  Here's what I got at about 30 PSI gas:

The flame isn't very tight, but I'm definitely getting a translation.  At higher PSI, instead of getting a larger flame, it was simply getting spread out further, getting less localized.

I have an idea next to simply improve the ventilation of the sheath by cutting the upper half of the sides off, and seeing if this gives me the desired effect; if it does, then I can possibly reintroduce some shielding by adding sections of 6" diameter HVAC conduit.  The purpose of this is to keep the innards hidden, so that the mechanism isn't obvious.  This is the real issue I'm seeing: if I cut the top off the sheath, this would probably work, but then it would be obvious what the mechanism was, and the aesthetic would kind of be ruined.  So trying to get this to work inside the sheath, or SOME kind of sheath, seems like what I'd like to do.  Possibly going to an even larger sheath, or adding more holes to the top, or all of the above could also help with ventilation and exhaust.  Some progress, but still needs work.