Yes, it works!

Well, not that much to say, only that it’s pretty hard to capture this in its real beauty — for some reason unknown to me, photos will always be taken in the wrong moment. But, then again, who cares:

 

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For now, just a bad short video with the mobile phone, but enough to upload it to YouTube for now:

Another one is printing right now — the kids have been asking!

 

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Maybe it works!

This is so exciting! I put everything together today and, while there is still a way to go, now I definitely have a feeling like this is going to work. My first machine!

Assembling it I soon noticed small things which I could quickly address by printing new parts — mainly the bubble ring needing sufficient clearance on both sides, so I printed small spacers.

I decided to go for rubber bands instead of GT2 tooth belt, because I had no idea of how to glue a tooth belt to a continuous loop of a certain length, and, well, I want to publish this and a GT2 tooth belt isn’t exactly someone people have at home normally. Common broad rubber bands like we use them at office for large acts have a too small diameter. So I used elastic ribbon, the kind you have in your underwear. I used needle and thread to make a continuous loop; you have to take care that it’s just tight enough to have enough friction on the pulleys, but loose enough so you don’t have too much friction by skewing the axis. Well, it does work and it looks fantastic — when I have one on either side and the wood painted black as well, this will surely remind people of a jet engine! Well, maybe, at least:

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Well, it works sort of. Problems remaining:

  • I need black elastic ribbon!
  • the large pulley behind the bubble wheel is so large that it pops most of the bubbles; I’m currently printing a smaller one, but if it get’s too small, my mechanical advantage might get too small, too. We’ll see in, let me see, 13 minutes!
  • the belt retainers on the pulley are too small for my rubber band, which keeps getting of after a short time, but I already accounted for that with the pulley printing just now;
  • my tank is not completely water-proof; it’s okay for now, but it get’s soapy on the outside. I’ll try making the walls a little stronger and with more infill for the next tank.

Aaaah. This feels very good.

The bubble fluid tank

Ok, contest deadline pressing I did the tank today. While the code is certainly chaos by now, I really love OpenSCAD: if you’re reasonably fast with typing, you can model quite fast, you have a very natural, easy way of accounting for certain constraints, and it’s fun. While of course a good OpenSCAD design should be fully parametric, allowing to easily scale my design to any wheel diameter, this is in reality not always easy to achieve, however. The tank I came up with still takes some modifications if you scale parameters by more than a bit, but hey, it’s my first machine!

Ok, so here’s the tank, fit with a mount to screw it onto a piece of wood which is supposed to be mounted on the back of your bike:

tank

This takes some important things into consideration: the largest part of the tank should be only above the lowest bubble ring, to save on bubble fluid. And, to reduce spilling, I inserted bulkheads (which also serve as internal supports during printing), as well as a small wall in the upper part that also tries to reduce spilling. Here’s a cut to show how it looks inside:

tank-cutAbove the bulkhead walls you can see small holes supposed to let air circulate, so you don’t get problems with enclosed air when filling this with bubble fluid. Of course, a cap to close that refilling hole still has to be printed.

This has to be printed reversed, i.e. with the top down. It will still need support under that mount and probably in the middle of the half circle. There should be no support in the tank itself (except from above that refilling hole), as you won’t be able to remove it easily, and it won’t be needed because of the bulkhead walls — so I let the slicer generate support only from printbed. Although the first layer has a very large surface, I could get the first layers to print correctly until I turned on a raft; this is probably due to poor calibration of my printer.

This thing has now been printing for more than 4 hours, which is longer than my printer has done ever — it hasn’t even printed half of it, though. We’ll see. It’ll be a pain after this, when I’ll find out this doesn’t work …

Slowly getting somewhere …

Back from a long summer vacation I finally got back into working on this, with the deadline for the thingiverse windcraft tech challenge pressing me. The good news: I’ve finally found the design fault that made the wind wheel so problematic while slicing — the rendering quality of the linear_extrude command with tilt=50 greatly increases by not only increasing the number of facets ($fn=50) but also using the „slice“ parameter. While I have absolutely no idea what this parameter does exactly, neither do the authors of the OpenSCAD Manual, where it simply states: „The slices parameter can be used to improve the output.“ Well, setting slices=100 did it for me, so while not precise, the manual is obviously right. Because theres only a thin surface touching the bed, a raft is in order. Also I increased the brim surrounding the wings, to give it more stability during printing. The result is this:

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On another note, I found someone aiming for something similar as I do — a wind bubble machine, published on thingiverse on July 1st, shortly before my vacation. It looks cool and the idea with the gear design is charming; I’ll try it out when I have time, but won’t bother now as it will be quite some printing and I did not find yet any fotos or videos of it working under real conditions. As of now, I will not go for such an, admittedly beautiful, design, for the following reasons:

  • I found out by now, that the resistance of the fluid actually is a problem, and this will probably increase with the teeth of the gear going through the liquid; this may be neglectable because of the mechanical advantage of the gears, but I would like to go without
  • with the bubble rings being inside the gear, you have less room where the bubble fluid is actually effective, so you have to refill more often
  • while having the fan mostly in front of the machine gives a compact overall footprint, it shields a lot of the travelling way of the bubble wheels, probably reducing the amount of bubbles produced during one turn of the wheel
  • the tank is not done with bicycle usage in mind and will definitely spill its liquid after a few meters on the street; so it may be fine for the garden, but not for my purposes

So I’ll continue with my tooth belt approach. As most people don’t have tooth belts at hand, I will also evaluate a rubber band or similar things.