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:

 

image3

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!

 

Separating Wind and Bubble Wheel

I decided to try to separate wind and bubble wheel, connected with a belt, making it possible to

  • have a larger surface area for the wind wheel
  • have the bubble wands dive deeper into the tank, thus hopefully reducing the amount of spilling, while having a larger reservoir of bubble fluid
  • gain mechanical advantage by using different sized pulleys

second_ideaAn obvious problem is the friction of the belt transmission. A gear train would be even worse and would add more wind turbulences. At first I wanted to use a large rubber band for the transmission, but a friend suggested the tension would add too much friction, so I will go for some GT2 tooth belt I still have left in the drawer. I found a collection of parametric pulleys here, creating these two pulleys:

small_pulley large_pulleyThey’re supposed to be fixed on the shaft with an M3 screw and a captured nut. I did the same on my new bubble wheel and wind wheel:

bubble_wheel_2wind_wheel_2Trying to print that larger wind wheel (diameter of 160mm) unfortunately turns out tricky — I don’t know what’s wrong with my design, but both Cura and Slic3r decide to slice incomplete layers, the wings oscillating between their full width and getting to small in the middle, leaving a gap:

slicing-problemI have no idea what causes this, but for sure it is a problem of my design, which I actually liked for the simplicity of OpenSCAD:

linear_extrude(height=wing_height, twist=50) {
  for(rot = [0, 60, 120, 180, 240, 300]) {
    rotate([0,0,rot])
      translate([inner_dia/2-2,-spoke_width/2])
      square([(ring_dia-inner_dia)/2+2, spoke_width]);
  }
}

Well, for now I managed to print one by simply using a higher spoke_width of 2.8mm, but I still wonder what caused this … and even that had a sad ending midprint.

I think I’m frustrated for now, just in time to spend two weeks of vacation in Austria, thoroughly clean that nozzle and then try again …

First steps: the too simple solution

Designing the first version of the wind wheel, with bubble wands directly attached, given my lack of experience with OpenSCAD, was surprisingly simple and took 30-45 minutes. While there are plenty of wind wheels out there to download, nothing seemed to really it and I decided to do a simple linear_extrude, with a twist setting. The result looks nice:

wind_wheel

For the shaft I used 2mm welding wire, one that comes in rods rather than as a roll, which worked fine. I printed a few small rings that could be pressed on the wire, to hold things in place. The whole thing is supposed to be attached to this bubble liquid tank:

bubble_liquid_tank

And so, the same day, my first prototype:

assembled1

Let’s be honest: it does make (a few) bubbles facing a fierce wind but we certainly can get better. Mostly this thing spills a lot of liquid with every little bump on the street. I learnt, that while having the wands directly attached to the wind wheel makes things very simple, my first design has some obvious and serious disadvantages to it:

  1. My printer’s build space will only allow for a certain size (in the case of my Kossel mini up to 170mm diameter, damn I’ll have to win some professional machine in a contest!). This means that the size of my bubble wands has to be substracted from the size that still is available for our wind wheel. If you take a look at the wheel above, it’s easy to estimate that getting rid of the bubble wands would allow me to print a wind wheel with more than double surface.
  2. As a consequence of 1., it’s difficult to reach a wind speed that will steadily overcome the friction the bubble wands meet in the liquid.
  3. As the wind wheel should not dip into the liquid, the height of the tank is limited by the size of the wind wheel.
  4. As a consequence of 1. (short bubble wands!) and 3. we have a very small tank.
  5. The size of the tank is even more problematic because we won’t get any bubbles anymore when the liquid level falls below the point where the bubble ring starts — at that point the soap won’t coat the ring anymore.

Because of 5., the tank stores much too much liquid which will never be used, which is a huge waste: because we can only make bubbles until the liquid level falls under a certain point, the following to tanks would get you the same amount of bubbles, but the first one will store a lot of wasted liquid:

tank-skizze

But not only this is a lot of wasted liquid — it will also contribute to the problem of spilling liquid, because the amount of liquid in a simple tank will add to sloshing. That’s why in my second design of this tank I decided to go for the idea on the right. In addition, I decided to put bulkheads into the upper part of the tank to reduce sloshing effects:

mit-schotten

On the photo you can also see a simple mount for the luggage rack of my bicycle. With this setup I was able to produce a few bubbles, but I had to get pretty fast and it still spilled much.

I now decided to drop this simple design and go for a more complex solution which should solve the problem of overcoming the friction in the bubble liquid as well as spilling and tank size. The idea is to separate the wind wheel from the bubble wand wheel.

Development of a wind driven soap bubble machine for my bicycle

So now I finally have a 3D printer, what do I do with it? Printing out downloaded vases, gifts for children is one thing. Wanting to create my own 3D models I quickly came to the vast field of replacement parts for all the things that can break in a household — cool, yes, but this thing is supposed to stimulate my creativity, not just please my wife.

Volunteering at our local kindergarten’s summer party I spent 2 hours animating kids and playing with soap bubbles, small and giant. A lot of time to get you thinking. Of course there are a lot of soap bubble machines out there, but mostly they are supposed to be driven by electric motors. I imagined a large wind wheel, aligning itself with the wind, but our garden, as well as the kindergarten, are pretty much protected by any wind. It was then when I had the idea of a soap bubble machine mounted to the side of my bicycle’s back part: when cycling, a wind wheel would make a ring of bubble wands rotate, picking up bubble liquid; instead of an electric fan, the relative wind while cycling would blow the bubbles.

Of course, there are some unknowns in this:

  • how much wind do I need to create bubbles? Relative wind on a bicycle also isn’t as “focused” as the air stream created by someone blowing on a bubble wand. And: will too much wind have a negative impact?
  • will the torque of the wind wheel be enough to overcome the resistance of the bubble wands passing the bubble liquid?
  • what’s the right position for this to mount? Obviously not the handlebar as I don’t want to have all the bubbles in my face — but if I mount it somewhere behind me on the side, will there be enough wind or too many turbulences?
  • how can I keep the bubble liquid from spilling on a rough ride?

A 3D printer is perfect for this kind of fun project for several reasons: of course, creating a custom bubble wand wheel would be much more difficult without it. But there’s another reason: with a 3D printer it’s much easier to just take a plunge into this problem, just trying out things instead of spending days and weeks on meticulous calculations of air flow, friction etc. You just design something, print it out and see if it works. Then you try again, and again, and again.

My first try was promising enough so I decided to continue:

1. First Steps: The Too Simple Solution

2. Separating Wind and Bubble Wheel