Bubble Machine


The Genesis of the Idea

May 20, 2010

I got the idea of this the old-fashion way: by stealing it. A local brewery, Lake Front Brewery, has a fish fry every Friday night. Along with that they have regular three-piece Polka band that shows up. The band has a vintage Lawrence Welk bubble machine. Whenever the band turned it all the kids flock to the mass of bubbles like insects to a bug zapper. I took a quick look at it and it didn't seem like it would be too hard to replicate.










Safety First

From the beginning my primary directive was to build a bubble machine that did not have a high risk of electrical shock. My plan was to stick to less than 20VDC inside the box. Also I used a galvanically isolated AC/DC supply (and old laptop supply) that was rated at 2x the current I needed. The negative supply was also earth grounded.


The Motor

Previously I had brought home a 24VDC motor with a high ratio gearbox on it from work (No I didn't steal it, I had a proper scrap ticket). My original plan for this motor was to power my rotisserie skewer on the grill. The speed of the shaft was still a bit high for cooking chickens safely so I re-targeted it to power the bubble machine.






The Bubble Disc

All the bubble making devices I have ever encountered were simple O-shaped pieces of plastic. So for the disc I scoured the house looking for suitable candidates. I found an old plastic tray cover that we never used in the pantry. After digging up my 1" inch hole saw and tin snips I had a workable bubble disc.






Air Power

As for fans to blow the bubbles I had lots of fans laying around the workshop. The power supply I selected was 20VDC so I picked to 24V fans.








Bubble Solution Tray

On of my goals was to build the bubble machine out of stuff I just had laying around (i.e. keep it cheap). The one item I was having trouble home sourcing was the tray to hold the bubble water solution. It needed to be long, narrow and at least three or so inches deep to completely cover the holes on the bubble disc. After taking a look around the house and finding nothing suitable I headed to the grocery store to hopefully find a nice piece of Tupperware. Along the way I pasted the juice section. The more I thought about it the more I figured it would be easier to find a juice bottle and modify it. Plus the kids could help me the drink the juice.


Assembly


Case to Put it All In

As for the box to assemble all the parts my primary requirement was that it be plastic so it was easy to drill all the holes in. I had an old plastic file box I was using for spare and broken flashlight parts. I moved the parts to a cardboard box and started drilling holes in to the file box.

Mechanical

I really had no grand plan as far as how it all went together. I started chopping holes and fastening things together. I made a small platform out of 2x4s for the motor to rest on so it would be elevated from the bubble tray. I happen to have some finger safe covers for the fans to keep toddler fingers from being mangled. A few drywall screws and 6-32 bolts were used to hold it all together.

Wiring

The DC power supply I was planning on using was rated at 2.5 Amps. Before wiring it all together I did a quick test of how much current the motor drew and it came in at roughly 0.2 amps. The fans were rated at 0.45Amps each at 24 Volts. Assuming the fans would draw less current when they were under-volted to 20VDC the total load came in at less than an Amp. That seemed reasonable for the supply.

I didn't add an on-off switch. I figured simply plugging in and unplugging would work. I soldered the wires together so they would not loosen up and then covered them with tap to keep any accidental bubble water out.


Bubble Ammunition

Make Your Own Bubbles

I didn't have any bubble solution around the house so I scoured the web for home bubble formulas. I found two quick sources (recipe 1 and recipe 2) that recommended roughly the same formula:
  • 1 cup water
  • 4 tablespoons dish soap
  • 1 tablespoon light Karo syrup

I made a quadruple batch of the recipe and it was enough to fill up the bubble machine tray.

Commercial Bubbles

The second time I fired up the bubble machine I filled it with commercial bubble formula I picked up at a store. It was a bit pricey at $5 per quart but I really didn't shop around. I think you can get a 1/2 gallon for $3 at Target. The commercial seemed to work alot better then my homemade bubble solution. I think I cheated too much on the amount of dish soap I put in my homemade batch so it was probably too watery.

Results

Initial Adjustment

On the first attempt I noticed the bubbles were being blown as soon as the holes came out of the soap tray. The problem with that was the bubble would be blow right into the wall of the case instead of the large opening they were supposed to be exiting through. My quick fix was a plastic fin over the bubble tray so the air would not hit the disc until the disc holes were in front of the case opening. The fin is the blue thing in the box in the picture below.









Airflow Tuning

After the initial adjustment I noticed immediately that the contraption had a bit too much airflow. Small bubbles would go zinging out rather quickly for about three feet in front of the machine. The kids seemed to love that but I wanted some bigger bubbles. What I found was that as soon as I opened the top of the case (less air pressure) the bubbles came out much slower and were much larger. Plus the kids had fun changing the size of the bubbles by opening and shutting the case.

As a second measure of airflow tuning I tried putting the fans in series, effectively under-volting to less than half their rated voltage (from 24VDC rated down to 10VDC). The fans didn't even start turning. So I removed the tape I was using to seal the hole around the motor. That allowed enough air to escape that the bubbles were not firing out too quickly




Bubble Solution Reservoir Shaping

I noticed that there was a large empty space in my bubble solution tank (the modified juice bottle) that really wasn't useful. I bolted in a block of wood to take up some of that empty space so I would get more bubble time out of the same volume of solution.





Bubble Formula

The second time I fired up the bubble machine I used some commercial bubble formula I picked up at a store. The results were much more impressive than with my homemade formula. With the homemade stuff I think I skimped too much on the dish soap. At any rate with the above adjustments and commercial bubble formula the machine was cranking out ridiculous amount of bubbles.








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