The fabric is rip-stop nylon, that I found in many colors at the local Joann store but you can also
buy online for just
$8 $5.60 per linear yard, 59" wide (I bet it is great to make kites).
The top is made by a series of truncated cones and cylinders, plus a flat top, but with pressure the edges become rounded, what in this case was nice. If you cut a cylinder and lay it flat it becomes a rectangle. A cone lays flat as a sector of a circle. To calculate the dimensions of the panels you only need to draw the profile and at each change of slope (corresponding to a seam) write down the distance from the axis and the height. A couple of equations gives you the radiuses and lengths of the arcs you have to draw. This top has two vertical seams, so each section (except the top and bottom) is made of two panels. They get pretty big fast, and arcs can have centers far outside the fabric. So I had the fabric taped to the floor, a string tied on one end to a heavy base that acted as a center and I was on my knees marking the circles with a fabric pencil. I cut the panels leaving half an inch edge for sewing.
So, you made that inflatable all by yourself? Very nice.
Actually, Beatriz joined the panels with a sewing machine (and some hand stitching), which was a considerable part of the work. She did it on the inside and then pulled the whole thing inside-out through the 4" cylindrical opening at the bottom.
To inflate the top I used a 1/8 HP, 120 CFM blower (XPower BR-2C01A), the smallest commercial blower I could find, that I bought used (new sells for $50 plus shipping through Amazon.) There are some oversize computer fans that could have worked, but I wanted to make sure I had enough air to make it rotate.
The blower feeds a 3.5" pvc pipe that goes into the top to inflate it and serves as the spin axis. Some air is lost there but I wanted a loose fitting to avoid friction.
It was very important that the top rotated. I accomplished that by having two jets of air on opposite sides of the rim:
I made those by overlapping 4 inches of fabric at the seams of the rim band. One end of each of the 5" wide panels widened so it would leave a gap for the air to exit. They blow quite a bit of air. I made sure the jets pushed the top counter-clockwise
Unfortunately, when I first tried this design, it would fold at the neck of the tip and the top would not get vertical. So I first added a 1" pvc pipe at the center to make it stand up. It worked pretty well, specially when I added at the end a big bearing I had. But it made a protuberance at the crown so I tried to make a bigger support. Beatriz did not like the idea of opening the top and sewing it again, so I came up with a tube ring supported by three spokes that I could assemble inside through the 4" opening (like putting a ship inside a bottle):
As you can see on the video it worked very well (it spins at 30+ RPMs).
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Topic: Very big top first spun (teaser) (Read 7431 times)