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19 Sep 2007 08:18 UTCWed 19 Sep 2007 - 8:18 am UTC
I asked another question about how to build a truncated icosahedron (a buckyball). See:
However, I've decided that perhaps it would be better to approach this from a different angle.
What is a good geometric shape that I can make which will allow me to make a human hamster ball (a 6 foot diameter ball).
The only problem with a truncated icosahedron is that it wouldn't really roll that well.
Instead, I'd like to start with a hamster wheel shape. See:
and then build out the sides to be a sphere shape. That way it'd actually roll well.
Building a hamster wheel would be easy. One side is just a 90 degree angle for the connections. The other side is the angle of whatever 2D shape is determined by the number of sides of the wheel. I could then put in flat boards and end up with a wheel.
However, how do I go from there to making a ball shape? It wouldn't need to roll along any axis other than the wheel axis.
I'm pretty much looking for instructions on what angles to drill the holes into the balls that would sit at each vertex.
19 Sep 2007 21:22 UTCWed 19 Sep 2007 - 9:22 pm UTC
Using flexible rods for the side is an interesting idea. I had originally nixed that idea because then the sphere wouldn't support my weight when inside it. But if I make the hamster wheel part out of rigid rods and then using flexible rods for the hemispherical sides then that would work fine.
The key there is to find rigid rods and flexible rods that look like they are made of the same material. Ideally, it'd be nice to have both types of rods be transparent (like lucite) because I think that'd look very nice.
I don't know the various material types. If you look at the order page:
and click the materials drop down list, can you tell what each of those materials is? Some are labelled as clear, but can you tell which ones are rigid (with a half inch diameter) and which ones are flexible (with a half inch diameter)?
I've already ordered a few of those rods just so I can see what the materials feel like. But I only selected 5 types and the materials list is pretty long.
20 Sep 2007 00:14 UTCThu 20 Sep 2007 - 12:14 am UTC
It's part of a Halloween costume where I'm dressed as one of the monkeys from the video game Super Monkey Ball. In that game you're a monkey that runs around inside a ball. So for this costume I'll be a monkey running around inside this thing. It might be acceptable to just stand inside it and shuffle around, but I think the costume would be cooler if it actually rolled while I was running inside it.
Having internal connectors might make it roll smoother (no balls would be hitting the floor as it rolls), but I'm not sure how I would cut out those Y-shaped pieces. Cutting them from something means that they'd be square. I guess maybe a square connector could grip the insides of a round tube, but I imagine it wouldn't be a strong grip where an adhesive would actually help much.
When the rods that I ordered arrive, hopefully some will be rigid and some flexible. If not then perhaps I could just use smaller diameter rods for the curved parts (which should be more flexible) and thicker rods for the hamster wheel part.
If it was just a sculpture then making the whole thing a buckyball would probably be prettiest.
20 Sep 2007 07:46 UTCThu 20 Sep 2007 - 7:46 am UTC
myoarin, do you think you can do the angles that I asked for in my previous question? I'm curious about them even if I'm probably not going to use them with this modified version of the project. If you figure them out I can repost the previous question.
21 Sep 2007 07:48 UTCFri 21 Sep 2007 - 7:48 am UTC
I'm glad to see the giga-ball. I'll consider that my backup. If I can't get my own ball made in time (or if it turns out to be far too difficult) then I'll buy one of those.
24 Sep 2007 15:52 UTCMon 24 Sep 2007 - 3:52 pm UTC
I've looked into several options which I'll present here, but in my opinion all except the last have practical problems. The structure needs to be fairly light for several reasons: it must be able to roll easily without damaging the floor, it should not crush someone's foot, etc. Also, you probably need to be able to disassemble it easily for transportation (or to fit through doorways). I fear that a buckyball with its numerous rods and joints may be too cumbersome and heavy.
If you want to start with a hamster wheel and build it out with rounded ends, you have probably considered something like a carbon nanotube shape, with the tube part being very short i.e. just the rolling hamster wheel part, and each end of the tube being capped with half a buckyball. Here's a picture (but imagine the tube being much shorter):
Carbon Nanotube Molecular Model Kit
As myoarin says, you can cut a buckyball in half, and the cut will sometimes pass through the vertices and sometimes will pass midway through the edges. That will match up with the hexagons in the tube part, but it's not good news because it means the tube part won't roll very well. Take a look at the animation on the following page to get a feel for how roughly the middle part would roll:
Wikipedia - Carbon nanotube
You could work around this by making the tube part be a true circle, but then it won't line up with the buckyball halves. That's because every vertex of a buckyball lies on a sphere, but the midpoints of the edges (where some of the cuts to the buckyball will be made) don't lie on the same sphere (they lie on a smaller one).
If you had a bit of flexibility in your end caps, you could attach them to a circular hamster wheel like the one in the boston.com article that you referenced. The small photo in the top-left of the following article shows how half a buckyball has been joined to a circle:
Model buckyball tops Bristol nanoscience lab
If you're using a buckyball, I have been able to work out the angles to drill the holes into the balls that would sit at each vertex.
First, drill a hole from the "equator" of the ball into the center. Then, rotate the ball 120 degrees on its polar axis, and drill another hole from the equator into the center.
Now, use this second hole as the axis of rotation and rotate the ball 41 degrees 49 minutes on this axis. What we have done here is to "adjust" the orientation of the ball from the plane of one hexagon to the plane of the adjoining hexagon of the buckyball. Using the polar axis again (but the "new" polar axis obtained after the previous rotation), rotate the ball 120 degrees and drill the third hole.
The significance of the angle (41 deg 49 mins) is that it is 180 degrees minus the angle between adjacent hex-hex planes of a truncated icosahedron:
Polyhedra - Truncated icosahedron
I do feel that a buckyball-based design will be too unwieldy for party use, and I would like to present a much lighter and simpler design based around plastic water pipe - the kind of pipe that is used for water reticulation inside the home. It's light and fairly stiff, yet flexible enough for our purposes because it can easily be bent into a circle of diameter 6 feet. It's relatively cheap, and readily available from building supply stores or "Home Depot" type outlets.
Start with two twenty-foot lengths. Lay them on the floor parallel, about 18 inches apart. This will form the hamster wheel part. Cut eight pieces of wooden dowelling, each about 22 inches long, and lay them on top like railway sleepers, equally spaced (each 2 and a half feet apart). Ideally the dowelling will be of a diameter that will fit inside the plastic pipe. Attach the railway sleepers somehow - I would just bind them with tape. Each "sleeper" will overhang the "railway lines" by about 2 inches on each side - that overhang will be what we used to join the pipes that will form each hemisphere.
Now roll up the construction to form the hamster wheel. Join the ends of the 20 foot circumpherences by inserting a short length of dowel into the join and stapling it, then taping the join.
To build out the sphere, use eight ten-foot pieces of plastic pipe, four per side. Bend each of these into a semicircle, slip the ends over the projecting ends of the "sleeper" dowels, staple and tape.
Now all that's left to be done is to provide a walking surface for the wheel. It's tempting to use "boards" as you mentioned in your question, but this will be heavy and will complicate the construction. I'd be tempted just to cover the outside of the hampster wheel with fabric (e.g. strips cut from old sheets). When you walk inside the wheel, you step on this fabric to bring a new part it to the ground with each footstep - but the fabric doesn't need to support your full weight because your foot will be pressing directly through it onto the ground.
Add some lighting using the EL wire suggested in the responses to your other question, and you will have quite a spectacular wheel that can be disassembled and transported without too much trouble.
I hope this addresses your needs. If not, please request clarification.
GOOGLE SEARCH STRATEGY
half model nanotube buckyball OR icosahedron
This Wikipedia article confirms that every vertex of a buckyball lies on a sphere:
Wikipedia - Truncated icosahedron
Also this page includes some worthwhile links:
Nanotubes and Buckyballs
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