Rattleback

[bergerud]

Here is a curious thing for a weekend project. It is called a rattleback. If you try and spin it, it will wobble and rattle until it changes direction and spins the other way. It will spin fine one way but not the other. (Another one of my student demonstrations.) It is a forgiving double sided carve since the sides do not need to line up exactly. If you have a nice small piece of exotic wood (denser is better), this is the perfect use for it. There are two versions, one nice and smooth and the other a "voodoo" version. (The pictures are of a smooth one made of rose wood and lacquered.) They are very easy to finish and make great little gifts.

This is my own mathematical surface that I created in a math program called Maple. Imported using the STL importer.

http://youtu.be/OHCc22r329Q

[brdad]

I have some of these in plastic, they are interesting. I often wondered how a larger one would work, now I can find out. Easy to see these are much classier in wood. Thanks for sharing.

[aokweld101]

what are the uses for the rattleback, never heard of it. is it just to look at?

[bergerud]

what are the uses for the rattleback, never heard of it. is it just to look at?

It is a 200 year old toy to amuse children. Its strange behavior still intrigues scholars today. Scientific papers are still published as people try to computer model the behavior. Can you explain why it does what it does?

[brdad]

I had some free time tonight so I carved the mask version of this tonight while cleaning up the basement shop. I used a scrap of maple and it came out nice, and I think I'll make a few more, probably the smooth ones but with darker wood and centerline names or windings of some sort. I think I'll also make a simple sled so I can carve them at 90° to cut down on a few minutes of carving time.

I questioned why the feather was not set to 0 to also help with carving time, and was surprised to see it actually estimated a longer carve time with 0 draft. But, carved at 90° setting the draft to 0 decreases the time, I'd guess because there are several passes on each side of the project across the X axis that serve no purpose than to carve the draft.

Anyway, thanks again for putting out this project.

[bergerud]

The feather is just to be easier on the machine. I do not like the bit plunging at the beginning and hitting a wall of wood on each side as it goes.

I like the idea to carve it sideways. I would worry a little about the line up. The x cannot be trusted to be as accurate as the y. Let me know how that goes.

[blhutchens]

Does anyone..... have an idea of how to make one of these that is a "rare celt" that will change rotation when spun from either direction and change directions several times during one spin?

[bergerud]

Let us know how that goes.

[oscarl48]

First attempt: complete failure.

I screwed up and re-shifted the center of mass back to the center when I was cleaning up the mesh without realizing it. So I pretty much carved a symmetrical pattern. It likes to spin clockwise perfectly and it likes to spin counter clockwise perfectly. If I put a twist on it, it would make a great propeller.

Back to the drawing board. This time I am not going to re-shift the center of mass.

[oscarl48]

Well, success. They work the way they should with off center of mass rotation. Preferable rotation is opposite of each other. After a sanding I applied some lacquer and waiting for them to dry.

Please let me know if anyone wants these patterns.

But honestly, Dan's pattern is more elegant and it is also a lot more aggressive than my version. You can get the same results from Dan's by mirroring the pattern so that you have one of each with different rotation preference if you want.