Creating a 3D Printed Rattleback

Today's guest post is by Nick Stone, Z Corporation Mechanical Engineer.

I came across this toy in a science museum gift shop when I was a teenager. It's a simple canoe shaped piece of plastic that performs miracles. It's called a rattleback and it has amazed people for thousands of years.

Spin the rattleback one direction and it just keeps going. Spin it the other way and it slows down starts rocking, and then, as if by magic, turns back the other direction. Start it rocking and it will begin spinning. The magic is in the weight distribution. It causes the rattleback to have a preferred spin direction. If you spin it in the other direction the rotational energy converts to rocking energy and then back to rotational energy in the other direction. And frankly that's the best explanation I can give because I really don't get it. Oh well, it's still a lot of fun.

I've wanted to print one for quite awhile now and after a bit of trial and error I got a shape that works pretty well. The great thing about having a ZPrinter at my disposal is that I can run through revisions so quickly. I'd say I went through 20 different revisions before I was happy with it. Because the strength of zp150 parts is so high, for a lot of the early revisions I didn't bother to infiltrate. I just depowdered, gave it a spin, watched it not spin back, and then tossed it in the trash.

This model is about 4 inches long but I've scaled it up to 26 inches and all the way down to 1 inch. It seems to work better the larger it is. The surface finish is important so after a dip in ZBond 101 I smooth the bottom with fine grit sand paper. I get about a half turn back from the 4 inch version. Let me know if you can beat that.

Here's a video of a 26 inch model we printed on a Z810. It actually shakes the table when it starts rocking.

http://www.zcorp.com