The Cats Found Them to be Amusing

This X-Mas I was looking for something simple that I could have the 'Bot make that our department cold give out as presents. I decided that a "two circle roller" would be perfect. This device consists of two disks of equal diameter joined to teach other in a perpendicular orientation such that the distance between their two centers is √2 *radius. This arrangement has a center of gravity that is a constant distance from the surface it rest on. The result is that it rolls effortlessly on any flat surface. Check out the Wikipedia entry on the oloid - a similar device.

For this project I used 0.245" Komatex that was used as a graphic substrate in a past exhibit. I settled on a 3" diameter that would be a reasonable size for the toy while giving me 19.5 units/sheet. The above cut preview show how the majority of the disks share a cutting path for the assembly slot. This saves some time because the tool leaves the material fewer times. I probably should have duplicated that technique in the first and last rows in a horizontal fashion, but I got lazy.

This detail from PartWorks shows a subtle detail that allows the disks to snap together. A small smack with a rubber mallet is all that is needed to join them.

Here is a video of the finished product:



I placed one in each staffers mailbox the week before the holiday break. I didn't include any documentation, because I wanted people to have an "ah-ha!" moment when they discovered the properties of the device. I thought that it would be fairly evident - I had a hard time keeping them in the mailboxes as they kept rolling out. Unfortunately, most thought they were puzzles and (with some difficulty) took them apart.

I sent out a mass email about the gift, and suggested that they would make ideal cat toys. They were then very well received.