Several years ago at a conference I met a professor of acoustics from Japan who was demonstrating a folk toy called the “Giri-giri gari-gari”. He said it was so simple to make that anyone could do it without any measurements. I had to try it out!
After doing a little googling, I found out that the toy is also common in other cultures. In Appalachia it is known as the “Gee Haw Whimmy Diddle” (or the Gee Haw Whammy Diddle with various spellings of Whimmy or Whammy).
The toy is simply a stick that has notches cut along its length with a propeller attached to one end. The stick I chose was a square dowel. I used popsicle sticks for the propeller with a nail for the axle. I drilled a pilot hole to get the nail to seat without splitting the wood. The propeller spins when a small stick is slid along the notches. By adjusting how you slid the stick along the notches you can control the direction of the spin.
Here’s a video of me trying out one that I made in my office:
(Yes, I dropped the camera. Twice.)
I still need quite a bit of practice, but I can give you some tips if you want to make your own.
1. The notch spacing and the depth do not matter at all. Make them deep or shallow, as long as you are getting vibrations into the stick it will work.
2. The closer you can make the notches to the propeller the better it seems to work. There is a trade-off in making the notches so close to the propeller that you tend to hit them with the stick more easily.
3. The further back you hold the toy from the end with the propeller, the easier it seems to be to get the propeller to reverse. This is probably due to the increased transmission of the vibrations down the length of the toy.
4. The better balanced the propeller, the easier it will be to spin, obviously. It seems that the shorter the propeller is, the more easier it seems to be to get it to reverse. However, I think the shorter propellers are less dramatic.
This was a fun project to make, and I have fun playing with it!