Thus spake "Gerardo @neorigami.com" <[email protected]> on 8/7/16 9:15 AM:
> I wanted to ask you, what are the mechanics behind the flapping bird? Are they > related with the simple machines? I couldn't find one that fits. Many years ago, I got interested in action models and started looking at the mechanisms used in various flapping birds, with the goal of identifying a mechanism I could extract and re-use in other designs. The traditional Japanese flapping bird was an obvious first place to look. It turns out have a surprisingly complicated mechanism. As Judith pointed out, there's something of a pulley system, as layers of paper slide over other layers near the bottom of the bird (which is where it often rips). This bird is famously finicky to get to work properly; a bit of curling of the wings often helps. In the engineering of origami, there is a concept called "rigid foldability"; an origami pattern is rigidly foldable if it can move with all facets remaining flat and planar and the only bending happening along the creases. The traditional flapping bird is not rigidly foldable, because various facets curl and bend during the motion, but it's possible to add additional creases to get a clean, rigidly foldable (but still fairly complex) motion. Another nice flapping bird is Stephen Weiss's (from Wings and Things). It, like the traditional bird, is from a Bird Base, but is more foolproof because of some extra layers reinforcing the stress point, and it always flaps without any finicky tweaking. It's no harder to fold than the traditional bird, so I think it's actually a better teaching model. Ligia Montoya's Flapping Bird (from Secrets of Origami) had a nice flapping action, but it actually required that folds roll through the paper. This breaks rigid foldability, and also wears out the paper pretty quickly. There were also a few flapping birds in The Flapping Bird (a origami periodical of the 1960s), that I looked at, but that didn't seem to have usable/clean mechanisms. However, Randlett's Flapping Bird (from The Art of Origami) was ideal! It has a very clean mechanism and can be made rigidly foldable. In fact, I've made versions from matte board with taped creases, and wood veneer with ripstop nylon creases, and they work very well indeed. The mechanism from Randlett's bird is also easily isolated, extracted, and re-used. I used that mechanism in my Violinist, Bassist, Pianist, and Viking Ship (although the thickness of the paper doesn't make the behavior as nice as I would like.) (I also tried to use the mechanism to make the pendulum of a ticking grandfather clock. That didn't work out, but once I had a nice clock face, I started looking for other things to do with it, and certain other clock designs ensued.) More recently, I looked at whether I could boil down that mechanism into a simpler bird that still flapped; that resulted in my RiF-RiF (Rigidly Foldable, Rigidly Flapping) bird, which also works nicely even from rigid materials with flexible hinges. As Kenneth Kawamura said, the field of study of "mechanisms that move" is called kinematics, and is part of the field of mechanical engineering. As it turns out, later this month, the American Society of Mechanical Engineers is having their fourth annual Symposium on Origami Design in Charlotte, NC. I expect there will be quite a few papers on rigid foldability, but maybe not so many on flapping birds in particular. Regards, Robert
