It is time to revisit the mechanism that will move the fins. My primary reason for building this particular project was to learn mechanical movements. After I finished sculpting, I set aside a week to really figure this out.
The objective is a caterpillar motion, with a change in speed, that varies between a small flutter and a large sweeping motion, and these two motions cannot be synched. My engineering friends Kim Hall, Paul Illian, Pasha Amigud, and Bill Jeswine offered abundant suggestions. We began with frantic scribbling on napkins and available paper, accentuated with lots of hand movements and shuffling through the Grainger Catalog.
The next step was to build a super-rough prototype from available steel, bolts, screws, wood, glue, baling wire, and PVC. Have a look at it after the jump.

We assumed it would take at least three attempts to get it working and ten more to get it right. These photographs show our third attempt. The concept is good, the size is about right, and it works!

The fin mechanism prototype in progress

So far, this has taken about 40 hours. The next step is to make all the parts out of much more robust materials: rod ends, bearings, pillow blocks, steel and ultra-high molecular weight plastics.