Following is the video in two parts showing the operation of the tail on Faux Fish. For the demonstration I operated the tail using two pneumatic cylinders. This eliminated the need to manually pedal the tail. Some day I would like to actually test Faux Fish in the water using these cylinders as they can produce much more force than a pair of legs. As I mention in the video the water resistance smooths out the movement of the tail and also acts as a lubricant in the plastic bearings to eliminate the squeaks you hear. For really quiet operation and a lot of money I could use linear induction motors to drive the tail. The tail is currently set up for maximum amplitude. This can be adjusted by limiting the stroke on the air springs and/or the drive cylinders_
The advantages of using the air springs is the ability to easily vary the spring rate and to be able to change it while underway. You could start out using a low pressure and increase it as you accelerate, varying the rigidity of the tail similar to what a real fish does.