This surf-and-turf robot swims using ribbon-like fins. And it's floated for US Navy approval In Henry Wadsworth Longfellow's poem "Paul Revere's Ride," light from lanterns served to signal how British troops would arrive at the start of the American Revolutionary War: One if by land, two if by sea. In wars to come, US naval robots will traverse both. At the 2017 Naval Future Force Science and Technology Expo in …
was developed in the mid 60''s for use in prosthetics.
The design was literally a nylon stocking with a balloon inside it driven by air pressure (< 3 atm, which is low for pneumatic systems).
It was later used by Shadow Robotics to develop huamn scale (in size, weight and strength) robots.
I'm not sure how non linear it was.
This very much was ringing a little bell in my mind. It is really just a few of these in a line.
The main thing this reminds me of is the wonderfully named Black Ghost Knife Fish - a member of the electric eel family and quite spectacular to watch. Essentially, it has a single "fin" running underneath it, which it oscillates in much the same way as I'm guessing that robot will.
https://www.youtube.com/watch?v=gimQjPkvsNIv
It also means that unlike other fish, they're able to move backwards very easily, by reversing the oscillation...
I recall seeing an illustration of a boat constructed by the Tissandier brothers in the late 19th century that was designed to test a propulsion system inspired by the way fish swim. The thing had a central longitudinal well, above which was mounted a fore-and-aft horizontal rod. On this rod were pivoted a series of vertical shafts attached to a long strip of stout fabric. Shafts and fabric extended through the well into the water. The drive train caused each shaft to swing back and forth in sequence, causing the fabric to undulate rhythmically and drive the vessel forward. It is said to have worked well, though it has obvious disadvantages for many of the purposes for which you'd want a boat.
I ran into this in an ancient bound volume of Scientific American, a long time ago. I'm surprised that it has not made its way into Wikipedia, which recognizes Gaston and Albert Tissandier primarily for their contributions to aerostatics.
...I'd be concerned about the number of moving parts in the final drive mechanism.
With a standard propeller system the final drive mechanism consists of the rotating drive gear/prop-shaft/propeller assembly, which operates as a single unit. With this system though, it looks like there are eight independent reciprocating drive servos, and their associated hinged actuators, per side. In addition, every time the drive actuators cycle, the flexible membranes or 'fins' are put through a corresponding stress/de-stress cycle.
The comparatively large number of moving parts in the final drive does not bode well for reliability and the reciprocating/hinged movement modes are not good from a wear point of view. Dunno how well the flexible membrane will stand up to fatigue.
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