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S:UFA Swimming Underwater Fish Analog

Fishy Propulsion With No Moving Parts
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Please bear with me. I've been working on this for years but do not have the tech to see if it actually will work. I don't see why not, but I await comment. Just below the right and left lateral lines of a fish-body silicone shape, neodymium magnets are implanted. Deeper in the body, along the central 'spine' many pairs of fine wires are implanted near, but not touching, the magnets. If minimal voltage is applied to a magnet's associated wire, it will cause the fish-body to bend/contract at that point. A pulsed voltage to sequential wires along either side of the length of the fish-body creates the wavy motion we associate with fish motion. So far so good. The problem with fish analogues has been that the swashing of the body and tail only affords movement like a grouper or goldfish, not the blazing speed of a mako shark. This is due to the frequency and amplitude of the muscle contractions; an increase in speed requires a large increase in frequency, but also, critically, a non-intuitive decrease in amplitude. Solutions to date have only achieved slow-speed mimicry and default to propellers for any real speed. In the S:UFA the variation in voltage intensity and location makes possible either a swashing, slow-speed grouper-like motion, or the startling speed of the mako. At high speed a fish's body is almost shivering rather than swashing, and the 50mph speeds of the dorado and mako cannot be achieved only by moving the tail back and forth. The entire length of the body has to participate to achieve the laminar flow necessary for blazing speed. The silicone body of the S:UFA contains the battery and propulsive electromagnetic gear, and is self-contained and waterproof. It is paired with a head end that has the brain and sensors. As to scale I don't see why these couldn't be any size from 6" to 6' or larger. Casting the silicone body with all the propulsive gear and wiring inside and the ability to change out the head end for mission-specific goals is a plus. Also: No moving parts except the silicone. Could be a toy. Could be a research tool. Could be a weapon.
minoradjustments, Jul 27 2023

Magnetically Controlled Soft Robotics Utilizing Elastomers and Gels in Actuation https://onlinelibra...1002/aisy.202000186
[a1, Jul 27 2023]


       [+] This could work. See first link for other soft, magnetically controlled robotics. The idea of a completely sealed unit with internal electromagnets is good.   

       But how will you adjust buoyancy?
a1, Jul 27 2023

       "As a result, magnetic actuation has successfully demonstrated swimmers, crawling devices, and micropumps..."   

       Terrific article. Interesting mechanical solutions. Flagella, for god's sake. They are still swashing around, though. Or flexing/unflexing. Very slow. They're pretty much working on the micro machine scale for medical applications. I propose air chambers between the magnets to facilitate bending and smoothing out the motion, and a spine of varying flex molded in to allow for a wide range of speeds, smoothly adjustable. (A 90° rotation mimics the motion of whales and dolphins.) That 'shivering' is the goal for high speed, and none of the current solutions address it. It could be done mechanically but that would be noisy. This is meant to be totally silent.
minoradjustments, Jul 28 2023

       I'd adjust buoyancy the same way subs and fish do it. By varying the volume of air and water inside. For small sizes you would only establish neutral buoyancy for the depth you wanted to work at, and depend on motion to change depth within a range. For greater depths and ranges there would be an air bladder and iron shot controlled magnetically in an emergency for surfacing.
minoradjustments, Jul 28 2023

       If you want to get a little more exotic (=$$$), shape-memory alloys or piezo-polymers could be a solution (especially for initial small-scale builds). I had a quick dig for response times & frequencies but didn't come up with anything useful.
A lot of the medical-type research has the robots actuated by an external magnetic field (ie. a fixed static volume & a lot of the complexity NOT part of the robot itself) which is not the droids you're looking for.
neutrinos_shadow, Jul 28 2023

       // varying the volume of air and water inside //   

       Yes, that’s how bony fish do it but they’re not completely sealed units as I thought you were proposing. Will SUFA have some kind of gills to extract dissolved oxygen from the surrounding water?   

       Cartilaginous fish (sharks) without swim bladders are a bit closer to your latter proposal - close to neutral buoyancy and they have keep moving or they sink. But that strategy would limit the range of your battery operated swimmer.
a1, Jul 28 2023

       There are quite a few ways to change volume without extracting anything from the outside water...   

       1) Resizable vacuum balloon (doesn't actually need to be a vacuum, but this is the HB)
2) Water electrolysis / hydrogen - oxygen combustion (or the equivalent with a reversible fuel cell)
4) Using a pressure tank and a flexible bladder and a compressor (way too practical)
3) Vaporizing a liquid
4) Heating a solid or liquid with large coefficient of expansion
5) Freezing water
6) #4 + #5 (using a Peltier junction of course)

       One wonders why you would even bring up such a simple problem on the halfbakery.
scad mientist, Jul 28 2023

       // why you would even bring up such a simple problem //   

       No offense meant, shirley. Working out “problems” (or details, challenges, considerations - use any word you like) is kneaded when baking an idea with so many ingredients.
a1, Jul 28 2023

       The rad version of a buoyancy compensator would be a solenoid or other type of small valve on a CO2 cartridge that fed the bladder. Another valve could evacuate the CO2. Any really deep work would require a lot of pressure to stay neutral, so the bladder should be as small as possible. The greatest percentage change between depths happens in the shallow waters; at 33' pressure is 2X ATM. At 66' it is 50% greater than that at 33', not double the 33' pressure. The rest of the S:UFA should be non-compressible. I'm trying to avoid any mechanical movement to absolutely bring the noise down as far as possible. Same for metal parts, batteries, connectors.   

       What is still the biggest question, I think, is how much power it takes in the electromagnets to get the amount of flex necessary to create propulsion. The timing of pulses, the controls, the valves and batteries are already in use in programming in the RC model universe.
minoradjustments, Jul 28 2023

       //5) Freezing water//
THAT I like! Have a cavity on the top of the craft that can fill/cover with ice when the system is activated.
Unfortunately it wouldn't be "fail-safe" (default (no ice) is denser than water so sinking...) but since when has that stopped us?
neutrinos_shadow, Jul 30 2023

       Needs paragraphs.
Voice, Aug 02 2023

       Thank goodness - a voice of sanity in the text flood.   

       Yes, just hit enter twice periodically.
normzone, Aug 15 2023


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