The Manta Drive: proof-of-concept for an ROV propulsion system.

Every submersible vehicle has weaknesses. Everything that pierces the hull (door, cable) is a potential leak, and if something must both pierce the hull and move at the same time, the potential for leakage is multiplied.

This Instructable outlines a drive system that eliminates the need for drive-shafts to pierce the hull of an ROV ("Remotely Operated Vehicle" - a robot submarine controlled via wire), and also removes the very real possibility of rotating impellers getting tangled or jammed by underwater plants or hanging lines.

It could also give rise to vehicles that have a much less damaging effect on the habitats they are used to investigate, because of the lack of a "wash", and because the lack of rotating impellers will reduce the risk of injuring animals the Manta Drive encounters.

Step 1 The concept.

The whole idea of the Manta Drive was inspired by a visit to an aquarium where members of the public got a chance to pilot small ROVs round an obstacle course. I got my first look at the ROVs and realised two things:

• There were a lot of places for the water to get to the insides of the ROVs
• The ROVs didn't look right - they were just boxes, and didn't look designed to swim. They lacked the elegance I associate with swimming animals.

Later cogitation also came to consider power - the high-revolution impellers used by the ROVs struck me as power-hungry. I may be wrong, and I have not tested the power consumption of the Manta Drive, but this is a secondary consideration.

As I wandered the aquarium, the ROVs played on my mind, and I found myself comparing them to each animal I saw. How did they compare? Could the animal's swimming motion be replicated elegantly, in a way that maintained hull integrity*?

Looking at fish like rays, sea cucumbers and stonefish, I realised that the most elegant propulsion method was the waving fin.

I also realised something important - fish don't leak. A rotating shaft needs to pierce the hull completely, working through a hole in the hull. On the other hand, a reciprocating motion (up-and-down) could work through a flexible, waterproof membrane which did could be fixed firmly around any moving parts without ripping.

I further realised that flexible membranes could wear out, but magnets don't, and magnets can act through any non-magnetic materials without restriction. Make the hull rigid, but non-magnetic, and the risk of leaks due to the drive system are completely eliminated.

_{* Oh, I went all Star Trek for a second there!}

Comments

[macrumpton]

I love this project, although to simplify the drive mechanism I think having the crankshaft outside the hull would be easier to build.

[Kiteman]

Putting it outside would need something to pierce the hull, which defeats the object.

[Asa J]

Biomimicry, awesome. This design is closer to a cuttlefish propulsion. i read about a fish that has similar fins on top and bottom and can move in any direction without changing orientation. I.E. vertically while remaining horizontal. I think that movement was achieved by ripples originating at the extremes of the fins moving towards the center causing a vortex above the fish that sucked it upwards. Don't quote me on that but it was something like that. I wish I could remember what kind of fish it was, it would be really useful info for you I imagine.

[Kiteman]

Boxfish?

Sunfish?

[senchele]

I thought of doing this same thing several years ago! Way to go!! I didn't think about using magnets. I figured using a long cam in the middle would reduce weight and give the same effect. I would dream of using it for submersibles, as well as air craft. Carbon filaments epoxied to thinfilm. I also thought it would work the other way around, and place the membrane inside a tube and jet the water/air through it. I never got to try it, but it is nice to see someone else working on it!

[Kiteman]

Thanks.

[DehLeprechaun]

was thinking of using this kind of propulsion for a rc air ship someone has technically already done this but mine will be steampunkish here is link; http://www.youtube.com/watch?v=UxPzodKQays

[el_roboto_loco]

Wish I had seen this instructable a long time ago.  A couple years ago I made a proof-of-concept for a magnetically coupled fish tail with no mechanical coupling between the tail and the drive mechanism.  The fish tail shown is on a metal swivel, but the next thing would be to eliminate the swivel and use something flexible, probably just the same material as the tail.  The idea was to make a propulsion system that would be very quiet, i.e., stealthy.  I used a servo motor rigged to spin constantly with neomagnets mounted on top, and with neomagnets also mounted on the tail.  Next I wanted to try electromagnetic coils so that there would be no noise from a motor. 

http://www.youtube.com/watch?v=NohFbnIj7GE 

[Kiteman]

That's nice - does it actually move?

[el_roboto_loco]

Yeah, it actually moves.  Works just like a fish.  Of course it needs a lot of refinement.

[k0ldburn]

I just had a thought about this. What if the wings weren't made watertight and adjusted to changes in pressure naturally, but then a center hull had a master ballast system like a normal ROV that could push the craft close enough to the surface to be retrieved? The cavities of the wing should be able to equalize to the pressure outside the craft quickly enough to adapt and not be crushed, right?

Also, I remember hearing about Speedo making a new nearly frictionless bodysuit that sparked some controversy for helping as many people break records as it did. It's just a thought, I'm in no position to spend $257+ on a pair of shorts to destroy for an ROV concept. If it isn't usable, what about normal wetsuit material?

I like this idea and I'll definitely try to push it further as soon as I have time and materials. 

[ultimachris]

wow, very impressive... i will definitely be taking this concept further.


How do you think turning will be handled?- you can't turn with both wings doing the same thing.


I'll keep you posted

[Kiteman]

I thought of running each wing separately - look at the bottom-right of the sketch in step 8.

I was just proving an idea, though - others (you) will be able to take it much further.

(Don't forget to post an Instructable.)

[eyerobot]

What about using some form of latex as the shell of this vehicle?

[albylovesscience]

wow talk about the next davinci

[sh_joe]

So, you basically want to build a Festo Ray:

http://www.festo.com/inetdomino/coorp_sites/en/c79c5d07d5805095c12572b9006f04f5.htm

[hardlec]

I hope this is not too late: It would be interesting to see how well this will work. The idea of a "swimming" ROV or MPV is quite interesting. Magnetohydrodynamics has been disappointing. Propellers have hit their development limit. Have you considered making your "joints" linear induction motors?

[Jaycub]

This could be simplified even more by just using one rib, and having the rest of the wing trail it and pivot on it freely within the range allowed by a "pizza with slice missing" shaped blocker.

[setok70]

can you use gear system like in the ornithopter to produce the up and down motion for the propulsion. I been working on my own idea in the same general direction I stuck with the up and down motion with the idea that I have . I like the design and good ideal. WELL DONE

[crapflinger]

you could do this without the possible drawbacks(and possible fin loss) of the magnet concept by just sheathing the entire ROV in vinyl or latex or something...so build mechanically attached ribs that could be independantly controlled or cam controlled or whatever controlled then just cover the whole thing with a flexible skin...it would probably be easier to accomplish turning without having to muck with the magnet parts...

[Kiteman]

The trouble with flexible skins is that pressure deforms them, and the deeper the ROV goes the greater the pressure, and the greater the amount of deformation on the skin. This would eventually split the skin or jam it in the moving parts.

[mwwdesign]

What if you had everything inside working in liquid (maybe that 'dry water' used in offices to extinguish flames without water damage) as well? Fish don't deform because they have (uncompressable) liquid inside - maybe that's the key?

[corey_caffeine]

mineral oil

[Kiteman]

If you fill it with something besides air, you're going to run into buoyancy issues. Plus, part of the reason for producing this concept was to keep cost and complexity down for amateurs.

[silverbyte]

i heard you can use ammonium chloride to solve your buoyancy problem. Apparently this allows some squid to submerge several thousands of feet deep.

[mwwdesign]

Fish don't have buoyancy issues... and before you might bring up swim bladders, etc; using a liquid of similar density should cause no problem - it would make it easier to dive/maintain depth below the surface than using air which would make it want to rise to the surface all the time (unless it is counteracted with more weight = inefficient). This method of propulsion is not for use on the surface.
I don't see this being any more of a problem for amateurs than any of the other issues that are being struggled with so far. There are always 'issues' no matter which way you go.

For reference, your response was a bit abrupt - I was merely making a suggestion.

[Kiteman]

Read it all together - your post and mine - it's just a reply, nothing abrupt intended.

[mwwdesign]

No probs then.

[crapflinger]

also kite...i don't want my comments construed as saying your idea is crap....it's a fun method of locomotion..just trying to think of ways to avoid the drawbacks... such as: what happens if something hits one of the ribs and knocks it off of the body of the "vessel"? how would the force of the water change the way the ribs are moving? etc..

[Kiteman]

That's something for future work.

I wasn't planning on holding the ribs in place with magnets, the point is that magnets allow mechanisms to "penetrate" the hull without presenting a leakage issue. Maybe strap them to the outside of the ROV?

I think that, underwater, it would be possible to produce a more efficient, rhythmic motion if there was some resistance to the ribs - it was hard to produce a nice wave for the video because there was nothing pushing back against the ribs.

[adrian.robb]

you could probably quite easily have a propeller driven by the magnets. eg:
(looking along where the shaft would usually be)
O
|
O----+----O
|
O

O = magnets

have two of the above thingys, one inside and one outside the hull, with the external + connected to an axle mounted in brackets with bearings and the external axle is connected to the propeller, and the internal + is connected to the motor.

follow that?

[adrian.robb]

sorry, my magnetic coupling ascii didn't work. it was meant to look like a cross, not a T on its side

[Kiteman]

I got what you meant, and people do use that. I was after something more biomimetic.

[fuzvulf]

love it, just need to make the ribs spin slowly and you have a remote controlled marshmallow toaster. Not making fun, the U.S. Navy is working on a robotic tuna, And they guarantee it is mercury free. would make a dar n crunchy sandwich though. Oh, in reply to "drofenvy" yes you could use emagnets but the amount of Amps required to get the 14000 Gauss you get with a mid range neodymium would create so much E.M. hum that any sensitive equipment nearby would have to be heavily shielded. Kiteman, I think you should go ahead and build it. Use a arduino to control six servos with the magnets on the ends of the horns two more servos for the "fang" looking things on the ray and tail and a body made of silicon rubber with a dry suit seal for the guts. House all the stuff in some PVC and take the thing to your navy, tell them you never liked tuna.

[Kiteman]

Thanks for the positive comment.

My problem is, I have so many projects I ought to do, I never seem to do any of them...

[drofenvy]

Instead of using permanent magnets for the inside and outside connections, why don't you use electromagnets for the internal connections? You could make a stronger magnetic flux, and you may be able to get more force on the outside ribs.

[Kiteman]

That's possible. This is, as I said, merely a proof-of-concept. I'd be bothered about power with e-mags, though. Unless you powered it via the umbilical, so battery-weight wouldn't be an issue...

[superasian33]

thats cool, and i like the magnet idea. but replicating non-propeller propulsion similar to this has proven to be difficult. how do you know your design would work well underwater? do you plan on testing it, and if so, how?

[Kiteman]

I don't know, but I strongly suspect.

The first step was to make sure that the model I had in my head actually produce the motion I wanted.

That's what this model is for, and it works.

To take things further, I need to see what a basic ROV needs to be capable of. I have tried contacting several ROV manufacturers and public aquaria that I know use ROVs, but I have yet to have a response.

I will also need money, and the bank balance is a bit dodgy for the next few months.

[Senator Penguin]

I've worked on an AUV (an autonomous ROV), and generally speaking, the vehicle must be able to move forward/backward, turn, and also control depth with some sort of vertical thruster. And if you want a magnetic compass which most ROVs and AUVs have, you need to compensate for magnetic fields (moving ones are much harder).<br/><br/>I suspect that power would slightly lacking underwater with this drive system, it appears that the magnets would have trouble moving the water with a sufficient amount of thrust. The water provides a huge source of resistance to not only the body of the ROV, but the moving parts, especially the membrane. The magnets might not create enough torque on each rod to push the membrane almost perpendicularly through the water. Perhaps reducing the distance between the magnets would help. Of course, this model is far smaller and cruder than an actual metal/plastic/greased implementation, so efficiency would greatly increase.<br/><br/>Our propellor based thrusters needed over 1 ft/lb of thrust in order to move our quite small AUV barely through the water, if that helps with any calculations.<br/><br/>If you want to see ours, its at <a rel="nofollow" href="http://www.avbotz.net">avbotz.net</a><br/>I remember the team from UColorado Boulder had a sub with normal propellors, but turned using a "squid" propulsion system, which is the most practical life-inspired system on a sub I've yet seen.<br/>