Building a Magnetic Coupled Thruster.

[sthone]

Ok, its been awhile (a long while ) since I have actually done anything Rov related so here we go....... This thread is going to demonstrate from start to (hopefully) finish the design and construction of the new magnetic coupled thruster I am working on. It will probably be a long thread but it is not meant to be a "how to" but is more or less just going to show how I go about the process. (this thread is also for me to help remember how I did things if it actually works out and I need to build more of them later on down the road.) Keep in mind this is a prototype and I really don't know how well (or if) it will work, either way this thread will show my success (or failures so that others won't make the same mistakes)

magthrusterplans.jpg (274.05 KiB) Viewed 7894 times

This is the basic design I will be working from and is subject to change through out the build. The basic principle as with most magnetic coupled thrusters is.... An inner rotor that holds one set of magnets is attached to the motor and is sealed inside the main thruster housing, the prop is attached to another rotor which holds a second set of magnets on the outside of the housing. This allows the prop to be coupled to the motor via magnetic force and eliminates any type of shaft seal. Basically there should be no way for water to reach the motor because it is totally sealed to the outside water. It is possible for the cap o-rings to fail but there is less chance of this happening over a shaft seal. The unique thing about this design is the fact that the whole outside rotor spins with the prop. I can't take credit for this concept though, I saw this along time ago on a set of drawings by Thijs Struijs and just changed a few things here and there. The other unique option I added was to thread the motor mount so the spacing between the magnets can be easily adjusted. I want to magnetic pull to be strong enough to turn the prop but I also want it weak enough to break away if the prop should become tangled. This way the motor should never be able to stall and draw to many amps.

magthruster001.jpg (116.44 KiB) Viewed 7894 times

These are the parts I have purchased all ready. The housing and rotor parts will be turned from a solid piece of 2" PVC Rod. I choose PVC because it is cheap and easy to machine. The motor is a Brushless Turnigy Multistar 2216-800Kv 14Pole Multi-Rotor Outrunner and I am using a HobbyKing Brushless 30A Car Electronic Speed Controller w/ Reverser for control. Not knowing much about Brushless motors and controllers yet I bought a Hobby King Programming Card too just encase it needs reprogramming. The Magnets are 1/4" x 3/8" Neodymium Magnets.

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I've never used brushless motors before so I want to make sure I'm not going to burn anything up before I machine up the housings. I bought a few of these Vex controllers years ago that should be perfect for testing out the new controllers.

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I also bought one of these hexTronik DT700 Brushless Outrunner 700kv motors because it all ready has a 4mm shaft. I want to test out running a brushless exposed to the water and this one should be the easiest to do that with because I can just trim down the shaft and screw on one of the many 4mm thread props I all ready have. (this is a thread for another day though)

[a_shorething]

Hi Steve,

Very cool that you're getting back into your development of the Mag-coupler. I'm looking forward to the results.

As you know I'm also working on a design. Lots of cool developments.

Game on!

[Toffe]

Awesome idea! I had my design a few months now but havent got it worthy of building.





But after i saw your's i redesigned the whole thing.




I am printing it right now on my 3d printer and i'll try to "build" a prototype tomorrow. If it works that is definitly the one i'll get machined ! Just have to find someone who can make "threads"

[sthone]

Yeah a_shorething I have been eagerly following your thread. Your design is similar to one of my old ones, it's nice to see that concept actually working.

setup001.jpg (117.37 KiB) Viewed 7822 times

I did a quick test setup today just to try out the motor. I'm definitely going to have to use that program card because it needs to complete stop and I need to release the stick before going in reverse. I think this has something to do with a brake feature. It also is not as powerful in reverse as forward either. Hopefully it's something I can program into the ESC I really haven't looked into the card yet.

setup002.jpg (127.44 KiB) Viewed 7822 times

On a side note I took this out of my motorcycle for testing purposes but this might be a cool little battery to use as on board power. It's made by Shorai and they call them Lithium-Iron batteries, this one is 14Ah and has 210 CCA (not really important here) but is only about 4 3/8" L x 2 1/4" W x 3 1/2" H and the amazing part is it only weights 1.5 lbs (which is super light compared to a lead-acid battery) It's a little big to fit in a 4" PVC pipe but I night have to make a housing for it and give it a shot.

[sthone]

Toffe, that's pretty cool you should start your own thread for that. (not that I mind you tagging on to mine) The only thing I might be concerned about is that the area around the prop rotor (so to speak) is going to fill up with water and might change your buoyancy.

-Steve

[SSN626B]

@Steve,
The Lithium-Iron batteries are not cheap: http://www.batterymart.com/p-shorai-lfx ... ttery.html This may not be the cheapest place to buy them. The chargers are not cheap either: http://www.batterymart.com/p-sho-bms01- ... arger.html However I think that the universal battery chargers used for charging LiPos/NMHi batteries may charge these kinds of batteries.
The specs say that they do not produce an explosive gas during charging which is a plus.
They are extremely light compared to a SLA, but could be used as ballast to eliminate the power cable in the tether.
Regards,
TCIII/SSN626B

[Toffe]

Yes Steve, that is why i redesigned it to the one you made there. I really like the simplicity of that design.

The only problem i have is that i dont have a lathe so i cant machine that out Nor the materials. I'll have to check, please come back with pictures, ideas and more! I have been waiting and waiting for a idea for the motors so i can get my ROV flying as soon as possible!

[sthone]

Ok I've put this off long enough.... let the construction begin.

mdhousing001.jpg (975.06 KiB) Viewed 6929 times

I started by cutting of a 4" piece of the 2" PVC Rod on my bandsaw.

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Next that gets centered in a 4" 4 jaw chuck on the lathe.

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Then a few quick cuts to clean up the face.

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After that I use a few different drills to make a hole for my boring bar.

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I then bored a hole in the piece leaving about a 1/4" for wall thickness. Everything is pretty much done using the TLAR method (That Looks About Right) at this point.

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I had to put a step on the inside edge to allow for a little more room for my internal threading tool as it isn't quite long enough to thread as deep as I would have liked.

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Next I mount up the internal threading tool in the tool holder and hope for the best. (I haven't cut threads in a long time.)

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I chose to go with a 18tpi thread for the motor mount. This is done but adding the right gear ratio to the lathe.

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After the first pass I check the cut with a thread gauge to make sure everything is setup correctly.

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They need a little clean up but here are the internal threads for the adjustable mounter mount.

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Next I turn down the outer edge for the threads for the rear cap.

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This time using a extenal threading bit a cut the cap threads.

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So far this is what I have for the rear section of the thruster housing.

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At this point I've removed more material than I have left, but that's machining for you....

[thegadgetguy]

Awesome! I can not wait to see the rest.

[Bubbles]

Nice design!My opinion is to replace if possible one bearing (the one close to the end cap)with a thrust bearing.Its better for axial load and the cone would rotate better.I have a similar design thruster and when I replace one bearing with a thrust one the rotation is much better.