Building a Magnetic Coupled Thruster.

[sthone]

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Thanks Ross that's why I still run the site after all these years... to inspire others. As far as my shop goes I'm fortunate to be setup in a basement where its always about 65 degrees all year so I no longer have to worry to much about rust. I try to keep it clean but it does get out of hand at times with so many things going at once. Above is my current setup (I should update my shop thread one of these days I guess) as usual bench top space is hard to find I have a new toy coming this week so I might have to clean a bit more to make some more room. Anyway back to the fun stuff....

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Onto the prop rotor. I start with another chuck of PVC, face it and drill a 23/64" hole in the end.

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Using a 23/64" Transfer punch to center the other rotor I transfer the magnet locations using a 1/4" punch. (I later noticed the rotor is backwards from what it should be but the holes should still be close enough for the prototype.)

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Now that I have my magnet locations I can start boring the piece out to mate with the cap.

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I start by measuring the depth needed for the bearings.

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I first drilled a 31/64" hole and then bored that out to .50" to a depth of 1.45" to fit both bearings.

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Next I measure for the new thrust bearing washer I made. (I didn't show making this)

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Then I bored out .620" to a depth of .890"

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Next I bored out to clear the step on the cap.

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I tested out the thrust bearing by spinning the piece in the lathe and just holding the cap against it. It seemed to work well at this stage.

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Next I transferred the workpiece over to the lathe and plunged cut the magnet holes.

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After that it was back over to the lathe to drill and tap for the 4mm screw for the prop.

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Next I had to setup the angle on the compound slide to turn the cone shape.

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After a bunch of cutting this is how it looks. I was off a bit with my measurements so I'll have to clean the step up at the end later on.

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I quick test fit reveals it's a tad bit wobbly but it spins very freely. Next I have to glue the magnets in and go from there.

-Steve

[sthone]

After a little hiatus I'm back at it........

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...at this point I've glued in the magnets and after a few quick spin up tests everything seems like its working pretty good so far. It's a tad bit wobbly but better than I expected. Next it's on to the end cap.

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I first face off the back of the end cap and knock off the corner a bit to reduce the sharp edge.

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Flipping the piece in the chuck I start a hole with an endmill so I can fit my boring bar in there.

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I then bored out a section to almost the end of the cap to make room for the motors wires. I left the end cap a little longer than I needed because this is my last piece of material and if a screw up the threads I can just cut them off and try again without having to order more stock and redo the entire cap.

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Next I measure my major diameter of the threads on the housing....

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....after subtracting for the depth of the threads I finish boring out the cap to around 1.73".

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Using my internal threading bit I give the cap its threads and hope for the best.

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A quick test fit and it seems I actually measure right.

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Here is the almost finished end cap next to the housing.

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At this point the thruster is pretty much complete with the exception of the exits for the motor wires.

To be continued.....

-Steve

[kendelrio]

Outstanding jorb! When (if) I ever get around to building my own, I may go with this setup.


Quick question: What depth is your housing rated to? You could go much deeper if you have your thruster in an oil filled housing. We use a dialectric oil on our motors with a positive compensation system (very easy to build, I may post a thread on it when I get a minute to write it up) and can dive up to 15,000 feet with no implosion worries.

Let me know if there is any interest in it please.

Again, great job! I wish I had your shop at home!

[sthone]

Ken, my housing hasn't been rated, this is more or less just a prototype to see if the concept works.

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Next it is on to the through hull connectors. I start with a piece of .25" brass and turn the front down to .20"

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After that using a 12-24 die I thread the piece.

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Then a .1406 hole gets drilled in the end. These are where the motors connectors will plug in.

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Using the parting tool the piece is then cut off.

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The piece is then rechucked in the lathe and I turn down a small step and then drill a .1094" hole in the end. The power wires will connect here and the step is for a bit of heat shrink tubing.

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Here are the three finished connectors and a quick test to make sure the motor plug fits securely.

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After that I drill and trap three holes in the end cap for the connectors.

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The connectors get a bit of Teflon tape and are started by hand.

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Next I protect the connector with a piece of soda can and I tighten them with a pair of pliers.

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So far everything is working out as I had planned.

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Next I soldered the wires right to the connectors. I was going to use a screw on fitting here but to speed things up I went this route for now. (I was a little worried that the heat from soldering would melt the housing but I was quick about it so I think its fine.

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After the wires were connected I added a little heat shrink tubing just to pretty it up. (I'm not really worried about water proofing the connections.)

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Before screwing on the cap I had to pre-twist the motor wires in the opposite direction so when screwing on the actual cap the wires don't twist up and pull free.

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I originally planed on using o-rings to seal the housing but for now I just use more Teflon tape on the threads. (at this point I'm not really concerned about it leaking)

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Well here it is all ready get wet and start some testing.

-Steve

[olegodo]

Really nice work! Looking forward to seeing test results

[sthone]

I got this in the test tub today and while it kind of worked it needs some tweaking. It spins right up but before it can reach full throttle the magnets break away from each other. I might try adjusting the gap and see if that helps but it might just need more magnets. I didn't bother testing the thrust or amps draw because I only was trying to see if the coupler worked. Anyway I'm going to try the gap adjustment first and then go from there.....

-Steve

[a_shorething]

Hi Steve,

Great to see you're back in testing mode.

You might be able to do something with your programming if the change is too abrupt for the magnets to keep up with. Maybe have it set up so that it ramps up instead of going from 0-100% as fast as the input is sent. I know ideally it would be 'locked' together, but it could act as a kind of clutch if you do it right. That would also protect the motor if the prop got stuck on something.

Just a thought.

[sthone]

I think its more just breaking loose because of the drag of the prop at higher speeds. Even if I increase the throttle as slowly as I can it still breaks away before hitting top rpm. The whole protecting the motor aspect encase of a tangling is exactly what I'm going for though. That's why I designed the motor mount to be adjustable so I could dial in the break away force to allow for such things. Hopeful once I add a few magnets it will be strong enough so I can get to that point.

-Steve

[a_shorething]

Very cool, good luck. Looking forward to more progress.

I'm getting back into testing my mag coupler too (finally). Will post in another thread.