Magnetic coupling


#1

Obviously way off price and too low a torque, but maybe some interesting ideas here for this 48v system : Magnetic coupling 10kg thrust


#2

Hi @philgib,
I think you are on to something here. I’ve been doing my own research into making my own magnetic driver system. they seem fairly straight forward to make if of-course you have access to a 3D printer.
There are a number of electric outboards that run a sealed motor and pretty much most pumps these days run the same.
I don’t have the models created yet - but basically on the motor side there’s a drum around 60mm dia containing 8 of these magnets… https://www.first4magnets.com/rectangular-magnets-c35/30-x-15-x-5mm-thick-black-epoxy-coated-n42-neodymium-magnet-10-1kg-pull-p4135#ps_1-4336 …… arranged longitudinally around the circumference alternating between North & South facing outwards. The prop fits over this with a similar number of magnets inside.
Each magnet has the strength of 10kg…… I believe the shear value is around 60% of that. If my understanding is correct then the ‘grab’ of those magnets is significantly higher.
Right now I’m researching whether, theoretically at least the prop can be held in place by magnates alone. If it’s possible then not only can the motor be completely sealed but bearings are eliminated in the prop making for a super-simple yet efficient drive unit.
In the outboard world props appear to be running at between 2000 and 3000 rpm depending on manufacture, HP and whether the motor is 4 stroke or 2.
FYI – I intend to use an 80mm dia 6KW inrunner Alien Power is bringing out later this month.
I’d be more than happy to work with you to bounce ideas off and share research.


#3

Great, this is all about bouncing ideas indeed. I have work intensively with building flying drones for the last 5 years, and I know how fragile electronic is, above all in salted water.

So having a waterproof chamber for the motor would be really excellent and a real peace of mind !


#4

As soon as I have something - will let you know


#5

Hi @philgib,
Further research and a tel call leads me to these magnets -
https://www.first4magnets.com/circular-ring-magnets-c37/30mm-o-d-x-10mm-i-d-x-10mm-thick-diametrically-magnetised-n42-neodymium-ring-magnet-p3691#ps_1-1959
Guy on phone reckons each magnet has around 15Kg pull strength. They are designed very much with magnetic drives in mind. Because there is both North and South acting at the ends this essentially doubles the rotational force - though this reduces over the air gap. With these in mind I think the gap between them will need to be around 4mm - i.e. 2x1mm air gaps or clearance plus 2mm for the plastic case.
At 30mm dia these are pretty compact. I’ve gone ahead and ordered a couple. Will put them together next week and let you know how it all works.


#6

I also love the magnetic coupling idea though I know nothing about the phisical limitations. this is a nice simple overview:
https://www.kjmagnetics.com/blog.asp?p=magnetic-coupling


#7

How is this progressing?

I’ve tried doing some rough calculations to mock this up, as I was aiming for better water separation and I don’t think this is going to work, but I’m happy to be proven wrong. Please tell me where I’ve fucked up.

I’d imagine we would need a minimum 3mm gap between them (2mm case + 1mm airgap). Using for arguments sake a neodymium N38 25x5mm disc (nominal ~10kg of pull force), the actual force generated magnetic to magnet with this gap is closer to 3kg.

Once the shear force of rotation is taken into account, I don’t think we can get sufficient magnets within the diameter for the 58mm tubing to work, I think we’ll get slip.

Happy to be wrong!

refs: https://www.kjmagnetics.com/calculator.asp