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Magnetic bindings

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rynhardt
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Magnetic bindings

Postby rynhardt » Fri Jul 10, 2015 12:15 pm

I was wondering... how awesome would it be to have magnetic bindings, as opposed to footstraps or boots.

Basically have enough binding force to keep the board attached to your feet during jumps and rotations, but also be able to release when you dig in an edge.

Surprisingly enough, Google didn't return much in terms of existing wake/kite applications.

So, best way to find out is to build it and see!
Let the madness begin!

The thought process:

The binding should keep the board attached during jumps and rotations - so, a fairly strong magnet and metal plate combination is needed.
But the binding should release when things go wrong - therefore not too strong.

It should allow strong lateral forces for steering and rotations, which implies some kind of lateral engagement lock is needed.
Once again it must release under severe loads to avoid joint injury if only one foot releases.

Should be able to walk/swim in bindings if necessary. So the magnet cannot attach to the shoe, otherwise you'll pick up any metal on the beach.
Which implies that the magnets need to attach to the board.

But the board should still transport easily, which means the magnets can not attach to the board permanently, so a bracket of sorts is required.
And the system should fit my existing boards, therefore the bracket must bolt onto standard 6" spaced inserts.

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rynhardt
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Re: Magnetic bindings

Postby rynhardt » Fri Jul 10, 2015 12:15 pm

Which brings me to the initial design spec:

Magnet:
44mm dia x 6mm high Neodymium disc magnet, sourced locally.
Holding force initially unknown, but pretty strong. Later established empirically at around 7.5kg in the final application.

Bracket:
175mm long x 50mm wide, with 8mm high cap to hold the magnet. 6mm holes drilled 6" apart for mounting.
The cap serves to locate the boots as well as transfer lateral forces for steering.
The sides of the cap are bevelled to cam out when excessive force is applied.
Non-magnetic material required, so I used carbon fibre. Which also looks good.

Boots:
A pair of cheap ankle high sneakers, with 50mm dia x 6mm deep locating holes drilled in the centre of the soles.
A 100mm x 60mm x 2mm metal plate glued into each sole, with inner sole glued over for comfort.
The plate covers enough of the sole to not rip out easily, but can still bend at the toe joints for comfortable walking.

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rynhardt
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Re: Magnetic bindings

Postby rynhardt » Fri Jul 10, 2015 12:18 pm

Bracket:

Decided to build a mould for the bracket. I love using moulds.
For the plug I fashioned a bevelled cap 44mm dia (top) and 50mm dia (bottom), 8mm high, from acrylic sheet.
Solvent welded this to another acrylic sheet and the plug was done.

Wax, release agent, gel coat, fibreglass reinforcement, MDF backing and more fibreglass to finish the mould. Cure and high-temp post cure.
Clean up and wax a few times. Apply release agent. Mould ready.

I will use the plug as the mould negative (very convenient). Wax, release agent - ready.

Layup: two layers of 250gsm carbon twill with a layer of 400gsm 45 deg glass biax inbetween. Nice to finally use up some old scraps.

Clamp the mould and plug together. Cure and high-temp post cure. Et viola! First bracket released nicely.
Finish up the final shape with a cutting disk. Drill holes.
Bracket done.
Attachments
Plug and mould.JPG
Bracket.JPG
Bracket and magnet.JPG

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rynhardt
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Re: Magnetic bindings

Postby rynhardt » Fri Jul 10, 2015 12:20 pm

Boots:

Go buy a pair of el cheapo $20 sneakers. Remove the inner sole and base. Drill a 50mm hole in the centre of the sole.
Fashioned a suitably shaped plate from 2mm steel plate I had lying around.
Epoxy the plate into the shoe, epoxy base and inner sole over plate. Leave to cure. Clean up.
Boots done.
Attachments
Metal plates.JPG
Finished shoes.JPG

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rynhardt
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Re: Magnetic bindings

Postby rynhardt » Fri Jul 10, 2015 12:23 pm

Testing - dry run:

Place magnet inside bracket, screw bracket onto piece of wood. Attach weight to piece of wood. Place sneaker onto bracket and lift!

1st run: 5kg weight. Easy peasy.
2nd run: 10kg weight. Nope.
3rd run: 7.5kg weight. Possible if you're careful to keep the shoe and bracket aligned.


So far I'm pretty happy with the results. Going to make another bracket to complete the system for one board in the next week or two.

Wet run testing will have to wait for September when the season opens..

Stoked!

Short, crappy video of testing:

https://vimeo.com/133015603
Attachments
Bracket and boot.JPG
Test rig.JPG
Lifting weight.JPG

BWD
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Re: Magnetic bindings

Postby BWD » Fri Jul 10, 2015 2:31 pm

Wow, you are making a perennial joke into a reality!
Maybe not such a bad idea, could be really cool if it works.
Corrosion will be your enemy. Maybe some kind of thin encapsulation will be needed.
Balance this against the magnet's needed proximity to the boot plate...
I might think you'd want a non-round (rectangular?) bracket to help transferring yaw moments etc without your feet pivoting or maybe a non-magnetized heel cup bracket to grab the shoe heel?
But I wonder if your joints would be less or more stressed by having freedom to rotate fee on the magnet.?? Maybe this is par of the idea?
Just throwing out some thoughts ...
Keep it up and best luck with the project!

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Laughingman
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Re: Magnetic bindings

Postby Laughingman » Fri Jul 10, 2015 3:16 pm

Not only good for kiting, if you lose your keys in the sand you can drag your board around the beach to find them.
lol

No but seriously, I thought it was a joke to start with as well... the best thing is that you actually have the skills to make it reality.
We use rare earth magnets everyday at my work, very useful but they do have a tendency to break down over time, so you will definitely want to seal the magnet once you have perfected your design. When they break down the edges can be razor sharp....

chrislandy
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Re: Magnetic bindings

Postby chrislandy » Fri Jul 10, 2015 3:29 pm

Interesting concept, I would think 7.5kg is no where near enough though, come down hard on the tail and your front foot will probably release, I'd be thinking at least two or three of those magnets per boot? - any more and I would have thought you would have trouble disconnecting your foot from the board.

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rynhardt
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Re: Magnetic bindings

Postby rynhardt » Sat Jul 11, 2015 4:21 pm

@BWD: I thought specifically to keep it round to allow some freedom of movement.

@Laughingman: Not only good for finding keys.. Also no roof rack required :-)

@chrislandy: You're right 7.5kg is not nearly enough.


Anyway, I did mount it to one of my boards and it really is much too weak to remain attached whem doing any kind of jumping.

Bummer. :-?

I reckon you would need to be able to lift at least 50kg to make it strong enough to be useful.
Even if I could get a strong enough magnet it would be somewhat dangerous to have that much magnet around anything else I own. :o

So, net result is a failure. But at least I tried and now I know...

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Re: Magnetic bindings

Postby randycasburn » Sat Jul 11, 2015 5:02 pm

@rynhardt - It is people like you that make the world go round! I applaud your ingenuity.


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