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See, I'm a low-g cargo shipper by trade. We get all sorts of containers in all kinds of shapes that we need to fasten to the deck plating, and to do that we use magnetic clamps.

Now, these clamps are all manner of strong. Like, stupid strong. My engineer tried to explain it to me, something about super magnetic rare earth, I dunno. When the power is on we can just deactivate the clamps, but when the clamps lose power they snap back to the deck like a bear trap to a grizzly. Makes sense, I guess, cos the last thing you need when the reactor cuts out midway to Europa is two ton metal boxes floating about the place.

Thing I can't figure is how they work!


The question here is what effect or mechanism could be used to negate the effect of a very powerful solid state magnet if and only if power is available. Simple designs are preferable.

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  • $\begingroup$ These exist in a slightly smaller fashion, but I think you could scale it up: en.m.wikipedia.org/wiki/Magnetic_base $\endgroup$ – sdfgeoff Sep 18 '17 at 13:41
  • $\begingroup$ @sdfgeoff : Put that in an answer!! The fact that that bit of genius exists already is brilliant. $\endgroup$ – Joe Bloggs Sep 18 '17 at 13:47
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These already exist, and are called Magnetic Bases. They are used for attaching tools onto workshop equipment: enter image description here

They attach very solidly (Nearly impossible to remove by hand), and I think that if they were upscaled they could indeed work for holding containers onto spacecraft. They can clamp any piece of ferrous metal.

As they currently are designed, they do not require any power to hold in either the on or the off position, and the force required to toggle them is tiny compared to the force they can exert. If you want them to automatically engage when power is not applied, then the addition of a rotary spring to auto-rotate the magnet into the "on" position should allow this.

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  • $\begingroup$ Wish I could upvote more than once. Not only is this exactly what I was looking for (with a small extra spring and magnet assembly to toggle the states automatically) but it's simple enough that I could have a go at machining my own. $\endgroup$ – Joe Bloggs Sep 18 '17 at 16:12
  • $\begingroup$ As the person who asked the question, you can make the answer as "Accepted" which will highlight it for future visitors. $\endgroup$ – sdfgeoff Sep 18 '17 at 16:30
  • $\begingroup$ I'm aware. This isn't my first zero g magnetic clamp rodeo. I'm waiting a while to see if any other answers come up. I doubt a more suitable one will, but still. $\endgroup$ – Joe Bloggs Sep 18 '17 at 16:53
  • $\begingroup$ Oops, should have looked at your rep before posting that. $\endgroup$ – sdfgeoff Sep 18 '17 at 20:03
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    $\begingroup$ I'm looking for drawbacks compared to my above proposal, but can't find them ... ;-) $\endgroup$ – Karl Sep 18 '17 at 20:49
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Simple:

One bar magnet on the cargo, fixed, one in the floor, that can rotate freely. Without power, the two align north to south, south to north, and hold the cargo in place.

There is a motor connected to the floor magnet with a clutch that is closed by a small electromagnet. The motor can turn the floor magnet until the net force is zero. There is still a large torque on the magnet then, so in a power failure it will snap back immediately.

During loading, the floor magnets are monitored by a feedback loop that always turns them into the "neutral" position with respect to any passing cargo magnet fixture. The magnet on the cargo can move vertically slightly and is kept fixed in the "away" position by a small spring. That way a power failure during loading is less dangerous for the workers feet, and you don't get large torques on the cargo.

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  • $\begingroup$ sweeeeet! That would work! $\endgroup$ – Willk Sep 18 '17 at 0:06
  • $\begingroup$ The other awesome thing about this is that no power at all is needed, ever. I was thinking about electromagnets with their own batteries but those could run out, or fall afoul of an emp pulse. The @Karl system will hold that cargo for hundreds of years. $\endgroup$ – Willk Sep 18 '17 at 1:30
  • $\begingroup$ Could this de-magnetize the clamps after excessive use? I'm not an expert on magnets but an opposite magnetic field of sufficient strength should realign some particles in the magnets. $\endgroup$ – Braydon Sep 18 '17 at 5:26
  • $\begingroup$ Hadn't considered rotating the magnets at all, and the clutch makes snapping back nice and simple. Only downside is this requires the system to be installed in both container and ship. +1 $\endgroup$ – Joe Bloggs Sep 18 '17 at 6:36
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    $\begingroup$ @Braydon They must de-magnetise eventually. That's a physical law, a permanent magnet is only thermodynamically stable if kept in a magnetic field. However with modern rare-earth magnets it will take longer than the lifetime of the universe. Was a problem with cheap old Alnico magnets, you always had to stick them to a piece of iron or they would demagnetise over a few years. Or so they said. $\endgroup$ – Karl Sep 18 '17 at 6:45
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Distance.

Each clamp is its own independent system, essentially a very powerful permanent magnets sandwiched in the middle of two screw driven scissor lift assemblies. Each screw is driven by a high speed electric motor, which also has an attached battery that always maintains enough charge to lower the jack to the floor.

Operation is simple: plug power into the jack motors and raise them to their full extent; this will pull the magnet away from whatever surface it was attached to. Move the clamp to the desired container and wind down one of the jacks, bringing the magnet into close proximity (or if the clamps are made right direct contact) with a magnet. Move the container to its desired location and lower the second jack, bringing the magnet into contact with the deck.

To release cargo just extend the first set of jacks again. There will still be a little magnetic pull, but due to the distance from the magnet the cargo should now be free.

In case of external power loss each clamp defaults to both jacks retracted, and the slight magnetic pull of the clamps will ensure the cargo attaches securely to the floor unless the ship is under thrust, in which case why the hell is the cargo not secure already?

Pros: easy to use and repair/replace, works on any ferrous item or surface, can be used to clamp containers together, can be manually operated if required, keeps enough distance between container and floor that crush injuries can be avoided.

Cons: 'snaps' to deck comparatively slowly, takes up space in cargo hold with an air gap, reduces surface area on the deck (and thus frictional forces), won't return to the locked position in case of catastrophic electrical event (i.e. Component failure or EMP)

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