Inertial Locking Box (2013) | Hacker News Reader

Inertial Locking Box (2013)

tessmyers.com

139 pointsluu26 comments

I have a wooden puzzle which you can only get apart by spinning it. It has an internal channel which contains two brass inserts. If you spin the puzzle the brass inserts fly to the ends of the channel and no longer lock the puzzle. Shaking the puzzle or turning it upside down inevitably causes one of the brass inserts to lock the mechanism. It is a good ah ha moment when you figure out that spinning the puzzle unlocks it.

The puzzle in the article works in a completely different way and looks like it is more secure to random fiddling. It looks very attractive too. I'd certainly add it to my puzzle collection if I could :-)

> The puzzle in the article works in a completely different way and looks like it is more secure to random fiddling.

The defect is maybe that it has the shape of a top, so making it turn is a natural thing to do with that object. On the other hand, spinning a wooden cross is much less natural and unlikely to happen by random twiddling.

Sort of related, but old Seagrave firetrucks with 2 cycle, 2 gear engines would use an inertial type governor to lock-out the fuel from the carburetor to prevent overspeed. If you ever see an old engine with a set of weird spinning balls connected to a couple of rods at the top, thats an inertial check. They were also pretty popular with steam engines in factories and saved a lot of lives controlling automatic blow-off valve for over-pressure.

https://me-mechanicalengineering.com/governor-types-centrifu...

Norbert Wiener discussed this in Cybernetics:

"Another example of a purely mechanical feedback system — the one originally treated by Clerk Maxwell — is that of the governor of a steam engine, which serves to regulate its velocity under varying conditions of load. In the original form designed by Watt, it consists of two balls attached to pendulum rods and swinging on opposite sides of a rotating shaft. They are kept down by their own weight or by a spring, and they are swung upward by a centrifugal action dependent on the angular velocity of the shaft. They thus assume a compromise position likewise dependent on the angular velocity. This position is transmitted by other rods to a collar about the shaft, which actuates a member which serves to open the intake valves of the cylinder when the engine slows down and the balls fall, and to close them when the engine speeds up and the balls rise. Notice that the feedback tends to oppose what the system is already doing, and is thus negative. "

(https://archive.org/details/CyberneticsOrCommunicationAndCon...)

> consists of two balls attached to pendulum rods and swinging on opposite sides of a rotating shaft

Random aside: This is the origin of the phrase "balls out" to mean going full-blast. When the locomotive was putting out maximum power the spinning balls on the governor would be furthest out, inscribing their largest circle.

The Titan puzzle by Felix Ure [1] is a brass sphere composed of two hemispheres that slide past each other along the equator. The goal is to unlock the sphere.

I recently watched a video [2] by Mr.Puzzle describing how it is put together (obviously spoiling the solve), and it is incredible!

1: https://www.felixure.com/product-page/titan

2: https://www.youtube.com/watch?v=P4naYABpS5s

This reminds me of the arming fuzes in 40mm grenades. Basically the grenade needs to first be launched, then spun, then delayed some time before the grenade is armed.

The entire system is mechanical and is pretty interesting: https://www.inetres.com/gp/military/infantry/grenade/40mm_am...

i was going to mention Safing and Arming devices too! Apparently there's work going into making MEMS Safing/Arming devices that work like those devices (physically interrupting the explosive train) but are....lots smaller: https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2015/fu...

Yes. That's been the primary arming system for rifled artillery shells since WWI. They have to spin at high RPMs before they arm, something unlikely to happen by accident. Some have to experience the acceleration of firing plus high RPMs to arm.

The Wooden Centrifugal Puzzle [1] is an example of a much simpler puzzle requiring spinning to solve

[1] https://www.instructables.com/id/Wooden-Centrifugal-Puzzle/

Ahh, I remember some bluetooth wmbus reader, which could be powered on or off by shaking it. Presented as puzzle to all new coworkers: "Try to turn it on", so each one proceeded to try rotating antenna or case halves (it was cylindrical in shape), pressing in several places, then shaking near ear to see if something was maybe loose inside, which typically turned it on.

I loved this. When I was doing "Live Action Roleplaying" and organizing events I loved to create locks and puzzles for the players.

This would have been such a great thing to solve for players while being in a dungeon.

Good luck opening it when that nut seizes on the thread.

An alternative design would be something using centrifugal force on some spring-loaded weights, reminiscent of:

https://en.wikipedia.org/wiki/Ignition_timing#Mechanical_tim...

https://duckduckgo.com/?q=distributor+weights&iax=images&ia=...

Tilt indicators are kind of inertial locks used in practice. When tilted over a threshold they lock and indicate that the transport company broke the "do not tilt" spec.

I wonder how far you could take this concept?

A box that only opens under exactly 8Gs of force? Should be easy with an appropriate sized spring and weight.

A box that only opens in zero gravity? Not sure how you'd accomplish that.

Drop it and it will open in free-fall given enough time for the mechanism to react.

For a bonus challenge it should also require some sort of manual manipulation while it's in free-fall. Then your options are pretty much sky diving, in space, or a parabolic flight path.

Do note that falling at terminal velocity is not free fall.

No, but it's generally close enough for most purposes. Especially for a small object with little wind resistance.

For a box to only open in zero G, you could have weighted pins in all 6 directions, pulled back by very weak springs. In normal gravity, whichever pin(s) are "down" will extend and lock it. It would have to be in very low gravity for enough time for the pins to retract to unlock.

Is there a video?

If you turn the whole thing upside down, won't the free-spinning nut work its way along the spindle and unlock the box?

The nut is on a threaded rod, and in the locked state is jammed up against the plate, so it shouldn't work its way anywhere absent rotational force.

(i missed that the rod was threaded in my first read-through, too)

If you sold this, I'd buy it! Patent it and profit.

Similar puzzle was shown when Adam Savage visited Michael from vsauce.

Thanks! I actually did apply to patent the design, but it was rejected based on being a "useful article"( a box) with no non-useful design element that could be copyrighted. Glad to hear that you like the design! It's whacky to see my old work on the front page of HN.

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