
Inertial Locking Box (2013) - luu
http://www.tessmyers.com/inertiabox.html
======
nickcw
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 :-)

~~~
enriquto
> 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.

------
nimbius
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...](https://me-
mechanicalengineering.com/governor-types-centrifugal-governor-and-inertia-
governor/)

~~~
jamesakirk
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...](https://archive.org/details/CyberneticsOrCommunicationAndControlInTheAnimalAndTheMachineNorbertWiener))

~~~
jhayward
> _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.

------
OnACoffeeBreak
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](https://www.felixure.com/product-page/titan)

2:
[https://www.youtube.com/watch?v=P4naYABpS5s](https://www.youtube.com/watch?v=P4naYABpS5s)

------
roland35
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...](https://www.inetres.com/gp/military/infantry/grenade/40mm_ammo.html)

~~~
Animats
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.

------
tromp
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/](https://www.instructables.com/id/Wooden-Centrifugal-Puzzle/)

------
yetihehe
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.

------
sdoering
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.

------
kazinator
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://en.wikipedia.org/wiki/Ignition_timing#Mechanical_timing_advance)

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

------
praptak
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.

------
tlrobinson
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.

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

~~~
tlrobinson
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.

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

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

------
blfr
Is there a video?

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

~~~
finnh
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)

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

~~~
TessMyers
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.

