

Lava Lamp Centrifuge - jballanc
http://neil.fraser.name/hardware/centrifuge/

======
hga
_Extremely_ cool:

" _The centrifuge is a genuinely terrifying device. The lights dim when it is
switched on. A strong wind is produced as the centrifuge induces a cyclone in
the room. The smell of boiling insulation emanates from the overloaded 25 amp
cables. If not perfectly adjusted and lubricated, it will shred the teeth off
solid brass gears in under a second. Runs were conducted from the relative
safety of the next room while peeking through a crack in the door._ "

Read the rest to learn if a lava lamp will work on Jupiter or during a space
shuttle launch (2.3 or 3 Gs).

~~~
mikepurvis
My team's washing machine prototype achieves 200+ Gs in the spin cycle.

There are some problems in this video that have since been corrected, but
check it out: <http://www.youtube.com/watch?v=mK2vpqXk8Jc>

~~~
Groxx
haha, that's awesome. Is there a goal to this project aside from epic-spin-
dry? I'd love to see where it's headed.

~~~
mikepurvis
It loads through the side of the drum, rather than the end—this addresses two
major mechanical sore-spots in traditional front-load washers (which are
otherwise vastly superior to top loaders).

It's not an entirely new concept (cf. <http://www.staber.com/>), but our
approach to the door and very ingenious and novel.

------
ars
If you plan to make one, make the radius smaller, but the velocity higher.

The energy stored in this goes by the radius squared. But the centripetal
force on the object at the end goes by the radius.

So a smaller faster one is less dangerous, and also requires a less powerful
motor (or the motor you have can give you a higher force).

Although the bearings are probably a bit harder to handle when it's faster,
the whole thing will weigh less.

On the con side, a smaller one will have a larger difference in force between
the top and bottom of the lava lamp, making your experiment less accurate.

~~~
Groxx
Energy may go by radius squared, but the rpms change to match.

For visualization: the ice-skater who spins slowly & pulls arms in. By
spinning faster, no energy is _lost_ , as can be seen by extending the arms.
However, a slower-rotating device can more easily be predicted and avoided /
hand-stopped if needed.

~~~
rbanffy
The energy is the same. A slower moving larger centrifuge can tear your arm
off with the same ease a smaller, faster one.

~~~
Groxx
Totally agree. But a smaller, faster one is less predictable, so you can't
bleed of small amounts of energy as easily / safely.

Which would you rather try to stop, with your bare hands, assuming identical
energy? A 1-inch pipe spinning at 10,000 RPM, or a large tire spinning at 10?

~~~
ars
If the energy is identical, why would there be any difference?

Remember that with the larger slower RPM one, the radius is higher so the
linear velocity is high too, even if the RPMs are slow.

~~~
Groxx
One is more predictable than the other. In that video, I can point out when
the arm will come around again with relative ease, and can very easily be
accurate to below a tenth of a second.

Now picture it going several times faster in terms of RPM, and tell me when
it'd be safe to stick your arm in its path.

Lets scale it up. Picture the earth. Near the equator, the linear velocity is
almost 1000mph. Scale it down to the size of the centrifuge in the video,
while keeping linear velocity the same. I can easily point out when half of
the earth is facing the sun. Could you point out when the centrifuge is
pointing north?

~~~
ars
If you are planning to play chicken with a centrifuge, sure.

But I am more concerned with what happens if you do actually get hit. Or if it
comes apart, or falls down.

And if you do get hit, or it breaks, a smaller faster one is MUCH
(exponentially much) safer.

The force goes up by the RPM squared, but it goes down only linearly by
radius. You don't need to speed it up very much to counteract the smaller
size.

On the other hand the energy goes up by radius squared. Meaning the smaller
size helps a LOT in terms of destructive power.

~~~
Groxx
I've been too long out of physics, so I'll take your word on it. I wasn't sure
how quickly size effected energy. Though I'll still take my chances with
something I can predict if I have to interact with it.

One question though: is energy->radius^2 based on angular or linear velocity?

~~~
ars
Angular.

So yes, when you increase the radius the linear velocity goes up even though
the angular one doesn't change.

------
johnohara
No wonder landlords ask for a security deposit.

------
Groxx
I _love_ that the "data recorders" are a cell phone and a camera.

This is awesome. _Everybody_ should do something this awesome in their
lifetime.

edit: Yikes, anyone got a torrent / mirror for those videos? They're crawling
at sub-30kbps for me.

~~~
Groxx
Well, if anyone's interested, these links should work in a bit over an hour
(or two... fluctuating speed), provided it all downloaded correctly (I'm
headed to sleep). Don't try before then, they won't be complete, I'm just
downloading to my Dropbox.

<http://dl.dropbox.com/u/363028/temporary/3g-side.3gp> (16mb)

<http://dl.dropbox.com/u/363028/temporary/3g-floor.avi> (159mb)

<http://dl.dropbox.com/u/363028/temporary/3g-payload.avi> (43mb)

Please mirror / set up a torrent if you can, I'd prefer to not nail my Dropbox
too hard. (payload is interesting, you can see the twisting caused by the
spinning)

~~~
dasil003
Dropbox will shut you off without warning. I had a 25mb training video up
there for a 15-person startup and my public folder was turned off
astonishingly quickly.

~~~
Groxx
Good to know. And makes sense, as they truly aren't providing a CDN.

------
dasil003
Upon clicking the AVI video links in Safari I discovered that the QuickTime
logo is strangely reminiscent of a centrifuge.
[http://skitch.com/dasil003/n292m/http-neil.fraser.name-
hardw...](http://skitch.com/dasil003/n292m/http-neil.fraser.name-hardware-
centrifuge-3g-payload.avi)

------
pook
I wouldn't be concerned so much with glass shrapnel, as with almost molten wax
spraying out.

Have you ever opened up a lava lamp? The bottle is capped with an old-
fashioned pull-off bottle cap. I guarantee that if anything goes pearshaped,
it'll be the integrity of that cap.

------
arethuza
I want to see the videos of the failure mode testing :-)

------
flipbrad
could an engineer/physicist be kind enough to calculate how hard that lamp
would have hit the nice wall, door or window had things gone a little awry?

~~~
ars
He says it has a diameter of 3 meters, and spins at 42 RPM. (And I hope he
didn't confuse diameter and radius.)

So the circumference is 9.5 meters, times 42 per minute = 395.6 meters per
minute = 14.76 mph or 23.75 km/h
[http://www.wolframalpha.com/input/?i=3+meters+*+Pi+*+42%2Fmi...](http://www.wolframalpha.com/input/?i=3+meters+*+Pi+*+42%2Fminute)

------
pinstriped_dude
The music is cool and the "study" room setup is endearing. But, in plain
English, what's the result of the experiment ?!

~~~
brisance
"As one can see in the video above, the lava lamp continues to operate well at
three times the force of gravity."

~~~
Groxx
As well as "IT LIIIIIIIVES!!!!" when you get it spinning for the first time,
and scaring / awesome-ing the neighbor kids.

What the heck is that thing made of, anyway? An erector set? Juice bottles?
Over-powered wires and motors? That beast is _worthy_ of a Frankenstein
moment.

~~~
ars
It's made of <http://en.wikipedia.org/wiki/Meccano>

~~~
Groxx
So, pretty much yeah, an erector set, though possibly a bit stronger. It's not
old-school erector, though. Looks like Meccano has been making Erector sets
since about 1990.

------
bluedanieru
Well, that's one less thing to worry about.

