h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Apologies if this is too overtly advertising but...

No1Son was in USA a few weeks ago and brought back a Mova Globe.

I find it fascinating. Their website is below but very sparse so far (I'm suspecting it's a very new product). In fact the User manual that came with it tells me more.
http://www.mova.com.au/index.php/products/4-5-mova-globes/

I'll go into a bit of detail in case few of you know about it.

It's a 6" clear plastic globe apparently completely filled with a an inner 'world' globe that rotates when there's enough light (ambient or otherwise).

I can grasp most of the technology but one bit has me headscratching...

There's a stong magnet to interact with earth's magnetic field and they warn that it can be shielded by, eg ironwork girders. This magnet is probably inside the globe at the South Pole and heavy enough to keep the globe 'right' with earth's gravity (you align the outer globe weld with the inner globe's marked equator, manually)

The inner globe is of neutral density with the fluid it floats in - there's no direct contact with the outer globe - it floats in oil "like liquid candlewax".
The world graphic on the surface of the inner globe is about 1/4" from the outer globe but your eye tells you it's completely filled.
The thing is a superb ornament.


Now, I can grasp the above bits but that one aspect: How does it capture light in order to make it rotate - and in the right, eastward direction?


He won't tell me what it cost.

Solar cells.

The Levitating Globe looks pretty cool, too - and a steal at $85.50!

*Not jealous at all*

Interesting. I'm curious now as well. As far as how much it costs, I don't blame your son for keeping quiet. From their, as you said, quite sparse website, a 6" globe is $440. Theoretically, I suppose the globe could have a photovoltaic component which could power an impeller inside the globe that would create a circulation in the fluid that would in turn spin the globe. But this is purely speculation.

Does it spin faster if you have one side in light and the other in dark?

It seems like there should be a Stirling engine inside it. I don't get what the magnet could be for though, stabilization?

Looks like a fascinating bauble.

Always have a problem with globes and maps.
Political maps keep changing.
All the pink bits are shrinking and a lot
of other places keep changing their name.

So I generally prefer geological relief maps.
But they're gonna change eventually too.

Some parts keep crumbling, others being washed
into the sea. Nothing is permanent so it's likely
a better policy to rent or borrow than invest in
the acquisition of a product with a predictable
and built in obsolescence.

And relief maps on a whirled scale really aren't
as lumpy or edgy as you might think. Mountains
that are seven or eight miles high barely register
on a whirled scale of 24,000 miles. But I really dug
the dark blue ocean one without any borders!
It looked like home to me. As seen from space.

BTW:
I have a 15inch lava lamp shaped like a V2 rocket
if anybody wants it.

~jwf~

Yes global warming has obviously been engineered by mapmakers to enable them to keep selling more maps as the coastlines change.

Some of them mountains grow by an inch or two every year.
North America moves westward away from Europe at an alarming rate.
And California is shifting by as much as a foot every time it rains.

~jwf~

>Does it spin faster if you have one side in light and the other in dark?< : Xanatic

No. Any light of sufficiency does it (NOT direct sunlight)
It may be sensitive to brightness but I've not spent the time.
About 20 seconds per revolution - say 25mm/sec compared with 1320 feet...
- -

>I don't get what the magnet could be for though, stabilization?< : Xanagin

Hmm. depends on what shape it is? to start the spin in the right direction?
Correction for S hemisphere? - no, shouldn't need it.
(must see if I can modify it so it's the right way up...)

- -

jwf, I've not had time to check if they've built-in continental drift.

It's not political, the colours are as of nature - forest/desert etc.


Intriguingly, the booklet says it's the first in a series of new thingies...

>> It's not political, the colours are
as of nature - forest/desert etc. <<

That woulda been my choice from the selection
presented of "Products" at the website. (The widest
selection is in the small size and there are only
3 types available in the largest 8.5in model)
There seems to be some selection for the base too
but I'm still at a loss how the thing rotates or
what the magnet does except perhaps to keep it
stable and South side down.

Does it glow in the dark?


~jwf~

Well, my curiosity kicked in and accessed my google-fu.

http://www.worldglobeu.com/university/about/mova/mova-globe-helps

It is indeed photovoltaically powered. They don't go into detail about the drive mechanism, but my guess is the magnet aligns the inernal mechanism with the Earth's magnetic field and the drive spins the globe slowly around it.

A one year warranty...

Would that be one x 365 rotations?

PS: Does no one want my V2 lava lamp?
Can't blame ya; it probably wouldn't
survive shipping or customs.

~jwf~

jwf, The one No1Son brought back is the middle one in the 6" range - 'Satellite with Gold'. Their picture doesn't show it off to best advantage - I'm (very) happy to accept his choice as he has an eye for such things.

This model has the base as shown - sort of leaning tripod. Disturbingly though, only one end of each leg is chamfered & the other is too sharp to be comfortable for standing the globe on - I must take it to the lathe and fix that bit.

- -

Reading through again and after looking at the thing with tightly closed, squidged-up eyes for a while, I'm thinking :

. Yes, must be photovolcaic (:Baron G) - partly, but would that be enough to drive it? (and anyway, How?)

. Xanatic's Stirling engine didn't appeal at first but then it's grown on me - it doesn't have to be vertical?

. The magnet is most likely to be there as a weight to keep the thing North up (sadly)
- also, the magnet will/might provide a little in the way of drive (Baron G).
- also, if suitably shaped, with vanes, would help rotation in a circulating fluid provided by a Stirling Engine.


I'm thinking the three elements above might, just might be enough: magnet plus photovolcaic and (primarily?) Stirling Engine.

Anyway, I shall eMail them & see if they reply...

I doubt it runs on a Stirling engine, a simple electric motor would suffice. Again, I suspect the magnet aligns the internal mechanics with the Earth's magnetic field. A simple electric motor would turn the internal globe around it at a leisurely rate as seen. (BTW? does the North pole point directly up, or at an angle? If it's at an angle, the magnet may be aligned with, or possibly perpendicular to the globe's axis in such a way that the farther North or South it's located will increase the tilt of its axis due to the inclination of flux lines at such latitudes.)

As to the tripod, see if you can remove the two 'legs' that have the un-beveled edges. From the instructions I saw in the link I provided, I believe those two legs have just been inserted into the base upside down. The other ends should have the bevels.

I wonder if it rotates backwards south of the Equator!


~jwf~

Heh, Neil deGrasse Tyson made sure to point out to Jon Stewart the last time he was on The Daily Show that the CGI globe featured in the opening credits is rotating backwards. (The sun would rise in the west.)

Baron Grim, North is directly up and there seems to be no attempt to make it an oblate spheroid. There doesn't seem much point in going to those extents - it's just a decoration and only 6" across.
I'm not clear what you're suggesting about the simple electric motor... whatever drives it is within the inner sphere - I can pick the thing up and rotate it and the inner sphere remains North Up (allowing for jiggle recovery time).

A further point: The thing is a little over half full of that oil, though whether that's the inner sphere, the outer or both I can't tell because of its optical qualities.
Also, there's an axial rod, perhaps 2 or 3 mm diameter. At the South pole there's a similar mark from the sealing process - but nothing at the North. I therefore surmise that the axial rod is within the inner sphere only - and, tentatively, that the oil is in the outer sphere only.

The bevelled legs - sorry, I wasn't very clear: the base is drilled at that suitable angle for a twisted tripod and the three legs came separate, each with one sharp-edged end from being cut off the rod and the other softened with a bevel/chamfer. I'm imagining a process that I sometimes use with wood dowelling:
A long rod through the lathe headstock with suitable length through a collet chuck - tiddly-up the open end & cut off. slacken collet, push another section through, tighten, tiddly, cut off, repeat. Only, they haven't yet thought to finish the job (the raw end is clean-cut but untiddlied). Luckily I noticed it else the outer sphere would be at some risk from the sharp edges.

I've mentioned it to them in an eMail - no reply yet (after 16 hours!).

Incidentally, the eMail was to Australia - they've obviously got (some) regions already set-up with exclusive agents. I could apply to Aus to buy in bulk if I wanted - if anyone is looking for a business opportunity it might be worth looking into. Probably low volume but rewarding (and more trinkets on the way?).


Squigs, NO it blerry doesn't. However, South is down-over thus clearly wrong. Anyway it wouldn't be the 'wrong' way, would it?

Here's how I'm imagining it working. Everything visible is as you've described it. Inside the internal sphere (I'll call this the globe and the outer one the casing) I imagine a framework or chassis for the mechanical parts. I imagine what you describe as the the axial rod will act as an axle for the globe. There are no connections between it and the outer sphere (casing), separated by approx 1/4 inch. I imagine the globe is hollow but ballasted with the internal mechanism and weights to achieve equilibrium in the fluid. On the internal mechanism chassis will be the magnet which will act like a compass needle. It will point to magnetic North and it's perpendicular to the axis/axle. A simple electric clock type motor, powered by the photovoltaics will turn the axis/axle and thus the globe with it whilst the internal chassis, motor and compass needle assembly remains oriented to due magnetic North. The internal mechanism will remain in that orientation even if the outer casing is gently rotated as would say a ship's gimbaled compass.

Anyways, that's how I'd do it.

That's about it as i see it, too, BG.

The globe will be hollow to minimise friction with the oil.

The photovoltaics are presumably laid on as film (inside the globe?)

I said that's 'about' it... at the mo, I'm wrestling with that motor

Hokay, got it, I think (good job I ain't a committee of approval).



Despite all the analysis, it's still exceeding attractive.

I agree, I just don't know if it's $220 - $500 attractive.

Come to think of it... I think the NASA gift shop here on site might have some sort of globes for sale, but I doubt their as nice as these. I'll have to remember to check tomorrow when I go to the cafeteria for ice.