Solar powered toy/mobile

[Nick]

My mother gave us a solar powered mobile when our daughter was born. Originally table/desk mounted, I slightly converted it and screwed it to the ceiling above our kitchen table (that's the DIY bit). Kept infant daughter amused for hours. 4 little planes spinning around and glittering. Solar panel, on S facing window, is about 2 Sq Ins.

Watching it today in a quiet moment whilst having a cuppa and reading the daily rag. It's doing about 50rpm. Yes, I did count. That got me to thinking. Some winter days it does not turn at all. Mid-summer it can be going for

8-10 hours. Say an average of 1hr for each day of the year. No.1 daughter was 34 yo last month. That equates to about 36 million revs of this little thing.

It's not particularly nicely made and gets only sporadic maintenance (dusting off and a drop of 5W to the plain bearings). I am amazed that it has been so phenomenally reliable Would be interested to know if such are still available. Both our daughter and our son, with his wife's loving assistance, have awarded us with grandchildren recently.

Perhaps I should get out more. Thanks, Nick.

[Brian Gaff]

I used to have some solar powered plant turners, which were special gifts from CPC from way back. Apparently some of these are still going 30 years later.

I've not seen the one you mention, but I'd have thought these might be available from those shops who sell kiddie related stuff, no doubt at a huge mark up.

Pound shops or some little Asian corner shops might be worth a look, or of course the ubiquitous Internet. Brian

[Martin Brown]

Not seen the one you describe but this one certainly is:

And you could probably hang whatever lightweight contraption you wanted instead of the crystal.

[Johnny B Good]

Intrigued, I decided to compare it against a bit of tech that I'm fairly well acquainted with, the humble hard disk drive, typically, the desktop drives that spin at 7200rpm (other rpms are available) with the manufacturers typically claiming MTBF figures anywhere from 300,000 to

1,000,000 hours (not to be confused with the more meaningful MTTF statistics usually specified as a percentage of failures per year - typically ranging from 0.5 to 10 percent or higher).

Now, a hard disk drive is a very complex electromechanical device where a failure anywhere within this complex system can mean total failure hence the apparent discrepancy between an average lifetime of 300,000 hours spin time (just over 34 years) implied by the lower MTBF figure and the more likely lifetime of 3 to 6 years experienced by end users using the more reliable brands.

One thing is clear though, in order to claim MTBF figures of 300,000 hours and greater, the manufacturer must be expecting the platter spindle bearings to *at least* manage to survive long enough to achieve that quoted MTBF hours figure (there's plenty of other 'stuff' in a drive to... well, "stuff up" to account for the more likely 30,000 hours MTTF experienced by the end consumer).

With all that in mind, I calculated a conservative lifetime in terms of a total RPM figure of 129,600 million revolutions on average. That's almost 4,000 times the figure you quoted for that solar powered mobile. Impressive a figure as 36 million revolutions is on a low tech "toy", you need to put it into perspective as to what has been possible for the past

30 or so years on what is now a mass produced piece of high tech kit (the HDD manufacturers have been quoting half million hour MTBF figures from the mid eighties onwards).

One final consideration is the fact that the observed 50rpm is a mere

0.7% of the 7,200rpm example disk drive which vastly improves the life of the spindle bearings of that mobile expressed in terms of a total revolutions count. Despite its very low technical quality, given enough TLC by yourself and the succeeding generations, your great great great grandchildren could well find themselves lumbered with continuing "The family Tradition" (or the motor could just simply wear out next week).

[damduck-egg]

Garden centers stock very similar items . Bees, and Butterflies flying around in circles.

G.Harman

[Bob Eager]

Finally remembered what they are called. A Crookes radiometer.

Rapid sell them!

[T i m]

Unless I've missed something on this thread I've got one of those on the window sill in front of me but I don't think that was what the OP was describing (as it's in a vacuum and therefore you couldn't access the bearings for lubrication and doesn't have a remote solar panel)?

For some reason I thought what I have was called something else but maybe it was just 'Radiometer'.

I visualise the OP talking something more like (but not) this:

Cheers, T i m

[Chris Hogg]

For all sorts of reasons, I don't think that the OP is describing a Crookes radiometer. The OP mentions a solar panel, which suggests it's got a little electric motor in it, and it's something like this

The flex is to power a light bulb in case there's no sunshine. Perhaps all the solar farms and people like Harry with roof panels could use the idea! :-).

The OP may see something here

, in which case he can click on the image and maybe follow it to a point of sale. Or there's lots of solar powered toys here, if he can't find exactly what he wants

[T i m]

I think this would be harrys idea of heaven:

If it's sunny then you get a nice breeze and if it's dark but windy you get sunshine ... ;-)

Well, I know we use electricity from the grid to keep wind turbines spinning so the above should also make equal sense?

Cheers, T i m

[Vir Campestris]

I saw one of those in a shop window once. With a halogen lamp shining on the cell!

The ones I've seen that do make sense are the little fans powered by a thermopile. You park them on top of your wood burning stove, and they blow the hot air around the room.

Andy