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Spring Power For Remote Locations

Published : 5th October 2003


Geoff Boyle commented…

>There is a much lower power requirement for 16mm than there is for >any video ormat

I've often wondered what it would take to produce a spring wound accessory motor for the Arri S or the A-Minima. Using negator springs (as in the K100), such a motor would be very light and could probably be made to run for at least 90 seconds. If it could be electronically governed at sync speed (which would use VERY little power -- probably a 9V alkaline battery could do it), that would be fantastic.

J-P, are you there? Is this a completely crazy idea?

Another approach might be a small spring wound, belt-worn generator that charges a small "buffer" battery to stabilize its output voltage. Though much less efficient, it might be a more practical and universal solution, since it could power 16mm and DV cameras as well, and would not have to be sync sensitive. Also, several spring-winds worth of energy could be stored in the battery, allowing longer continuous runs. One of these units could be shooting, while another is being wound up.

(PS: A negator spring is not like the ordinary clock spring you find in most windup cameras. A clock spring is wound in a single spiral; when you wind it up, you simply tighten the spiral. But a negator spring works between two spools. At rest, the spring is wound fully onto one spool. To wind it up, you wind the spring onto the second spool, where it's curled in the opposite direction, thus storing its mechanical energy. In other words, it wants to return to its original spool. The arrangement is roughly like a displacement magazine in which the take-up spool winds the film emulsion-out. This takes up a bit more space than a clock spring, but has several advantages: Unlike a clock spring, its output is extremely uniform from start to finish, so it puts less stress on the speed-governing mechanism. Likewise, winding the spring is very easy and doesn't get harder as you approach full wind. You can pack a lot of run-time into a small negator spring, and I don't think there's any theoretical limit to it.

Do a Google search on <negator spring> to find out more than you ever wanted to know....including an excruciatingly detailed analysis of Abraham Zapruder's 8mm B&H camera!)

Dan Drasin
Producer/DP/Wannabe Boffin
Marin County, CA



Dan Drasin wrote :

>I've often wondered what it would take to produce a spring wound >accessory motor for the Arri S or the A-Minima.

Given that the A-Minima can be run from relatively cheap, tiny, and disposable lithium cells that are tiny and can be purchased at WalMart for about $20/set (and a set is good for 1600-2000 feet) it seems pretty silly to add noise and bulk and mechanical problems to solve a problem that doesn't exist. The weight and space these batteries take up in comparison to the amount of film they'll pull through the camera makes their size and weight and cost truly negligible for remote location shooting. The four batteries end up being slightly bigger than two AA cells.

If you can shoot 2000 feet for $20, that's a penny a foot. Given what stock and processing and transfer/printing costs, that's pretty cheap. And on a long camping trip, the added weight of the food you'd need to carry to cover all the extra calories consumed by all that cranking would probably be worse than the weight and cost of the lithium cells!

Of course, you could just bring a Bolex... and be cranky.

Jeff "and we can bring my spring wind, tube electronic Nagra II" Kreines



>cheap, tiny, and disposable lithium cells that are tiny and can be >purchased at WalMart for about $20/set (and a set is good for 1600->2000 feet)

Hi,

Well, if it takes that little power, it should be possible to run it off one of the wind-up battery replacements which have resulted from the famous wind-up radio, or a solar panel trickle charging batteries.

If you're in the burning desert, solar panels work well. Even a biggish 25-watt one, which would run my video camera without having to accumulate to batteries, is something you could sling over your shoulder and work with the sun to your back!

Phil Rhodes
Video camera/edit
London…where for some unaccountable reason solar panels don't work very well.



Dan Drasin wrote :

> Another approach might be a small spring wound , belt-worn generator

You almost had me interested until this. One of my new years resolutions 2003 : Just say no to battery belts !

Jeff Kreines writes :

>the added weight of the food you'd need to carry to cover all the extra >calories consumed by all that cranking would probably be worse than >the weight and cost of the lithium cells!

Takes a bit of helium out of THAT trial balloon ! But can you back this up with charts, please ?

Sam Wells
Bolex shopping in fact for like reasons.



Sam Wells wrote :

>Takes a bit of helium out of THAT trial balloon ! But can you back this >up with charts, please ?

Walter has them on his web site, I think.

Jeff Kreines

>Walter has them on his web site, I think.

You'll also be able to find them on page 1,432 of the new edition of the ASC manual.

George Hupka
Director/DP, Downstream Pictures
Saskatoon, Canada



Dan Drasin wrote :

>If it could be electronically governed at sync speed (which would use >VERY little power - probably a 9V alkaline battery could do it), that >would be fantastic. J-P, are you there? Is this a completely crazy idea?

Hello Dan,

'negator spring'…yes we considered this idea but it's bulk, weight and noise added to the camera. For remote locations we preferred to make the A-Minima a low power machine able to run from a set of disposable lithium cells (and in the near future out of a fuel-cell).

BTW : you probably would never amortize the cost of a mechanical generator compared to the few lithium cells you will ever burn-out.

Jean-Pierre Beauviala/Aaton
Grenoble France
www.aaton.com



Jean-Pierre wrote :

>BTW : you probably would never amortize the cost of a mechanical >generator compared to the few lithium cells you will ever burn-out

I liked my calorie - to - weight argument better...

Jeff Kreines