longobord at gmail.com
Wed Mar 17 11:48:36 PDT 2010
(Psst. 'reply all' works wonders.)
Thanks Ben for your research. The target we're after is to keep it warm for
5 hours. If the hand warmer only heats to 100F, I think we're also
concerned that it'd be hot enough to keep our stuff warm. The G1 was
measuring -20 on it's internal measure which is heated by battery and the
APRS packet we got through was colder than that.
"We also briefly discussed having officers replaced by very small shell
scripts." -- Noisebridge meeting notes 2008-06-17
The outer bounds is only the beginning.
On Tue, Mar 16, 2010 at 10:49 PM, Ben Rupert <meowdip at gmail.com> wrote:
> Hey, sorry I didn't respond earlier. After talking to Christie on
> Sunday about the heating problems i understand your needs and
> constraints better and have done some research and calculations. I had
> thought about trying to find oxygen in a cartridge similar to the little
> CO2 cartridges used for some BB guns. I couldn't find any that would
> hold enough oxygen in a single unit for a single hand warmer. In fact
> the only ones I could find would take around 5-6. I also considered
> suggesting using a 30% hydrogen peroxide solution instead of compressed
> oxygen (grocery store stuff is 3%). This won't work either as you would
> need about 500g of this solution to burn a single hand warmer. Although
> on the plus side I think I came up with a cleaver and lightweight method
> to introduce the solution at a controlled rate. You could use
> concentrated nitric acid, but you really shouldn't. If it leaked it
> would destroy pretty much anything it came in contact with and might
> also burn through whatever you used to contain the hand warmer.
> The other question though, how long is your flight expected to last?
> Those hand warmers get to just above 100 F, and stay there for up to
> eight hours. If you don't expect to need to heat for that long maybe
> you can just have less oxidant around and let the container collapse at
> the end.
> I'll search some databases at work tomorrow for other reactions which
> might work better as well.
> Christie Dudley wrote:
> > Well, if we're trying to avoid condensation, then we'd actually want to
> > keep stuff above the dew point. Not sure what that would be at that
> > level, and it probably varies depending on clouds, etc.
> > The camera lens would probably be the biggest consumer of heat. It
> > generates no heat itself, has limited insulation opportunity and has
> > significant degradation from cold. Although it doesn't completely stop
> > working, the current theory is that the camera itself stopped because
> > off condensation.
> > I like the idea of a controlled chemical reaction. We'd discussed hand
> > warmers already, but dismissed those because of the need for oxygen,
> > which is obviously limited in that thin atmosphere. I've cc'd Ben
> > Rupert, a recent NB convert who knows quite a lot about chemistry to see
> > if he might be able to help with this discussion.
> > Christie
> > _______
> > "The road of excess leads to the palace of wisdom." -- W. Blake.
> > The outer bounds is only the beginning.
> > http://www.flickr.com/photos/genriel/sets/72157623376093724/
> > On Fri, Feb 12, 2010 at 9:10 AM, Christoph Maier
> > <cm.hardware.software.elsewhere at gmail.com
> > <mailto:cm.hardware.software.elsewhere at gmail.com>> wrote:
> > On Thu, 2010-02-11 at 23:48 -0800, Joachim Pedersen wrote:
> > > So, 555timers are really small ICs, which can't really push that
> > > current, so you would need to have the 555 trigger some kind of
> > > FET methinks. Also, resistive heating is notoriously inefficient...
> > It is, because you lose a lot of heat in the controller, in
> > if you don't use PWM.
> > However ... we want to heat some stuff up to the point where
> > are cozy and warm, not higher.
> > The most efficient way to do this is to use the regulating
> > _themselves_ as heating elements - mounted together with the devices
> > want to heat on a good thermal conductor (i.e., a block of
> > and wrap a good thermal shield (that also serves as padding to
> prevent a
> > reasonably solid piece of metal hitting something at landing) around
> > The electronics would contain power transistors as heating elements,
> > adjustable temperature regulator, e.g.,
> > LM56 or LM57 [ http://www.national.com/cat/index.cgi?i=i//73 ,
> > http://www.national.com/cat/index.cgi?i=i//71 ]
> > and a few resistors and capacitors.
> > Christoph
> > _______________________________________________
> > Space mailing list
> > Space at lists.noisebridge.net <mailto:Space at lists.noisebridge.net>
> > https://www.noisebridge.net/mailman/listinfo/space
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