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[OM] Reasons *not* to drop your Oly; was: most durable camera discussio

Subject: [OM] Reasons *not* to drop your Oly; was: most durable camera discussion, incl OM-1, from Leica f
From: "John A. Lind" <jlind@xxxxxxxxxxx>
Date: Wed, 28 Jul 1999 12:57:42 +0000
Reasons you do *not* want to drop your Oly (or any other camera for that
matter).

I've been watching the thread on durable cameras.  I'm certain there are
stories of drop survival to a hard surface, but I'm also certain this is a
very rare exception, not the rule.  The magnitude of forces exerted on
components within a rigid object dropped to a hard surface, even for a
short distance, is much, much higher than most people begin to imagine.
So, for the benefit of those who have dropped one of their Oly's, almost
dropped one, and those who imagine it will easily survive being dropped,
here are some details about what happens when you drop a rigid object to a
hard surface.

When I was in grad school, there was a researcher there who had made
himself famous destructively bashing motorcycle helmets using a huge room
of sophisticated bashing machinery.  A couple years later I hooked him up
with a close friend who happened to be an aerospace surgeon and was part of
a team evaluating helicopter pilot flight helmets.

What I learned from them as a result of introducing the two to each other:
There is a fine balance between a number of factors for survival of
contents inside the outer shell.  In the case of a "brain bucket" it's
one's head (a good one saved mine once).  In the case of cameras it's the
electronics and mechanicals under the body shell.  Too much flex allows
interior contents to get deformed or fractured by intrusion of the cover.
Too little flex transmits too much of the kinetic energy through g forces
and shock vibration to the interior which must somehow absorb all the
energy not absorbed by the outer shell.  When the object stops moving
(relative to whatever it strikes) the kinetic energy *must* go someplace
(Law of Energy Conservation).  If the outer shell cannot dissipate it, the
innards must (and will)!

Try hitting a wood handled hardened steel hammer on a concrete floor *very
lightly* [I don't want anyone hurt by a piece of chipped concrete!].  You
will feel the shock vibration up the handle into your hand.  Anyone who has
ever driven a metal stake into the ground using a sledge hammer *knows*
when it hits a large, hard, immovable rock!  The shock vibration up the
handle can leave your hands numb.

Dropping an object 1 meter (3.28 feet) to a hardened concrete floor occurs
in about 1/3 second with a terminal speed of about 11.27 kph (7 MPH).  This
is faster than the feds test the bumpers on our cars.  Still, it's not all
that fast, however terminal speed is not what does the damage.  The
magnitude of deceleration at the end does all the damage.  This can produce
upward of 500 g's of force with near instantaneous deceleration on at least
the part that first contacts hardened terra firma.  500 g's is decelerating
from 11.27 kph to zero in about 6 milliseconds (a little over 1/200
second).  How much of the falling object must decelerate that quickly
beyond the portion that first impacts with the ground depends on flex and
deformation of the outer shell (and flex/deformation of the surface it
hits) which allows the rest of the body to stop over a longer time.  Damage
can indeed be caused by external shell flex or deformation intruding on
internal parts.  It is also caused (and very often is) by inability to
survive the incredibly huge deceleration and the shock vibrations resulting
from it.  This is not to dispute how internal damage previous posters have
cited actually occurred, but to point out another very common failure mode.

Even if 400 of 500 g's is dissipated by the shell, the interior components
tied firmly to the shell and frame will still become 100 times their normal
weight very, very suddenly for a very, very short time.  Knowing this, it
should not be much wonder that with many modern materials, the outer shell
can reasonably survive with minor denting and scuffing at point of impact,
but internal components look like they've been hit with a hammer.  In
effect they have been; the hammer was their own inertial mass.  Any camera
that survives a 1 meter drop to a hard surface and still functions to
original specifications is indeed very well built!

-- John 

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