Re: AP900 yellow light

Joe Zeglinski

Thanks Rolando,

When I was tasked with designing foam inserts for our instrument's
shipping case, I recall seeing an ad. The challenge was "how to foam a
briefcase containing a 2 dozen flat of eggs". One approach was to fill the
entire space with foam - good for making omelettes.
The correct solution was a simple "open grid" of foam strips - which to some
seems counter intuitive.

Correct foaming decelerates the item SLOWLY, buy safely, before it
collides with the insides. This requires detailed knowledge of forces
involved, mass, and bearing surface - on all 3 axes. The maximum deceleration
must be "less than" what the most sensitive "part" inside the instrument can
sustain. It's all well and good to stop the mount from hitting the case, but
the motor bearings, etc, inside the mount can suffer from whiplash, even if
the mount is protected by the design. That's why some boxers are killed in the
ring by a hit fro a well padded glove - the skull stops without a scratch, but
the brain inside, hits the skull wall.

Always worry more about the "weakest" link, inside a foamed case.

Wish AP made well designed, and airline guerrilla drop tested, foamed cases
for their mounts.


----- Original Message -----
From: <chris1011@...>
To: <ap-gto@...>
Sent: Wednesday, October 17, 2007 4:18 PM
Subject: Re: [ap-gto] Re: AP900 yellow light

In a message dated 10/17/2007 3:13:04 PM Central Daylight Time,
J.Zeglinski@... writes:


Another thing to look out for, is choosing a too soft foam for a too small
case, for the mount. A proper design, by a case design company, will take
the account not only the weight of the mount section, but also the cross
section of the surface area bearing into the foam. As well, they would
the proper foam modulus, that will "decelerate" the mount before it crushes
enough foam, to stop it before it collides with the hard inside of the

Too many people take such things for granted, and put in any kind of foam
so the mount won't get "scratched", never mind damaged. Others, put in far
much foam, which stops the mount hard in it's tracks - not much better than
simply filling the case with velour covered concrete! Making moulded foam
instrument cases requires engineering knowledge, or at least a pretty good
grade in high school physics.
Good thinking. The mount itself can take lots of abuse, but the motor box
cannot. It must not touch any part of the box. It should be left to sit in
air. Same is true of telescope focusers. The focus knobs should be left
suspended in the air and not be allowed to touch any part of the case or
Otherwise the pinion will for sure get bent.


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