Newsgroups: comp.robotics
Path: brunix!uunet!elroy.jpl.nasa.gov!usc!sol.ctr.columbia.edu!destroyer!cs.ubc.ca!fs1.ee.ubc.ca!ee.ubc.ca!markm
From: markm@ee.ubc.ca (mark milligan)
Subject: Re: Measuring the acceleration of an arrow.
Message-ID: <1992Dec2.173954.12223@ee.ubc.ca>
Sender: news@ee.ubc.ca (Usenet News)
Organization: University of BC, Electrical Engineering
References: <1992Nov22.203815.9006@hemlock.cray.com> <LAINS.92Nov23091801@world.std.com> <BENEDICT.92Nov30163019@chaos.utexas.edu>
Date: Wed, 2 Dec 1992 17:39:54 GMT
Lines: 68

In article <BENEDICT.92Nov30163019@chaos.utexas.edu>, benedict@chaos.utexas.edu (Thomas Benedict) writes:
> I've got a related question concerning guns.  To date no one has
> published diddly squat about the acceleration of a bullet down the
> barrel of a gun, and very little regarding instantaneous breech
> pressures.  The closest anyone has done to this is to make a
> specialized gun breech that has a tiny hole in it.  At the bottom of
> this tiny hole is a small piece of precision crushable metal.  After
> the gun goes boom, the height of the metal is measured.  From this you
> can get a good idea of the maximum breech pressure of the gun.  This
> tells you NOTHING about the instantaneous breech pressure, much less
> the acceleration.
> 
> I've come up with a nifty way of measuring acceleration, but it's kind
> of expensive, and seeing all of the neat ideas about measuring the
> speed and acceleration of an arrow, maybe you can help out.
> 
> My current idea is to have a specially made bullet with a small
> reflector on the end.  The gun is anchored and aimed at a small hole
> in a metal plate about 100 feet away.  Through this hole is aimed a
> laser, which through interferometry should be able to measure the
> speed of the bullet at any moment in time.  The distance of 100 feet
> or so should insure that the bullet has enough drop so that it doesn't
> go through the hole and shoot the interferometer (a nastily expensive
> piece of equipment).  Problems:  It's expensive, I don't know if an
> interferometer can measure supersonic speeds like that, and it ain't
> easy to set up.  Any ideas?
> 
> I'm clueless on how to get the other measurement, namely instantaneous
> breech pressure.  Using the crush metal is good only for maximum
> pressure, so it's out.  Using a commercial pressure sensor doesn't
> work either, because most of them aren't made to withstand thousands
> of atmospheres on one side, and only one on the other.  I can't
> remember any of the data from the max-breech pressure experiments, but
> the numbers were big (bigger than a few thousand atmospheres, I
> think).


I have seen comercial presure sensors designed for just that purpose. They are
VERY EXPENSIVE but are designed for artilery and balistic data gathering.

The company is PCB Piezotronics The product is the 118A Balistic Presure
Transducer, rated at 100,000 PSI and guaranteed for 2200 test firings.

Page 34 of their catalog says "For continuous prolonged testing of guns and
ammunition"



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