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Posted by RoyJ on October 1, 2008, 9:57 am
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I was thinking the load cell was one of the pizzo hockey puck unit.
Picture makes it much clearer. So the inertia issue is not with the
actual load cell but with the pin that drives the load cell. And the
thrust boss has it own stop.
I have some projects in mind that are totally unrelated in terms of end
application but the setup would work great. Thanks.
Lloyd E. Sponenburgh wrote:
>
>> Interesting! The electronics and cabling is straight forward but a
> few
>> questions for those of us who don't do this for a living:
>> -What's a gerb? Suspect it is somewhat equivalent to a shotgun
> barrel
>> but.........
>> -What's CATO? Suspect the first word is Catastrophic......
>> -Do you have any more detail on the load cell mounting, especially
> how
>> the over run protection screws mount and work (both the thrust boss
> and
>> the load cell itself)
>
> There are a couple more very fuzzy cell-phone pix at
>
> http://www.pyrobin.com/files/les%20teststand1%2008-04-08.jpg
> and
> http://www.pyrobin.com/files/les%20teststand%2008-04-08.jpg
>
> that show how the load cell mounts under the thrust boss.
>
> It's shimmed under the mount end to allow the free end to travel down
> under pressure from the load post.
>
> The three crash-stop screws limit the travel of the load cup. But
> since the load post is not rigidly attached to the end of the load
> cell, the cell may over-travel under its own inertia after a violent
> over-thrust. A single large, fine-thread screw in the base, right
> under the end of the load cell arm (centered along the axis of the
> load post), prevents that inertial overtravel.
>
> A "gerb" is the correct pyrotechnic name for a "fountain". "Gerb" is
> derived from the old French word for "Sheaf of wheat", which roughly
> describes the pattern of sparks a gerb makes.
>
> Gerbs are a main-line product of all close-proximity pyro
> manufacturers. Because fuel variations occur, we sought to
> characterize every fuel batch. Measuring thrust and duration with a
> fixed weight of fuel at a fixed fuel density and a fixed nozzle size
> does that nicely.
>
> CATO means various things depending upon what rocketry guy you ask.
> Among them are "CAT(astrophic) O(verpressure)" and "C(atastrophe) A(t)
> T(ake)O(ff)".
>
> Basically, it means the device goes BOOM, instead of acting like a
> rocket motor. When it does, it really slams the load cell; thus, the
> need for protection. Most load cells of this beam type can withstand
> only 25-50% overload without permanent deformation.
>
> LLoyd
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>
> There's a .pdf with photos and schematics at
>
> www.pyrobin.com/files/
>
> just click on "load cell test stand.pdf"
>
> (Yes... it _may_ get a paint job. <G>)
>
> LLoyd