I just built a load cell test stand for characterizing our gerbs.
There's a .pdf with photos and schematics at
just click on "load cell test stand.pdf"
(Yes... it _may_ get a paint job. )
LLoyd
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)
Lloyd E. Sp> I just built a load cell test stand for characterizing our gerbs. >
I'm guessing a gerb is a section of a rocket motor, or maybe just a tube filled with rocket fuel used to test 'the mix', eliminating differences you'd see between different nozzles.
CATastrophic Overpressure?
Dave
RoyJ fired this volley in news:YeadnY8LV5mN5X7VnZ2dnUVZ snipped-for-privacy@earthlink.com:
There are a couple more very fuzzy cell-phone pix at
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
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 > RoyJ fired this volley in
RoyJ fired this volley in news:p9mdnRoQiaZ- HH7VnZ2dnUVZ snipped-for-privacy@earthlink.com:
Not quite. The load post is rigidly affixed to the load cup; it will either stop (or break loose) when the cup is stopped. The rounded end of the load post simply rests on the end of the load cell beam.
It's the load cell beam itself which, once accelerated to a high speed might over-travel its load limit. It flexes like a tuning fork tine.
LLoyd
RoyJ fired this volley in news:p9mdnRoQiaZ- HH7VnZ2dnUVZ snipped-for-privacy@earthlink.com:
By the way, those beam load cells are going for cheap these days. Aeroconsystems.com sells them in various ranges for $30.00.
On Tue, 30 Sep 2008 11:57:32 -0500, the infamous "Lloyd E. Sponenburgh" scrawled the following:
Since when did you start associating with a bunch of hunchbacked aliens from the thirteenth moon of Yavin? (Yes, I googled "gerbs" ;)
Polish and wax the load cup and paint or anodize the base a deep, wonderful cobalt blue.
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