I just built a load cell test stand for characterizing our gerbs.

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

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. Sponenburgh wrote:
I just built a load cell test stand for characterizing our gerbs.

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

On Oct 1, 9:15*am, RoyJ 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)

Lloyd E. Sponenburgh wrote:
I just built a load cell test stand for characterizing our gerbs.

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

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
m:

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%20t...2008-04-08.jpg
and
http://www.pyrobin.com/files/les%20t...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

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:
RoyJ fired this volley in
m:

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%20t...2008-04-08.jpg
and
http://www.pyrobin.com/files/les%20t...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

RoyJ fired this volley in news9mdnRoQiaZ-
:

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.

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 news9mdnRoQiaZ-
:
I have some projects in mind that are totally unrelated in terms of
end
application but the setup would work great. Thanks.


By the way, those beam load cells are going for cheap these days.
Aeroconsystems.com sells them in various ranges for $30.00.

http://www.aeroconsystems.com/loadcells/index.html

LLoyd

On Tue, 30 Sep 2008 11:57:32 -0500, the infamous "Lloyd E.
Sponenburgh" lloydspinsidemindspring.com scrawled the following:

I just built a load cell test stand for characterizing our gerbs.

Since when did you start associating with a bunch of hunchbacked
aliens from the thirteenth moon of Yavin? (Yes, I googled "gerbs"


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)

Polish and wax the load cup and paint or anodize the base a deep,
wonderful cobalt blue.

-
If the gods had meant us to vote, they'd have given us candidates.
--------------