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Highlights of recent developments on the DoubleSShot project
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- Rick Maschek cast a sample grain using the reworked mandrel (polished
and slightly tapered). Unfortunately, the rework did not help as Rick
had similar difficulty removing the mandrel as before. A proposed
modification to the mandrel was subsequently discussed. This involves
cutting slits into each of the seven star points to increase flexibility
of the mandrel. A slightly tapered tube would be inserted into the
mandrel core prior to casting, in order to slightly expand the mandrel
(max at the top, zero at the bottom). Following casting and curing, the
tapered tube would be removed, causing the mandrel to contract. Combined
with the increased flexibility, the mandrel removal should require much
less effort. Two concerns arose. One was whether the 25 psi clamping
pressure on the propellant during cure would "collapse" the slits, and
the second was whether expanding the mandrel would cause the mandrel to
crack. Ben Brockert kindly agreed to put our SolidWorks software to good
use and perform a finite element analysis to determine if either
concern was warranted. The analyses indicated that neither problem would
likely occur. The deformation due to the clamping pressure was indicated
to be relatively small, and the stress levels were well below the yield
strength of the delrin. Special thanks goes out to Ben for such quick
service.
Drawing of the proposed modified mandrel and jig plate to serve as a
guide:
http://sugarshot.org/downloads/slit_mandrel.gif
Deformed shape plot and stress results with 25 psi clamping pressure
applied (note deformation greatly exaggerated):
http://sugarshot.org/downloads/mandrel_stress_case1.jpg
Deformed shape plot and stress results of expanded mandrel (note
deformation greatly exaggerated):
http://sugarshot.org/downloads/mandrel_stress_case2_1.jpg
Deformed shape plot and stress results of expanded mandrel:
http://sugarshot.org/downloads/mandrel_stress_case2_2.jpg
- In order to cut the mandrel slits, a "custom made" hacksaw was
fabricated by Richard. This hacksaw was fitted with an 18 inch (45 cm)
long blade (a normal hacksaw has a 12 inch (30 cm) blade). Also
fabricated were two "jig plates" which are to be clamped to each end of
the mandrel to guide the cutting of the slots. Rick will be doing the
mandrel modification when he receives the parts.
Photo of the jig plates, threaded rods and custom hacksaw:
http://sugarshot.org/downloads/dss_bps_047a.jpg
- Craig Peterson has conducted vacuum testing of the GoPro battery. The
results were positive, with performance under conditions of near vacuum
being very similar to performance at ambient pressure. No physical
changes to the battery were noted as a result of performing in the
vacuum chamber.
Craig's report:
http://sugarshot.org/downloads/3.7v_gopro_lithium_battery_test.pdf
Alberto has kindly uploaded the other test reports that Craig generated:
http://www.sugarshot.org/documentation_old.html
- Marco Torriani has proposed a new ceramic-based casting tube
insulation material. Following discussions of the method with Richard,
Marco has agreed to fabricate a prototype and conduct testing. Marco
also suggested a ceramic insulator for the nozzle which holds promise
(the current ablator was found to have suffered much greater ablation
than expected during the DSS BP motor firing).
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-Sugar Shot to Space is on facebook. Check us out.
http://tinyurl.com/2exr92k
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No amount is too large or too small. Every donation brings us closer to
our goal of reaching Space. Make a donation today.
http://www.sugarshot.org/sponsors.html#Donors
http://sugarshot.org/spons
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