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Highlights of recent developments on the MiniSShot Project
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- The propellant grain "structural" test (
http://www.sugarshot.org/downloads/ms_grain_structural_test.pdf
), which was slated to be performed this past weekend, has been
postponed until next weekend. Rick Maschek reported that the "Short
Stack" motor casing, which was intended to be used in this experiment,
was discovered to have suffered structural weakening in an earlier
static firing. Subsequently, Richard fabricated a replacement tube
section and has express-shipped it to Rick.
16.5" (42 cm) length of Ameron tubing for grain structural test:
http://www.sugarshot.org/downloads/ms_010a.jpg
- Richard has rough-cast 3 of the 12 ablative casting tubes needed for
MiniSShot 2. Once all 12 are cast, they will be machined to blueprint
dimensions.
http://sugarshot.org/downloads/ms_013.jpg
- John Montello reports that he is working on the fin mastermold; which
is made out of polycarbonate. Polycarbonate was chosen as the mold
material because "it is see-through and will allow us to match the work
on both sides. The finished mastermold will be polished to ensure smooth
casting". The mastermold is about 2% bigger than blueprint dimensions to
compensate for shrinkage of the final parts.
http://sugarshot.org/downloads/dscn2417a.jpg
- Ed Mallory has volunteered to work with Chris King to see if
improvements can be made to the telemetry system to provide greater
reliability of signal transmission. Ed plans to focus on the patch
antenna design and placement on the vehicle. Ed writes:
"I have a patch antenna that I built several months ago. I have acquired
some test equipment. I had access to some state-of-the-art test
equipment, but even so, it was not easy. I made it from 1/32" G-10/FR-4,
double sided circuit board. I designed it with the program from the
Portland State Aerospace clubs site, and used a CNC machine to cut it.
There is a electrical characteristic of insulator materials called the
dielectric constant. It is a measure of how easily an AC signal can move
through the insulating material, and is referenced to air as the
insulator. It turned out that the values given for G-10 are averages.
I used that value, and it caused the antenna to be resonant at the wrong
frequency. I had
to determine the value for the material I was using, and plug that into
the spreadsheet. That led to
resonant frequency below what I wanted, so I had to remove more material
to tune the antenna
to 439.25 MHz. When seen on a spectrum analyzer, the antenna is very
narrow band in the
frequencies it transmits, but it is tuned to the correct frequency, and
does well. I need to set
up an "antenna test range" to study it more, and this is what I will do.
I will keep a journal,
and write a report on patch antennas, maybe radio transmission from
rockets in general also.
There isn't much for the hobby rocketry folks to read in the way of
telemetry and radio transmissions
from rockets."
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Project
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