and all of the electronics from 2YikStik. Everything else is new for this
build.
-Meanwhile, Robert became interested in measuring the temperature of a nose
+Robert is very interested in measuring the temperature of a nose
cone and a fin on a rocket at speeds above Mach. This led Bdale to design
a [TeleMetrum](http://altusmetrum.org/TeleMetrum) companion board called
[TeleScience](http://altusmetrum.org/TeleScience) capable of hosting up to
-12 NTC thermistors for temperature data collection.
-As was the case with 2YikStik](../2YikStik), the plan is to fly two
+12 NTC thermistors for temperature data collection. As was the case with
+[2YikStik](../2YikStik), the plan is to fly two
[TeleMetrum](http://altusmetrum.org/TeleMetrum)+[TeleScience](http://altusmetrum.org/TeleScience)
setups, one mounted in the nose cone and one mounted in the fin can. The
one in the fin can will be responsible for apogee deployment, and the one in
## Design Details
-* 98mm [Performance Rocketry](http://performancerocketry.com) G-10 convolute glass air frame
+* 98mm [Performance Rocketry](http://performancerocketry.com) G-10 convolute glass air frame
+* 98mm [Performance Rocketry](http://performancerocketry.com) G-12 filament-wound glass couplers
* 75mm [PML](http://www.publicmissiles.com) phenolic motor mount
* [Shock Wave Rocketry](http://shockwaverocketry.com/) fiberglass 98mm Von Karman 6:1 nose cone
* custom fins, using 3/16 inch birch plywood laminated with carbon fiber
The TeleScience board supports connection of up to 12 NTC thermistors along
with other capabilities.
-Installing the electronics in the fin can bay was .. interesting. More later.
+Installing the electronics in the fin can bay is a *huge* challenge due to the
+restricted space between the MMT and airframe.
+
+### Fintenna ###
+
+On 2YikStik, one of the big disappointments was a very poor signal from the
+UHF transmitter on the TeleMetrum board mounted in the fin can. This isn't
+surprising, since the antenna was just a wire whip running in parallel with
+and very close to the motor casing. For this build, I decided to try
+something completely different.
+
+The quick summary is that I'm loading the two fins that don't have thermistors
+in them as an antenna. And it works brilliantly!
+
+Before bagging the fins with the CF and glass lamination, I put 1 inch wide
+copper foil tape on two of the fin substrates, running from near the tip
+down to the root. Then the fins were bagged with 2 layers of 5.7 oz 2x2
+twill carbon fiber and a 6 oz glass sanding veil layer on both sides, all in
+one bagging operation to ensure all the layers formed a strong chemical epoxy
+bond.
+
+After unbagging, while the epoxy was still somewhat leathery, I carefully
+cut the CF back at the root edge of each fin exposing the copper foil. The
+fins were then allowed to cure and get sanded normally. When installing them
+in the airframe, I oriented them so that the thermistor fin is on the anti-rail
+side of the airframe, and the two copper-foil-equipped fins bracket the rail
+side, with the copper foil sides facing each other across the rail-side valley.
+
+After applying fin to fin glass across the motor mount, additional copper foil
+tape was used to join the two fins, soldering the new foil to the foil embedded
+in the fins. I then cut a "gap" in the center of the space between the two
+fins, and installed a 1.5-20pF piston trimmer capacitor with the screw aimed
+aft, and a piece of small diameter teflon coax with two ferrite beads on the
+forward side of the gap. The coax was run through a hole near the root of
+the fin separating this valley from the ebay and terminated with an SMC
+connector to mate with the TeleMetrum board.
+
+I'm pleasantly surprised at how well this seems to work. With a Pro75 6xl
+case installed, the variable cap allows the antenna to be tuned to about 1.3:1
+SWR, and the resulting transmitted signal seems strong...
## Build
[Shockwave Rocketry](http://shockwaverocketry.com), with thermistors embedded.
The fins are 3/16 inch birch ply, tapered on the leading and trailing edges,
-then covered with one layer of 5.7 oz 2x2 twill carbon fiber and a layer of
+then covered with two layers of 5.7 oz 2x2 twill carbon fiber and a layer of
6 oz glass as a sanding veil, all vacuum bagged with West Systems laminating
-epoxy using a kitchen food saver appliance.
+epoxy using a kitchen food saver appliance. The two CF layers are rotated
+45 degrees from each other.
We're moving from the Giant Leap Rocketry 98mm Magnaframe-based Dynawind to
G-10 glass tubing this time around. Dynawind is lighter and strong enough,
but we want to use glass couplers this time around for more strength, and
that leads to fit issues with the Magnaframe-based Dynawind tubing. So even
-though it's slightly heavier, we're going with an all-gladd build this time.
+though it's slightly heavier, we're going with an all-glass build this time.
We'll lose a little bit of max velocity, but hopefully it'll all hang together
this time!
All rings and bulkheads were cut using a CNC milling machine from 3/8 inch
birch plywood. The fin forward and leading edge rings are made from 3/4 inch
-thick assemblies made by laminating two such rings with wood glue, to provide
-sufficient depth for milled fin slots.
+thick birch plywood, mostly to provide sufficient depth for milled fin slots.
Will add a pointer to build photos here once they are available.
projects / web / gag.com / blobdiff