OUTDOORS
MATERIALS
Cylindrical plastic pill bottle about 2½" long
to fit in a rocket payload compartment
Rubber balloon large enough to cut a 2" round
piece from
Button thread or heavy-duty sewing thread
6"-diameter wood dowel, 16" or longer
Model aircraft plywood,
6" thick, 2" square
Balsa wood,
1" thick, 2" square
Balsa wood, ¼" thick, 2" square
Scrap wood board, at least 4" square for G-meter
calibration stand
Small cylindrical spring, ¼" diameter
Washers:
6" ID ( 1),
4" OD ( 2) You’ll need more
of each for calibration, which you can do in the
hardware store aisle.
Heat-shrink tubing, ¼" diameter
Wood screw, about 1½" long
Wood glue or epoxy
CA (cyanoacrylate) adhesive gel
High-tack, double-sided foam tape
Paper Graph paper is best.
TOOLS
Model rocket with transparent plastic payload
section at least 5" long I used the Estes HiJax
(EST 2105), which has a 6" clear payload
compartment. Or you could make your own
from a spare body tube and nose cone mated
to a matching “booster.”
Drill and drill bits:
5",
6"
Saw for cutting wood dowel
Tool for cutting 1" rounds out of thin plywood
You can use a hole saw, but I rough-cut with
a saw and used a Dremel tool with the 401
mandrel bit to turn the pieces against a
sandpaper surface.
Altimeter or barometer a dedicated device, or you
can use a hiker’s wristwatch or a weather station,
such as one from RadioShack
Vacuum chamber or a vacuum food sealer
and vacuum bag
2" PVC pipe, 12" long
Colored pencils or fine markers
the bottle. This base will later accept a wood screw
to hold the chamber fast to the tube coupler at the
bottom of the payload section (Figures B and G).
Build the G-Meter
Cut a disk of
6" aircraft plywood just slightly shy
of the inner diameter of the rocket’s payload tube,
and drill a
6" hole in the center.
I did this in a fun way: first I traced the circumference of the body tube onto the plywood, rough-cut
142 Make: Volume
16
the disk, and drilled a
5" hole in the approximate
center by eye. Then I threaded the disk onto a
Dremel 401 mandrel bit (a shank with a screw-like
head at the end) and used the Dremel as a sort
of mini reverse-lathe, turning the disk down to
diameter against a piece of sandpaper tacked to
a board (Figure C). The mandrel bit is designed to
hold polishing bits, but hey, here’s a new use! After
sanding down the disk, I redrilled its center hole
out to
6".
Glue a 3½" length of
6" dowel into the disk, and
mark a scale on the dowel from the base to the end,
in
5" increments, alternating between contrasting
colors to make it easier to read (Figure D).
Slip a ¼" length of heat-shrink tubing over the
dowel, and shrink it down until it stays in place even
if you shake it like a thermometer. This is the G-force
band. Slide the spring over the dowel, followed by the
smaller washer and then the 2 larger washers. Now
shrink another ¼" length of heat-shrink — this is the
altitude band.
Prepare the Adjacent
Rocket Sections
Cut 2 more disks out of
1" balsa, to fit the rocket’s
inside diameter (Figure E). Drill one with a
1" hole in
the center and use CA gel adhesive to attach it flat
into the tube coupler piece that will take the bottom
of the rocket’s payload tube, about ½" down from the
top edge. This disk will anchor the altimeter chamber.
Drill a
6" hole in the center of the other disk and
use CA adhesive to glue it into the nose cone, flush
with its bottom edge.
The G-meter dowel will run through this disk and
slide farther in when higher altitudes cause the
pressure chamber membrane to balloon upward.
The altitude heat-shrink band will meanwhile stay
in place against the disk.
Photography by David Simpson and Linda Kennyhertz
Assembly: No Bouncing Around!
Use a short wood screw to secure the payload tube
coupler to the altimeter base (Figure F). Attach
the G-meter base to the altimeter membrane with
a
1"–
6" square of high-tack, double-sided foam
tape. Use a thin film of epoxy to attach the G-meter
base to the spring, the spring to the washers, and
the washers to each other (Figure G).
Drill a
5" hole through the side of the payload
section to allow external air pressure to reach the
altimeter.
