Eggtimer Rocketry Eggtimer User Manual page 39

Building Your Rocket to Use the Eggtimer
Mounting
In order to use your Eggtimer with a rocket, it will need to be properly mounted and secured.
The Eggtimer is designed to be used with just about any rocket with a 1.35" dia. (BT-55) or
larger payload bay, so any rocket that will take an egg will easily take the Eggtimer. However,
there is some preparation that will be need to be done to secure it properly. If you're familiar
with egg-lofting, you know that you can't just throw an egg in the payload bay and expect it to
come back unharmed. The Eggtimer is no exception, like an egg it needs to be properly
protected from the forces of flight.
The easiest way to do this is to build a "sled" for it, a piece of 1/8" plywood or basswood that
can simply slide into the payload bay. If properly done, a sled can be easily removable for post-
flight downloading. Better yet is to build a payload bay out of couplers that fits into the rocket
between the booster and the main parachute sections, there are some excellent references for
constructing payload sections in the Appendix.
The minimum size sled that will work with an Eggtimer is 4" long. We recommend, however,
that you make the sled as long as the payload bay will allow; if you have a 6" payload bay, for
example, your sled should be the entire 6" in length. You do not want the sled moving around in
the payload bay during flight!
Mount the Eggtimer with at least two, preferably four, 4-40 screws and ¼" nylon spacers, and
use nylon washers on the top of the board if you are using metal screws. You can use self-
tapping screws if the sled is wood, but we recommend that you put a dab of CA glue in the holes
to keep the screws from coming loose. You can also use a small strip of ¼" plywood to stand-
off the board. If you use machine screws, put a dab of Loctite® on the threads before you install
the nuts, or use Nylock-type nuts. You can also use nylon screws, they are a little lighter but
they're more expensive too. NEVER use Velcro to mount your Eggtimer, it will generate static
electricity when you remove it and you may damage your Eggtimer permanently.
Some Mounting Hints
Batteries can be mounted in several ways. Small zip ties work well, so does double-sticky foam
tape for LIGHT batteries (like 80 maH LiPo batteries, for example). If it's a rechargeable
battery and you don't expect to remove it, a dab of epoxy works too. Do NOT use double-sticky
Velcro, it WILL come loose in flight and is a magnet for static electricity.
No matter how you mount the batteries, make sure that they can't work loose during flight. In
the case of coin cells, we recommend a holder with a positive closure; the "slide-in" holders are
asking for trouble. If you DO have to use a slide-in holder, make sure that the open side faces
horizontally, and use a zip tie or a few wraps of tape to ensure that the battery can't slide out.
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