By Lance Alligood
The field I launch at is a large parcel of undeveloped land. While there are no trees, there are tall shrubs and
grass often making it difficult to see exactly where a rocket recovers frequently. I grew increasing tired of searching
(sometimes aimlessly) for my rockets. To help shorten my quests to recover, I modified a Radio Shack mini personal
alarm to attach to my rockets. The battery is a tiny, light A23 (12V cell that is about 2/3 the size of a AAA battery)
that is found in most garage door openers.
Only 2 items and 4 common tools are needed to build one:
- 1 Radio Shack "Mini Egg" Personal Alarm with Keychain (49-428), cost
- 1 wire clothes hanger
- Power drill with 1/16" drill bit
- Wire cutters
- Needlenose pliers
- Small Phillips head screwdriver
- OPTIONAL: Sandpaper
Start by removing the 2 small screws in the blue egg alarm. Remove the battery.
Pull the pin and remove the small links between the main keychain loop and pin. Attach the pin directly to the keychain
loop. (Now would be a good time to sand the pin to allow for less effort to remove the pin.)
On one half of the blue shell there is a small round post where another screw
could possibly go. Drill through the shell at that point. Reassemble the egg and drill through the hole just created to
put a hole through the other side of the shell.
Cut a 4" straight piece of wire clothes hanger. Slide it through the
plastic shell. Hold the wire with the needlenose pliers and bend the metal into a trapezoid shape so that there is
about 1/2" on each side of the egg and the ends fold against each other. This will allow you to still be able to
open the egg (to replace the battery!) and clip the wire onto/off of a screw eye.
Clip the wire onto the screw eye and the keychain loop onto the parachute attachment point. At ejection, the force
of the chute opening with the mass of the nose cone/payload will pull the pin and sound the alarm.
I have used this twice so far. First flight was with my PML Phobos with a G64.
The beeper was attached to the quickinks at the payload bulkhead and parachute. Even at ~1200ft, I could hear the
beeper immediately upon ejection. No damage. Second flight was with my USR Banshee on a F50-9T. The beeper was attached
directly to the bulkhead screw eye. This rocket is so light that I pulled the pin with the rocket on the pad. Altitude
was well over 2000ft but beeper was not audible until about 1500ft. Again, no damage upon recovery.
This is a very powerful beeper that was modified in less than 30 minutes to be used with many rockets in my fleet.
It can easily be moved between any rocket that has a body tube ID greater than 1.75". Weighing only 1.1oz, it also
comes with minimal impact on the rocket CG.
10/05 - "Yes this worked great, I used fishing snap swivels on each end so I could easily and quickly attach
it to any pre-build rocket. P.S. this alarm is ear splitting, and it warbles so as not to have the directional problem
that a straight single tone beepers would have." (L.L.)
09/05 - "I have used the same RatShack beepers on several high power flights. Simply tape the beeper to the
shock cord near a recovery mount with a couple wraps of electrical tape, then attach the pull-pin ring to a the quick
link. Make sure there is enough slack so the pin pulls from the beeper when the shock cord is extended to full
My EMRR - ERROR!
09/05 - "Lance gets a healthy three and one-half thumbs up for this beauty of an idea. After loosing my 3FNC
prototype in the Great Tree Line/Hay Field Incident of 05' I have been looking for an inexpensive, reliable,
prefabricated, non-radio frequency rocket locator and here it is. UPS just delivered two of the little beepers and I
can't wait to try them out. Thanks Lance! " (L.P.)
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