Model Forum / General / Rockets / March 2008

Best way is to use Fred Wallace and place him face down in the dirt
and slime where he feels more at home (hell he used to sleep with the
slime ball that was left form  his dead momma ), with his pants around
his ankles. Duct tape hand and feet together and super glue a strike
anywhere match on thetip of his nose, and place nose firmly in contact
with striker material for match. Tape end of fuse  so it is in contact
with match tip on Freddies nose, and run rest of fuse to rocket motor.
When ready to launch, poke Freddie in his a.shole (in other words just
touch him anywhere since FREDDIE is a big a.shole anyway) with the end
of a broom stick. His natural reaction other than backing up on the
broom stick thinking its Darrell or Phil, will be to arch up and make
the nose and match strike the friction material........

Ohm's Law: The voltage drop across a resistor is equal to the current
times the resistance, or   V = I * R

The entire circuit (with the continuity button pushed but not the launch
button) has some resistance R. This is the sum of the individual
resistances in the circuit: igniter, light bulb, switch, and the wire
itself. To simplify things we can assume the switch and wire have zero
resistance; that's never the case but it's usually small enough to
ignore. So R = Ri + Rb  (Ri is igniter resistance, Rb is light bulb
resistance).

You are using a known battery voltage, 12v in this case. So the current
flowing through the circuit is:

             I = V/R = V/(Ri + Rb)

Most hobby igniters (e.g. Estes) require a relatively high current for
ignition, around 1-2 amps. Light bulbs have fairly high resistance, so
with the light bulb in the circuit the current is small, below the level
needed to fire the igniter. When you press the launch button the circuit
now has a low-resistance alternate path around the light bulb. The
current is now (approximately):

             I = V/R = V/Ri

Estes igniters have a resistance of about 0.8 Ohms, so with a 12v
battery the current is more than enough to fire the igniter.

Low-current igniters, like electric matches, need very little current to
fire--around 0.1 amp or less. The light bulb doesn't have enough
resistance to limit the current, so even without the launch button
pushed this circuit is not "electric match safe". But LEDs (with their
associated resistor) have enough resistance to drop the current to a
safe level. Just replace the light bulb with an LED and a resistor in
series.

Add the piezo buzzer in series with the LED & resistor.

Steve Humphrey