Eggtimer Rocketry Eggtimer User Manual page 52

prep because you don't have restring a wire across the terminals, and you don't have to install a
tripwire on the pad. The disadvantage is that you need to be very careful to make sure that the
switch closes completely while on the rail/rod, and that it can't accidentally be released until the
rocket leaves the pad.
High-Power Airstart Programming Example
This example is for a rocket using Channel B in Airstart mode, with both channels of the
Eggtimer being used to fire charges. In this case, the second stage motor's built-in ejection
charge will be used to fire the drogue, so you will need to model the flight carefully in order to
select the correct delay. The first stage's built-in ejection charge should be used to fire a chute to
bring that stage down, it should be timed to pop right around the first stage's projected apogee.
You may have to model the first stage's flight separately from the second stage to determine this
value, but it will usually be a few seconds after second stage ignition because the added drag will
slow the first stage rather quickly.
This example is for a rocket with a Thrust/Weight ratio of over 10/1, so the default 200' LDA
setting will work fine; in fact, we don't really want to increase it, because we don't want to run
out of pre-LDA memory (it holds 50 samples, so at 20 samples/second that's 2.5 seconds).
We are assuming that the main motor will fire for approximately 2.6 seconds, and that we want a
1 second delay after burnout before firing the second stage. If we know that our igniter will take
about .5 to ignite the second stage motor, the actual delay from burnout will be .5 secs, or 500
ms. Therefore, we will set the Airstart Delay to 500 ms which will fire the igniter as soon as the
Burn Timer ends, with the second stage motor igniting about one second afterwards. We also
increased the CHB On-Time to 3 seconds (from 2), since the igniter may take longer to heat up
than a simple electric match used to fire ejection charges. We recommend that you test the
igniter-motor combination on a single-stage flight first or consult other club members, forums,
etc., so you have an idea of how long it takes that particular igniter to fire that particular motor.
We're setting the minimum velocity to 400 ft/sec, we're assuming that our modeling program
showed that the rocket was going at least 500 ft/sec at second-stage ignition.
Eggtimer Build_1.48b
A 200 LDA <50-500 by 50>
B 20 Ascent Samp/sec: <4,5,8,10,15,20,25,33>
50 Interval (ms)
C 1 Descent Samples/sec <1,2,4,5,10>
1000 Interval (ms)
D 1 Main Mode <0-Off, 1-IGN, 2-Servo CCW, 3-Servo CW>
E 500 Main Altitude <100-2000 by 50, 0 @ Apogee>
F 2 Main ON-Time <1-9, 0-Cont.>
G 4 CHB Mode <0-Off, 1-IGN, 2-Servo CCW, 3-Servo CW,
H 3 CHB ON-Time <1-9,0-Cont.>
I 2600 Burn Timer <100-20000 ms by 100>
J 500 Airstart/Delay <0-9900 ms by 100>
K 400 Airstart Min Velocity <0-700 by 50>
L 0 Telemetry
O Comments:
Options: Esc, A-O, ?
Flight Settings
4-Airstart, 5-Airstart w/o Breakwire,6-Delay>
Airstart example
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T:23.50
P:97804.00
A:975.39
Main:0
CHB:0
Batt:3.12