Eggtimer Rocketry Eggtimer User Manual page 18

Field Descriptions:
A Launch Detect Altitude <50-500 by 50>
Also called LDA, this sets the altitude Above Ground Level (AGL) that the Eggtimer uses to
detect that a valid flight is in progress. It can be as low as 50' or as high as 500'. It does several
things:
1) Provides a start-of-flight reference point that other events are compared to.
2) Starts the flight recording sequence to "regular" memory. Prior to reaching LDA, altitude
readings are saved into a special "rotating" pool of memory that gets overwritten after 50
samples.
3) Starts analyzing the velocity profile to detect burnout.
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4) Starts the Burn Timer.
The "correct" value of this setting depends on several factors:
1) The thrust-to-weight ratio of your rocket. Higher ratios will generally call for higher settings;
slower moving rockets may require a lower setting.
2) The Burn Sample Rate. Higher sample rates may require a higher LDA setting.
3) The temperature, time of day, and the wind. Yes, these are actually factors. Altimeter chips
are sensitive to changes in barometric pressure, so any extraneous factors that would cause the
pressure to change will have an effect on the recorded pressure/altitude reading. If it's a windy
day, or if the sun is starting to come up or set then the temperature will change more quickly, and
the base altitude reading may be thrown off if the rocket sits on the pad for too long. To
compensate for that, the Eggtimer takes five baseline altitude readings, then averages in a new
reading every 15 seconds while it's sitting on the pad. If the rocket is sitting on the pad for an
extended period of time, the baseline temperature and pressure will be more accurate than if the
first samples were used.
We recommend that you use the default value of 200' until you get some flights under your belt,
or if you know that burnout will be at a lower altitude than this (if so, however, your rocket is
most likely underpowered!) Ideally, this setting should be significantly less than the burnout
altitude of your motor (one more reason to use a modeling program!) Note that some functions
(such as burnout detection) require the altitude to be above the LDA setting before they will be
triggered, so if you are in doubt you should set the LDA a little lower.
B Ascent Samp/sec.
This selects the number of samples per second that are written to the flight memory during the
Burn and Coast portions of the flight, which begins at Launch Detect and ends at nose-over.
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