User`s manual

- 28 -
The beep codes are:
Number of
Beeps
Problem
1 Battery Low Error (< 6.5v)
2 Altimeter Sensor or Hardware Error
3 GPS Error (no feed)
4 Channel A (Main) error - igniter/servo/battery
5 Channel B (Drogue/Airstart) error – igniter/servo/battery
Important: The self-test routine is executed ONCE when the Eggtimer TRS is powered on. In the
event that it passes self-test and a condition arises after it has passed, it will NOT notify you of this
fact. In particular, if you turn off the deployment power after the Eggtimer TRS has gone into the
Ready for Flight mode, the Eggtimer TRS will continue to report that it is Ready. However, the
deployment channel status WILL be displayed on the Eggfinder LCD display, so if this should
happen then you’ll be able to tell, hopefully before the LCO presses the button.
OK, we’re ready, so press the button already! ☺
In the Air…
Once your rocket is launched, altitude samples are taken at 20 samples per second. These samples
are saved into a special rotating pool of memory until the LDA altitude is reached at 200’, then they
begin to be saved into the “regular” memory. When your rocket reaches LDA, the velocity profile
data also begins to be computed.
Velocity readings are computed based on the difference in altitude between successive samples and
the elapsed time between the samples. In a perfect world, this would give you a precise and 100%
accurate velocity reading. The reality is somewhat different, however. There are several things that
can introduce errors into the velocity reading: angle of attack, wind, errors in the pressure readings
due to aerodynamic influences, and time differences. If you measure the launch angle prior to
launch, you can calculate this error, although anything (such as wind) what makes the rocket deviate
from a straight-vertical path will pretty much negate this compensation unless you had set the angle
to a really high value (over 15°). If the pressure ports in your payload bay aren’t sized properly,
this can introduce an error, particularly if they’re too big and you have two of them opposite each
other (you’ll get a crossflow through the payload bay which makes the pressure readings very noisy).
Finally, differences in the processor’s timing may introduce errors, although the readings are taking
at relatively precise intervals so it’s going to be very small.
The good news is that the magnitude of these errors tend to be proportionate to velocity as the rocket
ascends, so they respond well to being filtered with mathematical noise filters. We use a variation of
an exponential moving average filter to smooth out this “noise”, so transition to supersonic speeds
and back can be detected with relatively good accuracy.