Eggtimer Rocketry Eggtimer User Manual page 32

almost never happens, because you usually angle the rod/rail at a slight angle so that the rocket takes
off away from the flight line. This results in the velocity disparity that we've previously mentioned.
The rocket usually has some forward velocity at apogee; hopefully it's relatively small so your
parachute deployment happens at a low velocity and won't cause any mechanical problems like a
broken shock cord or a zippered tube. It also means that you really don't know that you've reached
apogee until after you've been there because you can't define apogee as when the altitude change
reaches zero, because velocity won't be the same as altitude change if you have a horizontal velocity
component.
Accordingly, the Eggtimer fires the drogue parachute at Nose-Over, which we define as one second
past apogee (highest recorded altitude). If the rocket is still going up, chances are that its altitude is
going to keep increasing before a one second interval elapses, so you're unlikely to get a false
apogee detection. If the rocket hasn't gained any more altitude after one second then you must be
starting on your way down, so the Eggtimer fires the drogue at that point, for a time determined by
the CHB ON setting (or 3 seconds for a servo). Assuming that the mechanical portion of the drogue
mechanism is working properly, your drogue chute will pop out and your rocket will start slowing
down.
If you run out of flight memory during an actual flight, drogue and/or main chute deployment WILL
occur. These events are not dependent on recording the flight samples, they are only dependent on
time/altitude and therefore are completely independent of the recording process. The recorded
deployment altitude and time ARE dependent on the recording process, however, so you may not get
an accurate deployment altitude/time in your flight summary download if this happens.
When Nose-Over is detected, the Eggtimer begins using the Descent Samples value for altitude
sampling. This setting is typically very low, 2 samples/sec is good and in most cases 1 sample/sec is
fine too. As the rocket descends, when the altitude drops below the Main deployment altitude the
Main channel is triggered, for a time determined by the CHB ON setting (or 3 seconds for a servo).
At this point your Main chute should pop out, to thundering applause and a hearty round of high-
fives all around.
On the Ground
The Eggtimer detects that your rocket is on the ground when the AGL altitude is below 30 feet for
over 5 seconds. Unless you launched from a hill, it's unlikely that your landing altitude will be
lower than that by a full 5 seconds times the descent rate, which is typically about 20 feet/sec for a
main chute. That works out to a landing altitude 100' below your launch altitude, which would be
unusual.
What is more likely is that it won't be able to figure out that you've landed, generally because your
rocket landed on high ground or a tree. If that happens, it will continue to record altitude samples at
the Descent Samples setting, until it runs out of flight memory. When that happens, it will call it a
flight.
Once on the ground, the Eggtimer will start beeping out the maximum altitude continuously for
anyone within earshot to hear. If you have the Telemetry option turned on, instead of beeping out
the peak altitude it will send out the apogee and elapsed time through the serial port continuously
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