User`s manual

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Mach Transition…
As your motor continues to burn and the velocity increases, if the velocity exceeds 800 ft/sec
aerodynamic shock wave pressure buildup can fool the pressure sensor into thinking that the rocket
is descending when in fact it is actually ascending at a rather rapid speed. If this were not taken into
account, the flight computer might deploy parachutes at near-mach speed, which would undoubtedly
break something and ruin your day, not to mention what an object falling from the sky at these
speeds could do.
To prevent this from happening, the Eggtimer TRS uses a predictive mechanism to hold off
deployments until it’s safely out of the mach “danger zone”. All deployments are inhibited on
startup. Real-time altitude readings are run through a filter, which “smoothes” the noise from the
pressure readings. The smoothed readings produce a much gentler velocity profile, which allows it
to be used to obtain reasonably accurate velocity samples. After the LDA has been reached, when
the velocity drops below 100 ft/sec for at least 1 second (presumably near apogee), deployments are
enabled.
Apogee and Nose-Over
Assuming that your rocket is moving more or less straight up, it will continue to slow down during
the coast phase until it gets as high as it’s going to go. If the rocket was going absolutely straight up,
the velocity at this point would be zero; it would simply start falling to the ground. In reality, this
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, since if you have a significant forward component it may still
go up a little bit.
Accordingly, the Eggtimer TRS 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 TRS fires the drogue at that point, for 2 seconds.
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 should run out of flight memory during an actual flight, drogue and/or main chute
deployments 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.