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[web/altusmetrum] / FAQs / ontime.mdwn

# Why is the pyro "on time" of your products only 50 milliseconds?

Altus Metrum flight computers are designed for use with low-current 
e-matches.  The e-matches available for use in the rocketry hobby are
mostly designed for use in the fireworks industry, where it's an
advantage to retain continuity after firing to allow series strings
of matches to be fired on a high-voltage DC ignition system.

The problem this poses for us is that it means battery drain continues
for the entire on-interval, even after the pyro device fires.  Since
many of our products include radio transmitters necessary for helping
to find the rocket after flight, "using up" the battery during pyro
events limits the time available to locate and recover the rocket 
after flight.  So, our goal is to balance "enough time to be sure we
fire the pyro" against "so long we're just running the battery down".

In bench testing some years ago, we measured an average firing time 
of about 13 microseconds for commercial e-matches using a fully 
charged single-cell LiPo battery.  That led us to choose 50 
milliseconds on-time.  In practice, this has worked out brilliantly
for more than a decade.

# Can I change the pyro channel "on time" to something longer?

On all Altus Metrum products, the dedicated apogee and main channels
use a fixed 50 millisecond firing interval that can only be changed
by modifying the firmware.

On products with programmable channels like TeleMega, EasyMega,
and EasyTimer, the programmable channels can have the "on time" set
to whatever you want.