Altus Metrum Easy timer e-match question

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Donnager

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I am going to use a pair of these to control air starting up to 6 extra motors. When I am trying to get them all started ASAP (when boost detected), I am having some pause.

I have tested and am certain there are no issues firing two matches at the same time, but, If I set two channels with the same lighting criteria to light at the same time, I could actually be trying to light 4 at a time, which *seems* like more than I may want to ask from a small battery through the timer. Altus metrum default shows a 0.05 second firing duration to each e-match, so I was going to be slightly nicer to the battery by setting the second channel to be separated by 0.1 second or so. I'd like to be sure that when the electronics function, I haven't put them to use in a way that will cause a problem.

I can either put in a second battery, I can leave the delay in there to be sure I'm not reaching too far with the little timer, or both. Also, I am leaning toward ground starting two and eliminate the (potential) problem that way, or just fly a smaller number and have some redundant e-matches in empty cases for post flight inspection to see how they worked, or add another timer (yuck).

Is there a general practice here that most use? I may be concerned about a non-issue.
 
Sorry I didn't respond to your question, I didn't see the notification.
What battery does it use?
Anything I want, really. I have been planning to use 400mAh LiPo's to pop two e-matches at a time, and they work fine testing. But there is this warning:
WARNING: Unlike most LiPo batteries made for hobby use, these batteries are made specifically for use with Altus Metrum flight computers, and do not contain an over-current protection circuit board!

I can put a second 400mAh battery, an 850 mAh, a lithium 9V, or whatever. I don't know if 4 e-matches at a time is a great idea from a reliability standpoint. When deliberately attempting to pop 4 at the same time through two channels, would it be a good idea to separate the two events by 0.1 second (or some number that would be invisible to me, but may help out the electronics), which may get past any voltage drop for the whole works during the match firing? Didn't want to over extend the battery, the timer, or the wiring. I'm not going to do any kind of analysis on this, just saw the warning, and thought about it for a little while.

My mind says probably a non-issue, or at least not a significant one. I just wondered if anyone buffered the timing of cluster firing for this reason.
 
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Can never be sure without testing but a good high C rated 2S LiPo should fire 4 ematches with ease.

The Altus warning is a good one and any of the LiPo's sold to power airplane/drone motors will work since these do not have over current protection.
A way to determine this is the LiPo's C discharge rating. Typically this is 20 to 45C. this gives the maximum output current, take C rating times the capacity to get max current.
Example: 400mA-hr with 20C rating = 8 Amps max current. If Ematch max firing current is 1Amp then four should fire without too much Voltage drop.
 
I am going to use a pair of these to control air starting up to 6 extra motors. When I am trying to get them all started ASAP (when boost detected)
I assume that whatever you are ground-starting has enough thrust on its own for a safe flight? The failure modes otherwise are obvious.

Many airstarts like this intentionally stagger the motors in pairs, not starting the second pair until after the first has burned out, and it can look pretty cool. But I'm sure you have your reasons for airstarting 6 motors just after liftoff.
 
I assume that whatever you are ground-starting has enough thrust on its own for a safe flight? The failure modes otherwise are obvious.

Many airstarts like this intentionally stagger the motors in pairs, not starting the second pair until after the first has burned out, and it can look pretty cool. But I'm sure you have your reasons for airstarting 6 motors just after liftoff.
Definitely. Mostly I am looking at the behavior of the EasyTimers and how to properly set (all the helpful) permissives to get the motors on when I want. If the air-started clustering doesn't work, it will just be a nice 1000' flight. The center will fly fine on its own. The rocket is also dual deploy, motor eject will not be used.

There are permissives and tilt inhibit that should prevent unwanted starts, but that is why I'm testing it. I have a couple of two-stage rockets that are on deck, and this is my first use of the Easytimers for this task. I want to see how long these actually take between the time I'm calling for fire, and air started motors are up to pressure. I was planning to configure the two timers slightly differently so I will be sure I understand the way the outputs behave.

This rocket (5.5" LOC Magnum) has 6-29mm's around a central 54, and there are two Easytimers mounted in it. My goal was to do as you describe, and stagger the 29's in pairs. My first preference is one ematch per output on each timer, which leaves me two unlit, so at least two outputs will be driving 4 motors if I air start all of them.

I'll probably just do a 5 motor test (4 lit by timer) in a couple of steps.
 
Firing pairs, opposite each other, is a good way to go. You can then delay a second or two between pair firing. This would look pretty cool.

Are you running an Accelerometer to determine time from firing igniter until motor produces thrust?
I run a 10DOF sensor logger on my 2-stage an use Eggtimer Quantum or Proton to fire igniters. Pretty easy to measure timing with data from both. I did have one flight where the AT D15T took 4 seconds to come up to pressure. That was not a good flight.
 
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