HPR avionics for an L2 cert (Eggtimer Quantum)

[arcanum___]

I am working on a rocket for my L2 certification and I'm planning to fly two Eggtimer Quantums, but I'm not sure how exactly to set up switches. Since they have separate terminals for power to the computer and power to the deployment channels, I want to use a common battery for the deployment channels of both Quantums and use a separate power battery to power each altimeter (for a total of three separate batteries). I also want to minimize the number of switches I'll need to use when the rocket is on the rail (to one screw switch).

So here's my current plan, I would like feedback on it so I can tell whether it's a good one and what I should change to improve it.

If I understand correctly, since the altimeters are armed via WiFi after being turned on, it should be safe to turn them on before taking the rocket to the pad and then arm them once the rocket is upright. However I don't want the battery for the charges to be connected until the rocket is upright, so I will use a screw switch, which will stay open until right before I arm the altimeters. This way, that is the only screw switch which I'll have to turn when the rocket is on the pad. I'll then be able to arm the altimeters once everything else is done.

 

[Kane]

Your approach makes sense for the reasons you list. However, utilizing a single switch to provide power to both Quantums negates the point of having redundant altimeters. If the screw switch fails (not uncommon), both your primary and backup deployments are gone. Same issue arises if you plan to use a common battery for deployment channels. It negates any benefit of redundant altimeters.

I use redundant Quantums on nearly all my rockets. I do not use a separate mechanical switch and each Quantum gets a single, dedicated battery. My altimeter bay is usually the last item I button up, but I connect power to the Quantums at my prep table. I generally use 7.4V 400 mAh 30C LiPos. I have only run out of juice when the rocket sat out at the pad for over 4 hours.

I would reconsider using any "common" power sources or common switches. Single dedicated batteries for each altimeter is simpler and more secure. If you feel you just add a mechanical switch, you should use one for each altimeter.

 

[Rocketclar]

What Kane above does is what I do. I always fly with two altimeters that each have a battery and separate switch. Each flight has 4 charges with 2 for each altimeter. I run the backups with 10-20% more BP and set the backup altimeters to 1 to 2 sec later for the drogue and 100' lower for the main. From flight profiles, I have seen that the backups do their job in a few cases, pushing the laundry out when the primary didn't, even though I had ground tested. BTW....I record all the testing data in an Excel sheet so that the next time I'm going to fly that rocket, I have what I had tested and used. Helps me with the prep.

 

[arcanum___]

Thank you both for the advise! I suppose I'll get rid of the screw switch and go to one battery per altimeter.

 

[cerving]

You're better off with a separate SINGLE battery for each Quantum. Having a single battery for the deployments on both Quantums is sacrificing redundancy, which is the point of having two altimeters.

Set up altimeter #1 to fire the drogue at nose-over, and the Main at 700 or 800 feet, set up altimeter #2 to fire its drogue one second later and subtract about 200' from the Main setting you chose for altimeter #1. Turn off the Failsafe on altimeter #1, and set the Failsafe on altimeter #2 (the backup) for 125 fps and 1250 ms... that way if for some reason your drogue never comes out you won't come in ballistic.

 

[Kane]

Good luck with your cert flight!
If I can offer any additional advice, it would be to use a checklist. Do a dry run of your prep procedures to get the checklist in line with how you set up. This is the best way to ensure you don't forget anything when you're out at the field.
I have shared some of my checklista on TRF and the NAR Facebook page before.

 

[arcanum___]

Thanks again! I'll make sure to follow all these recommendations.