Ground testing altimeter, e-matches and ejection charges - need advice

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I have used 2 e-matches in parallel on both the SL100 and SLCF, but using a 1S 350mAh 25C LiPo. I did this to both the SLCF and SL100 roughly 8 times on each altimeter, between actual flights and bench testing. I still use those altimeters and I never experienced a failure due to the choices of LiPo or parallel. According to the logs in the altimeters the current draw was typically somewhere around 5 amps when using dual e-matches in parallel.

Having said that at this stage I use single e-matches but dual altimeters. I also switched from a 1S to a 2S just to give me a bit more margin on the voltage. Two other changes I made to my battery choice were to lower the mAh from 350 to 250 and the C rating from 25 to 20. This gives me a better margin of protection for max current draw which works out to roughly 5 Amps, give or take.

To calculate your max current divide your mAh by 1000 and multiply by the C rating. So a 250 mAh is 250/1000 = .25x20=5Amps

Thanks for sharing your experience. The new lipos are 180mah, 25C, so that puts me at 4.5 amps. question though: in all the specs I see two C numbers - in this case 25 /40. Does this factor in at all?
 
Thanks for sharing your experience. The new lipos are 180mah, 25C, so that puts me at 4.5 amps. question though: in all the specs I see two C numbers - in this case 25 /40. Does this factor in at all?
Sustain / burst. In theory you can pull up to 8A briefly, but the V will tail off pretty rapidly.
 
I am a big fan of eggtimers wifi switches- nearly perfect!

I really like the idea of that.

Update for those who care: I did my deployment tests yesterday and looks like .75g of BP for both drogue and main. Calculations were coming up at .5g each but I bumped it up a little just to be safe. Laundry pulled out nicely and shear pins properly sheared. Also got the smaller lipos on board now. So basically I'm all systems go for my L2 flight with this at LDRS in a couple of weeks. Thanks to all for the advice, and if you'll be at the event, I hope I'll have a chance to thank you in person.
 
Hijacking this thread, so please forgive.

I am ground testing right now for a hopeful launch this weekend.

This is my first time with electronics, so I do not have any experience with how altimeters such as the Marsa, and the Aim Xtra behave in ground testing.

I think everything is working correctly.

I have a flower vase that swallows the entire AV bay, with some foam gasket on the rim. A piece of plywood is the lid, and the rubber hose end fits well, When I start each unit, and put the vacuum to it, the units do not fire until the vacuum is OFF for maybe a second or 2. This is without removing the lid at all during the sequence.

A couple of seconds after that, the second string of charges fire. Both units give similar results for both events.

Does this sound correct?

The 'Apogee' event does not happen until the vacuum is turned off, using the switch.


I am still feeling very cautious about this, and do not want to have a hardware failure (operator error) that could have been detected at this stage. The launch is on Saturday. Too much effort involved to risk a launch not knowing.


Thanks, in advance!
 
Hi Chris,

Your test results are as you would expect. The apogee event occurs when the vacuum has passed its maximum value (highest "altitude"), and the main event occurs when the vacuum bleeds off to the equivalent 500'-700' level for a nominal main deployment. These tests are good for confirming that your altimeters are functioning. You also need to perform the deployment charge tests to determine the correct amount of BP required for each event. This will not require the altimeters.

If you're anxious about the launch, use a detailed check list and stick to it! There is no shame in double or triple checking your preparation for this launch.

Have a great launch.
 
Thank you.

Testing the charges seems so much more simple. So far, I am seeing consistent separation, and not excessive energy. The electronics, I have no way of quantifying when they fire, whether by light bulb, or by spark. Both are working, and seem consistent. Kinda. The other part... the sections end up separated with cord and things on the lawn every time. I have not tested a backup of 1.5 times the main charges. That comes tomorrow.

Also, I was thinking a bit higher for the main deployment, in order to give more time for tracking, and for the GPS to lock again, in case it loses it. Was thinking about 1200'? Too high? Or, since the total expected altitude is only about 2400', a lower altitude is okay? i will be using GPS, and also RF tracking. Newbie to both.

Fingers crossed!

Cheers!
 
I also use the Aim Xtra. I would be surprised if it couldn't re-lock while on drogue. 1200' does sound a little high, but it depends on how far you want to walk if the the wind up there is a bit stronger than expected!

If you are using GPS telemetry and RF tracking as well, make sure no one else is on your frequencies at the time. I assume your club uses appropriate frequency and operational separation.
 
Yes, I will definitely check on that. Thank you.

The wind will probably be present. i guess I should lower the main deployment altitude.
 
Yes, I will definitely check on that. Thank you.

The wind will probably be present. i guess I should lower the main deployment altitude.

Depends on when on Saturday you plan on making the Cert attempt, in the morning winds should be 5-7mph, starting at 11am until 5pm or so they start going up toward 10-15mph. Good news is a 500-700' deployment altitude should be okay for the wind and our flying field.
 
Thanks, Rich.

I think we will be arriving Friday evening. As a newbie, I will wait until my turn comes. If I arrive (which I think I will if everything is 'ready for launch') I will be ready to launch when we arrive, as soon as someone says that it is time, plus the time it takes for me to download the current 'space vehicle almanac' to the Aim unit, and get the local google maps info into the laptop, plus some time to get things prepped. So... next year? :) Kidding.. That bit will probably happen while the sun is coming up. Today's testing was the most critical (seeming) part. It sounds like the electronics are working correctly, though. I hear pops on the 2 main, and also the 2 backup channels.

It feels like there is no margin for error.
 
Thanks, Rich.

I think we will be arriving Friday evening. As a newbie, I will wait until my turn comes. If I arrive (which I think I will if everything is 'ready for launch') I will be ready to launch when we arrive, as soon as someone says that it is time, plus the time it takes for me to download the current 'space vehicle almanac' to the Aim unit, and get the local google maps info into the laptop, plus some time to get things prepped. So... next year? :) Kidding.. That bit will probably happen while the sun is coming up. Today's testing was the most critical (seeming) part. It sounds like the electronics are working correctly, though. I hear pops on the 2 main, and also the 2 backup channels.

It feels like there is no margin for error.

Dave our club President flys the Marsa altimeters so if you have questions about it he would be the best one to answer them. HPR flying will not open until Saturday morning as Friday is FAR101 rockets only. The biggest landmark for you to look for is the truck scales on 395 north of Pasco, they are a 3-4 miles past the little town of Eltopia. I will email you my cell so that if you have problems you can call me, we have excellent cell service at the site (a cell tower is about a mile or two away). I take it you are planning on camping on site? You can find me by my Maroon and Silver F250 parked usually near a old blue pop up canopy usually directly across the parking lot from the entrance to the range. We have several good landmarks that I can point out as you get closer to the site ( Scales, Crop Duster airport, Irrigation ditch, turn off the paved road.....:)).
 
Okay one last question: In my effort to keep things as reasonably simple as possible, I'd like to direct-wire my e-matches to the altimeter. I'll be using glove tips for the ejection charges. My current setup uses a pull-pin switch to arm, but I'm realizing that without terminal blocks on the bulkheads or some kind of connector, there's really no easy way to connect the charges unless the sled is outside the coupler. Meaning I will have to pull the pin and arm the altimeter for the minute or two it takes me to button everything up and re-insert the arming pin. That doesn't seem ideal or safe. It seems like my best (and only?) option is to eliminate the switch and just use twist and tape to arm. I'm fine with this (basically copying CrazyJim's Darkstar build stickied in this sub-forum) but wanted to see if anyone had other ideas I may be missing.

I'm getting ready to set up for dual deploy and was wanting to use a pull-pin switch.

I did not think of this potentially hazardous case during assembly.

Great thread!
 
I'm getting ready to set up for dual deploy and was wanting to use a pull-pin switch.

I did not think of this potentially hazardous case during assembly.

Great thread!

The light finally illuminated. I see what the concern was before. I’m slow sometimes.
I attach my switches directly to the switch band, rather than the sled with wires long enough to reach the sled as it’s removed.
A terminal strip on a bulkhead would be an even better way to handle this.
 
I don’t use two ematches per output. But I do use redundant altimeters on my larger rockets. It takes a lot less time to prep than to replace the rocket and all its parts.

I usually fly redundant setups on 4" and larger air frames, single altimeters for 3" and below. That may change as electronics get more compact. For single altimeter setups, I have used parallel e-matches with success. I may switch over to series and do some ground testing.
 
I attach my switches directly to the switch band, rather than the sled with wires long enough to reach the sled as it’s removed.
.

Aaha! That's the ticket. Steve what's your trick for attaching it to the switch band? I may look in to this setup myself - might be tricky on my 2 inch rocket. I'll probably just add a terminal strip ultimately since that's the easiest solution. Still plan to twist and tape for this first flight.
 
Aaha! That's the ticket. Steve what's your trick for attaching it to the switch band? I may look in to this setup myself - might be tricky on my 2 inch rocket. I'll probably just add a terminal strip ultimately since that's the easiest solution. Still plan to twist and tape for this first flight.

I use slide switches rather than pull switches and I just screw them to the switch band. But I’m very impressed with the microswitch holder Chris Attebery (I apologize for any misspelling of his name) makes for use as a pull switch and I want to figure out how to adapt that to attach to the switch band.
 
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I use slide switches rather than pull switches and I just screw them to the switch band. But I’m very impressed with the microswitch holder Chris Attebury (I apologize for any misspelling of his name) makes for use as a pull switch and I want to figure out how to adapt that to attach to the switch band.

I'd encourage a slight re-design for that printed holder where you have a curved piece in the front to match the inside diameter of the coupler/switchband. Hole for the pull switch would be centered in this and you'd attach with some small button head hex screws from the outside. Imagine what a crossbow looks like. Switch perpendicular to the curved attachment. Edit: now I really want to get myself a 3d printer!
 
I'd encourage a slight re-design for that printed holder where you have a curved piece in the front to match the inside diameter of the coupler/switchband. Hole for the pull switch would be centered in this and you'd attach with some small button head hex screws from the outside. Imagine what a crossbow looks like. Switch perpendicular to the curved attachment. Edit: now I really want to get myself a 3d printer!

Sounds good!
 
A follow up on this thread since I started it way back when...

After all that testing and hemming and hawing... unfortunately my L2 flight had a non-optimal outcome. Short version: drogue charge didn't fire at apogee but the main did at altitude. It could have been much much worse. Aside from shredding my brand new chute, zippering my payload section and breaking my fancy printed nose cone tracker sled, the rest of the rocket survived - including and most importantly all of my electronics.

I got voltage error beeps when I powered the Stratologger back up for both the drogue and main channels. My takeaway: even though the Lipo I used was ok'd by the manufacturer, next flight I'm sticking with a 9v battery. Only one ematch per charge (though the SL instructions suggest two) and a Adept22 installed as a backup.

I've learned so much from this - especially from the failures.

The good news: flew my LOC Vulcanite the next day on a J285 - motor eject - for a successful L2.
 
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