# First time use of electronics for redundant single deploy on L1 cert?

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#### rocketsam2016

##### Well-Known Member
A lot of folks advise not using electronics for the first time on a cert flight. I've been doing a lot of reading though and I'm *seriously* persuaded by the safety arguments in favor of having redundancy for HPR deployment events. As such, I'm leaning towards using my eggtimer quantum for the first time on my cert flight for apogee deployment with the motor providing a redundant second charge (delay set to be after the altimeter should fire). Either way it will be single deployment of the main at apogee, it's just a question of whether I wire up the altimeter to a charge or not.

This should be safer for me and everyone else and gentler on the rocket, at the cost of increasing the likelihood of human error since I'm complicating the prep process with something I've never done before.

Any strong arguments against doing this? The rocket needs a big H to fly safely enough for my tastes, so I can't try out electronics on it with a G motor.

#### rharshberger

##### Well-Known Member
A lot of folks advise not using electronics for the first time on a cert flight. I've been doing a lot of reading though and I'm *seriously* persuaded by the safety arguments in favor of having redundancy for HPR deployment events. As such, I'm leaning towards using my eggtimer quantum for the first time on my cert flight for apogee deployment with the motor providing a redundant second charge (delay set to be after the altimeter should fire). Either way it will be single deployment of the main at apogee, it's just a question of whether I wire up the altimeter to a charge or not.

This should be safer for me and everyone else and gentler on the rocket, at the cost of increasing the likelihood of human error since I'm complicating the prep process with something I've never done before.

Any strong arguments against doing this? The rocket needs a big H to fly safely enough for my tastes, so I can't try out electronics on it with a G motor.
No real arguments against this method as you have redundant and separate deployment initiation systems, one of those IS a recommended/suggested method of deployment for L1 (motor eject for simplicity).

#### Bat-mite

##### Rocketeer in MD
Yeah, it stinks that high-thrust G motors are considered HPR.

If I were you, I would use the Quantum with motor back-up. Drill the delay about two seconds longer than the recommended for apogee. If the Quantum fails for any reason, you still get the chute out, just a tad late.

Also, use two e-matches in series. Usually with e-matches, if one fails to ignite the pyrogen, it still passes current to the second one. It is not uncommon to have an e-match test for the right resistance, but fail to ignite the BP.

Do not wire them in parallel as this causes a current drain on the altimeter that may be harmful.

#### NateLowrie

##### Well-Known Member
I say go for it if you are comfortable with the electronics. You do have 3 options:

• Run 2 altimeters with no motor ejection charge.
• Run a single altimeter and use the motor ejection charge at the max setting for backup.
• Run 2 altimeters and use the motor ejection charge at the max setting for a 2nd backup.

A couple of Suggestions:
• Have the procedures for arming each altimeter with you and follow them. Add a step in your checklist to verbally confirm the final armed and ready for launch detect beeping sequence on each altimeter. I know the quantum is pretty simple but it's worth having. I trashed 2 TRS units and an airframe when I forgot the final arming step trying to do it from memory.
• The quantum's idle current rate is 70ma per hour. Make sure you use a lipo with enough current rating or you use a physical switch in between. I like to use a physical switch in between and turn it on while the rocket is still horizontal before going through the wifi arming sequence. That way you can button the av-bay up before the launch and not worry about the battery dying.
• Make sure your vent holes are sized right. If you post the numbers here we can run a double check for you. It's a good idea to use 3 or 4.
• GROUND TEST!!!! Make sure your charges blow the airframe apart and the laundry is ejected. What will you use for charge holders?
• Also, a good idea to ground test the avionics bay under vacuum conditions. Assemble the av bay and use LED's with resistors on the charge outputs. Plug all the holes except one and put the hose end of a vacuum on it. When the vacuum hits maximum suction the LED's should light indicating apogee charges fired. If you had main charges hooked up they would fire when you removed the vacuum.

#### ksaves2

The way to look at this is the electronics can act as ballast to limit the max altitude so would be an advantage at a site with a limited waiver. Would keep the rocket in sight. One might argue that the might as well do it purely electronic
to cut down on the risk of a zipper so scratch the motor ejection. Especially if the rocket is cardboard. If the motor blows early and zipper occurs, do not finish. That can be planned for with careful simulation though.
The problem with electronic is the neophyte would have to get BP and matches. Shouldn't be a problem if working with a large group. People are willing to share but would take some asking around and planning in advance.

I'd say if one feels up to the complexity on an L1 flight to do it. Have at it. If they want to keep it simple, simulate away with motor apogee ejection only and only use an impulse for the distance you care to walk on recovery.
This is not the time for a sight unseen flight or showboating. Git 'r done and start doing DD stuff with H's and I's once the cert is in hand. Can learn a heck of alot with that strategy. Kurt

#### TKnox

##### Member
I used an altimeter with motor ejection for single deploy on my level 1 cert flight. Key is to be comfortable with the function/use of your electronics prior to the flight. If you are, you should be fine. Instructions on-hand and a preflight/pad checklist will help ensure successful prep and flight. Go for it and good luck.

Trey Knox

#### rocketsam2016

##### Well-Known Member
Wow lot's of feedback! Responses:

- I'm using the dual battery option for the quantum (separate battery for the altimeter and for the firing circuit), and each battery is a 460maH 25C/40Cburst lipo. I've already killed one battery though by leaving it plugged in for a few days. The quantum doesn't have a low-voltage shutoff.
- Yes I have altimeter steps on my checklist (and yes I'm using a checklist, anyone have links to ones they use?)
- I've heard mixed thoughts on whether doubling up on ejection igniters increases or decreases reliability. I'm using the pratt ejection canisters for what it's worth. I'm inclined to use a single since I'm already letting the motor by my redundant charge.
- It's a fiberglass bird built like a tank so zippers are pretty unlikely. The "tank" part and my donut av bay is why I need a big H or more...
- I'm thinking a lot about vent holes. See this thread (https://www.rocketryforum.com/showthread.php?136536-Vent-holes-for-donut-avbay&p=1625517). Let's keep discussion of the vent hole sizing there though . I've got a (limited, from college) EE background and spent this morning reading old rocketry forum posts and pondering the math behind chained vent holes with different time constants.
- I've tested the altimeter using the quantum test mode and resistors + multimeters on the outputs. I haven't cut the vent holes yet so I haven't done a vacuum-based test though I will. I live in the city and have no LEUP so I can't buy BP or test charges until I'm at the field on launch day, though I've asked ahead and I can do ground tests there if I coordinate it with the RSO/LCO.

#### NateLowrie

##### Well-Known Member
Wow lot's of feedback! Responses:

- I'm using the dual battery option for the quantum (separate battery for the altimeter and for the firing circuit), and each battery is a 460maH 25C/40Cburst lipo. I've already killed one battery though by leaving it plugged in for a few days. The quantum doesn't have a low-voltage shutoff.
- Yes I have altimeter steps on my checklist (and yes I'm using a checklist, anyone have links to ones they use?)
- I've heard mixed thoughts on whether doubling up on ejection igniters increases or decreases reliability. I'm using the pratt ejection canisters for what it's worth. I'm inclined to use a single since I'm already letting the motor by my redundant charge.
- It's a fiberglass bird built like a tank so zippers are pretty unlikely. The "tank" part and my donut av bay is why I need a big H or more...
- I'm thinking a lot about vent holes. See this thread (https://www.rocketryforum.com/showthread.php?136536-Vent-holes-for-donut-avbay&p=1625517). Let's keep discussion of the vent hole sizing there though . I've got a (limited, from college) EE background and spent this morning reading old rocketry forum posts and pondering the math behind chained vent holes with different time constants.
- I've tested the altimeter using the quantum test mode and resistors + multimeters on the outputs. I haven't cut the vent holes yet so I haven't done a vacuum-based test though I will. I live in the city and have no LEUP so I can't buy BP or test charges until I'm at the field on launch day, though I've asked ahead and I can do ground tests there if I coordinate it with the RSO/LCO.

1. Do yourself a favor and use one of the 460mah batteries for both connections. It'll function just fine and it's easier to hook use. You can get a Y- harness with JST ends pretty easily if you want flexibility down the road.
2. I'll post my checklists for my level 2 here when I get home.
3. Single ematch per channel is fine. i along with most only use a single ematch.
4. Shove an I236 in it (assuming it stays in waiver)... You won't regret it.
5. You will get many different opinions on your last statement...

#### rocketsam2016

##### Well-Known Member
Nate:
1) Already have my bay set up to hold 2 batteries in place in a way that makes using a single battery doable but annoying, and soldered separate JST connectors to board to use 2 batteries. It adds a level of safety, and further since the drain on the altimeter battery is larger than the drain on the firing battery, it facilitates a running circle of batteries through the day (with voltage checks to confirm of course). Say I have 3 charged batteries. First flight is B1 (altimer) and B2 (firing). Second flight is B2 (altimeter) and B3 (firing). Third flight is B3 (altimeter) and B1 (firing). If any battery has an unusually large drain I can just drop it from the rotation too. I also just really like the idea of dual batteries for when I switch to dual deploy and having the apogee deployment short in a way that can reset the altimeter can be a little scary.
2) Thanks! That'd be awesome. Do folks have a bring-with-them-to-site checklist too?
3) Cool, agreed.
4) That was my plan originally, though mild pushback from site. Big H would go to 800 feet or so, I236 to 1325. Big H has advantage of even better thrust-to-weight ratio though (rocket has reached 7.5lbs dry, oooof!) I gather they've had some scary ill-prepped L1 certs show up in the past and it's my first time with the club. I've put a ton of time into thinking everything through, but they can't know that as confidently as I can.
5) Bring it on as long as folks don't mind, I'm here to learn and be safe and maybe the next newbie to HPR will learn from my questions too

#### ksaves2

With that expected altitude you should have no recovery "distance" trouble. Good Luck!! Kurt

#### kidrobo

##### Active Member
Probably just reiterating what most are saying, but if you are comfortable with the electronics then go for it. I used a dual altimeter dual deploy setup in my 2.6" Darkstar for my L1 because the electronics aspect piqued my interest. It also led right into my L2 flight.

I figure that if it is worth doing it is probably worth over doing.

#### Rex R

##### LV2
24 & 29mm saucers, spools etc. are a fun way to accumulate BP.
Rex

#### Bat-mite

##### Rocketeer in MD
I probably went overboard suggesting two e-matches. With motor BU, you don't really need them. But I destroyed a rocket when it core sampled after the single e-match burned thru the heating element but did not ignite the pyrogen. On that flight, the motor's delay was too short, so I had no back-up. But it left a bad taste in my mouth.

#### soopirV

##### Well-Known Member
One other aspect I'm not sure I've seen here- verify that your motor has enough BP to eject safely- you'll have to search online to find the stock charge, but do some calculations to ensure it's sufficient.

#### mpitfield

##### Moderator
Staff member
Global Mod
I used an altimeter with motor ejection for single deploy on my level 1 cert flight. Key is to be comfortable with the function/use of your electronics prior to the flight. If you are, you should be fine. Instructions on-hand and a preflight/pad checklist will help ensure successful prep and flight. Go for it and good luck.

Trey Knox
X2 on this same advice and scenario. I did Stratologger on apogee with motor backup and a cable cutter for main, although my first attempt failed but you can just load it up and do it again. Assuming you have no damage, which in my case I did not just a hard landing due to a tangled main which was enough to fail.

#### rocketsam2016

##### Well-Known Member
Good point and yeah it's plenty for the size cavity I have. 38mm CTI comes with 1.3g. I'll double check though

#### ksaves2

Jim Hendricksen has a post on ematch reliability. Yeah, failures do occur. One can get by with two matches for each charge on a single channel but some electronics might have a problem dealing with the lowered parallel resistance.
If one tests and I guess gets continuity, all should be ok. To have two matches fail on a dual altimetered project would be rarer.
One could use one device that has multiple channels and program for backup on separate channels and use two matches for each charge going to separate channels. Would have to make sure that one's altimeter would be O.K. sending trying to send
current to an open ematch if the first charge was successful. (The backup match would of course burned off after the successful operation of the first match)
When I used to make ematches, reliability was in question and over time I mastered it. The matches actually got more reliable as they aged in storage! With all the options out there now, I no longer construct them from scratch and can speak with
authority they're too much a PITA to make. (ie. I'm talking making the blanks from scratch! I believe the reliable ones go to the ematch makers and the blanks forsale go to the rest of us. I had lousy reliability with commercial blanks.)
The reagents for matches are dicey(er) than those for standard igniters and extra care needs to be used. Again, I gave it up and espouse to others not to bother but had fun refining my technique over 4 years in the winter time while the epoxy was curing on a rocket! Kurt

#### rocketsam2016

##### Well-Known Member
Yeah and I may (cough cough) be buying igniters from Jim for future use (with a Tender Descender and maybe regular charges) . He recommended 2 of his in parallel.

In the immediate term though and for this launch I'm currently planning on using hte pratt ejection canisters which *should* be very reliable as long as you check the resistance (and I'll do that right before flight). The hot part is nicely contained and IIUC you are less vulnerable to chemical bits breaking off. The pratt canisters are 2.8Ohm, so 2 in parallel is 1.4Ohm, so my 2S 20C 460mAh Lipo battery will drive ~6A through two parallel, which is a little scary but probably ok for the altimeter transistors, and the battery can technically handle it. Close enough to the line though that I'd rather them be in series I think if I went that route.

#### blackbrandt

##### That Darn College Student
With regards to ground testing at a launch.... well... I'm gonna stay quiet on that part I have, um, bad experiences with that .

+1 on CJ's ematches. I got some and I love them.

#### OverTheTop

##### Well-Known Member
TRF Supporter
If I were you, I would use the Quantum with motor back-up.
+1 for that if it works in your rocket.

Cert flights are a bit more stressful. If you are very familiar with the altimeter that will not add too much to the stress level. I do recommend to keep things simple for cert flights in general.

For batteries I run small 180mAh 2S cells (from Hobby King) for the altimeter, and individual 120mAH 2S batteries for each igniter. This is for reliability. Some batteries have protection circuits that act like a fuse if the igniter shorts out. If the same battery is running your altimeter or other eMatch you are in trouble. I have been known to run the secondary eMatch from the altimeter battery. That way I just lose logging if it fails. Primary eMatch gets its own battery.

Putting eMatches in series can give a problem if one goes open circuit. Neither will fire in that case. Same thing happens if one fires earlier than the other. Second one has reduced probability of firing.

Unplug your batteries straight after the flight. If you let them discharge below 3.6V per cell they are destroyed. They are quite cheap though.

As someone else has said, make sure you ground-test your deployment.

Good luck!

#### Coop

##### Well-Known Member
Cert how you want to cert. If that is to make it your first usage of electronics, cool! My L2 was... I studied the altimeters and really got into the av-bay construction. I had 2 running redundant and plugged the motor. It worked.

Later!

--Coop

#### OverTheTop

##### Well-Known Member
TRF Supporter
Cert how you want to cert.
What he said. Always take the advice (usually varied!), make your own decisions and make the flight your own.

If it is going to be the first time you use electronics, make sure you speak with a few people that have use the same or similar systems. Sometimes you don't know what you don't know. Sometimes that can make the difference between a good and a bad day...

#### DavidMcCann

##### Well-Known Member
With regards to ground testing at a launch.... well... I'm gonna stay quiet on that part I have, um, bad experiences with that .

Protip #1: don't do it while on the pad.
Protip #2: Don't do it in the parking lot a short hop down from the TRA BOD.
Protip #3: You don't have to use the whole @#%$$% can. Protip #4: Stay clear and block the rocket with something preferably not made of meat. Typically, you can notify the LCO you're going to do one just past the spectator line, away from the pads, and kick it off while people are loading, pointed in a safe direction. #### Nathan ##### ☢ TRF Supporter I have seen all of the following dual-deploy failures (a couple of which I have done myself). If you can avoid these then you have a good chance of success: - Forgot to arm altimeter - Not enough black powder - ejection charge too weak to deploy the chute (yeah I did that) - Battery became disconnected - Av bay wired wrong, main chute deployed at apogee - Main chute packed in lower section instead of in payload section, deployed at apogee (yeah I did that too) #### blackbrandt ##### That Darn College Student Protip #1: don't do it while on the pad. Protip #2: Don't do it in the parking lot a short hop down from the TRA BOD. Protip #3: You don't have to use the whole @#%$$%\$ can.
Protip #4: Stay clear and block the rocket with something preferably not made of meat.

Typically, you can notify the LCO you're going to do one just past the spectator line, away from the pads, and kick it off while people are loading, pointed in a safe direction.
We actually only used 17 grams.

And as to the pad incident, we just wanted to double check we had the right amount of powder. You can never ground test too many times.

#### OverTheTop

##### Well-Known Member
TRF Supporter
My advice is to arm your avionics before the igniter goes in. That way the rocket can't launch unexpectedly and come in ballistic just because they are not armed. Try to avoid that dangerous situation wherever possible.

#### jeff_j_black

##### Well-Known Member
I flew my first L1 and L2 on motor deploy. My next HP flight on a J motor was dual altimeter, dual deploy.