2.6 and 3" birds, do you always run dual altimeters?

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Purely anecdotal, but I have never seen a commercial altimeter fail.
I've been failures that are all user induced or could have been eliminated with just a little ground testing...cheap battery, underpowered battery, cheap battery connectors, incorrect programming, poorly secured battery, undersized ejection charges. The list goes on, but the common trend is user error.

+1 to all this ^

Even after some hard landings and water landings, my altimeters continue to work just fine. I always ground test them after such events. They are surprisingly robust devices.

If you don't know the root cause of bad deployments, then you are potentially doing the wrong thing twice with two altimeters. More altimeters = more complexity = more design time = more prep time. Not worth it for my model rockets up to 4" and a couple hundred dollars. Maybe if I build a big, expensive project, I will change my tune.
 
Purely anecdotal, but I have never seen a commercial altimeter fail.
I've been failures that are all user induced or could have been eliminated with just a little ground testing...cheap battery, underpowered battery, cheap battery connectors, incorrect programming, poorly secured battery, undersized ejection charges. The list goes on, but the common trend is user error.
I've had a few. Raven 1 23rd flight in EZI with J500. Ballistic recovery, completely destroyed. Formula 98 on K160 and Raven 2 4th flight. Ballistic recovery, was able to solder wires to power pads and get data. Never detected liftoff. Motor provided over 5 g's for at least 5 seconds. 7.5" Goblin on Rx L750 and Strattologger CF. Ballistic recovery, was able to get data from altimeter. Intermittent power during burn of sparky motor, then lost power completely shortly after burnout. Hold up cap lasted until shortly before apogee. 9V snap was off the battery and not mashed like the battery.
I fly one altimeter except in high performance rockets. The Cloudbusters were before electronics and used motor ejection.
 
I've had a few. Raven 1 23rd flight in EZI with J500. Ballistic recovery, completely destroyed. Formula 98 on K160 and Raven 2 4th flight. Ballistic recovery, was able to solder wires to power pads and get data. Never detected liftoff. Motor provided over 5 g's for at least 5 seconds. 7.5" Goblin on Rx L750 and Strattologger CF. Ballistic recovery, was able to get data from altimeter. Intermittent power during burn of sparky motor, then lost power completely shortly after burnout. Hold up cap lasted until shortly before apogee. 9V snap was off the battery and not mashed like the battery.
I fly one altimeter except in high performance rockets. The Cloudbusters were before electronics and used motor ejection.
Not to discount your failures, just looking for clarification...

Never used the Raven 2, was it baro armed it accel armed at launch? Possible failure to detect launch due to improperly sized vent holes?
Strattologger sounds like the battery disconnected in flight since the batter clip wasn't smashed, would you agree?
 
Not to discount your failures, just looking for clarification...

Never used the Raven 2, was it baro armed it accel armed at launch? Possible failure to detect launch due to improperly sized vent holes?
Strattologger sounds like the battery disconnected in flight since the batter clip wasn't smashed, would you agree?
Ravens use the acceleration to detect liftoff. IIRC, 3 g's for at least 1/2 second. I did have the apogee detect set to barometric.
Yes, the Strattologger failure was due to battery disconnect. First time I had flown it on a large sparky motor. I now tape the clip on to the battery to prevent this.
 
With recovery being controlled by an altimeter, and smaller birds like 2.6" and 3" birds do you always use dual systems, or are you comfortable with a single proven altimeter?

First of all, whatever you decide, If possible I would consider making the altimeter(s) dedicated to the rocket. Basic dual event altimeters are about $50 a pop, in most cases, cheaper than a quality parachute.

For rockets in the 2.6 to 3" range, I would use a single unit with motor back up (if relevant), unless the you are planning extreme altitudes, then a dual altimeters would be a good fail safe option (not read as fool proof). And to, I would add a tracking system for a rocket flown to higher altitudes where visual tracking is limited.

There are some good 3D printed options for AV bays; two 54mm sleds w/ battery holders should fit inside most 2.6" couplers Maybe not an Aerotech kraft tube coupler). Have a look at Additive Aerospace for 3D printed options.
 
Haven't read the rest of the posts, but I did dual on a 3" that I flew Memorial Day weekend, mostly because it was a challenge to shoehorn two altimeters into that small space. Fun challenge, it worked, and everything flew great.
 
I usually only use one altimeter on 3" or less, but I do have one 3" w/54mm MMT that has dual. Actually, I have some 4" with single altimeters.

I've been flying altimeters since '07 and I'm still not convinced that dual altimeters are really needed on anything short of L3, but I think it's an individual choice.
 
My personal view is that altimeter redundancy should be practiced in all rockets unless there is a really good reason such as (1) it cannot fit or (2) there is something really special about the flight like it is an altitude record attempt and the mass/space reduction is worth the risk, or perhaps (3) you simply cannot afford the extra $50 for a backup.

The reason for this is purely safety. I don't care if the rocket is inexpensive, small, or staying at a low/visible altitude. It can still make a hole in someone. Ballistic rocket scare the crap out of me. I had the pleasure of being about 400 feet away from a 3' minimum diameter K powered rocket come in ballistic. It makes you think. Small makes the rocket much more difficult to spot when it is coming in at the flight line ballistic. Low/visible altitude makes it more likely that it will land in a smaller radius containing the flight line. There will be many persons on the flight line who will not have success at jumping up, locating the rocket, and moving out of the way when/if they hear an announcement that the rocket is coming in hot.

For general flights not violating the the three above principles, why not include redundancy? As others have pointed out above there remains a small percentage chance of a problem with an igniter or computer or intermittent wiring problem such as short or open-circuit. I personally also like to have a backup charge that is 25 to 50% larger than the primary charge in case the deployment is being hampered by friction.

For flights with main at apogee I often use a single flight computer configured for redundant apogee and a separate charge attached to both apogee and main. The computer is not redundant, but everything else is.

I do not like motor deployment as a backup (or primary). The delay time can have significant variability causing zipper/recovery separation by being either early or late. Lately I have been flying rockets where the time to apogee is much longer than available motor delays so it isn't even a consideration.

Here is a link to a stock 38 mm diameter 6" long ebay in which I put fully redundant dual-deploy with GPS and independent batteries, without it being a real pain to use. It took some effort to build, but for me that is actually part of the joy of rocketry.
 
It seems strange, but series is the best. Professional fireworks do it this way. Also, if using LiPos, which have low internal resistance, the added resistance of matches in series will prevent overloading the current to the output channels (Most altimeters are not properly designed to use LiPos). There are many threads on this topic, and some guy learned the hard way and fried his altimeter with a bad combo of Lipos and parallel matches.
Hadn't thought of that... I'd been wiring in parallel in analogy to cluster motor ignition, which of course doesn't apply. That would certainly make life easier on my Stratologger CF (which complains about overcurrents after every launch, but hasn't failed... yet).
 
Series vs Parallel may have more consideration and options:

Series would be best if your primary goal is to have a high resistance load that prevent overloading of the output channel. Series may not be best to ensure deployment because one single open-circuit anywhere in the igniter loop will prevent any igniter from firing.

Parallel does run the risk that one single short may prevent any igniter from firing. To some extent this also exists in series.

Parallel can be implemented using low resistance high power resistor to protect the electronics. A 1 ohm resistor that is 5 or 10 watts would be plenty. Even a 1 watt resistor should work. The implementation is resistor goes in series with the parallel igniter bundle.

Personally I haven't ever implemented either.
 
I once had a thought that I never tried and more or less dismissed:

What if there were a section of green cannon fuse between the primary and secondary charges? If the primary charge wasn't enough and the secondary igniter had a failure then the fuse would light the secondary charge. Green fuse from the end of a surgical tubing charge...

I like simple things and this definitely violates the KISS rule. The smidgen of extra safety would probably be taken away by the added complexity.
 
Hadn't thought of that... I'd been wiring in parallel in analogy to cluster motor ignition, which of course doesn't apply. That would certainly make life easier on my Stratologger CF (which complains about overcurrents after every launch, but hasn't failed... yet).

Same here. I didn't like the warnings from the SLCF, so I went on a mission to add some resistance to my deployment channels. The saga is here:

https://www.rocketryforum.com/threads/exceeded-6a-firing-current-on-slcf.156675/
 
All my HPR flights have had at least two altimeters. My normal setup has the TeleMega in the NC for the drogue events (single altimeter, but two charges on separate channels) and then two entirely separate Ravens to push the main out. So the main is guaranteed to come out, even if the NC did not deploy the drogue. Main charge(s) will shove the NC off and the chute out.

It is important to make sure the airframe doesn't come in ballistic all the way to the ground, for the safety of everyone around.
 
My guideline is simple. If I can make two altimeters fit, I use two. The last time I used one in a three inch rocket (Wildman Darkstar), I left the powder out of the motor because the delay wasn’t long enough. The drogue did not come out and the main shredded when it opened. I took a nice 3” core sample of the salt flats. Lesson learned.
 
We always fly with redundant altimeters (usually eggtimer quantums) and a GPS on all stages. We may have to make an exception for a 24mm 2 stage that won't fit two altimeters :(
 
My guideline is simple. If I can make two altimeters fit, I use two. The last time I used one in a three inch rocket (Wildman Darkstar), I left the powder out of the motor because the delay wasn’t long enough. The drogue did not come out and the main shredded when it opened. I took a nice 3” core sample of the salt flats. Lesson learned.

The real lesson to learn is why didn't the drogue come out?
 
The real lesson to learn is why didn't the drogue come out?
You’re right. More than one lesson. The altimeter was a mess, a couple of feet into the salt, so the failure investigation didn’t provide any lessons. My guess is a loose wire or a bad ematch. So I am much more careful with both.
 
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