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FredA

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Seriously

Looking for the right solution for apogee detect for a flight significantly above 100k.
What is the recommended flight avionics....that's affordable.
Not going to spring for an unlocked GPS.

Keith at Altus Metrum says NoGo for his products.
Most baro-based products aren't sensitive enough for much over 100k.
Accelerometer based integration will be too dependent on perfectly vertical flight.

Anybody have a [preferably proven] solution???
Need something for Balls-26.
Planning a 2-stage where BOTH stages will exceed 100k AGL.

FredA
 
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Handeman

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Fred, that sounds like an amazing flight. I don't have a clue what you would use. I also think it is so far above and beyond what folks here fly that I would be surprised if anyone as a "proven" solution for you. You might need to track that down on other forums, but certainly post back here what you find. I'm sure I will never have a flight like that, but it would be nice to know how.

Good Luck
 

Kip_Daugirdas

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I followed Jarvis' lead on this, it made the most sense. Used a timer for a nominal flight (requires good simulation). And had baro apogee on a different channel spliced into the apogee ematch incase the flight has an issue below 100k.

I was a few seconds early of apogee on my flight. But on a 100 second ascent that doesn't matter much.
 
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FredA

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track that down on other forums,

What other forums???
Seems like this one is the one that has the widest audience.
I don't know of any aimed at higher power.... clue me in if there is one....
 

FredA

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Was hoping for something better than a timer.
Sims become questionable for this type of flight.....
Looking at a 10-second "R" staging to a "N" with a 15-second burn time.
We're talking seriously thin air....
 

Kip_Daugirdas

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Was hoping for something better than a timer.
Sims become questionable for this type of flight.....
Looking at a 10-second "R" staging to a "N" with a 15-second burn time.
We're talking seriously thin air....
I think you will be seriously okay with a timer. Thin air is on your side if you are a bit early or late. I know the RDAS has been used on UP Aerospace flights with success but I'm sure there's some error. Most old sounding rockets used a delay squib (timer) to deploy chutes/sep. payload section.
 

Handeman

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track that down on other forums,

What other forums???
Seems like this one is the one that has the widest audience.
I don't know of any aimed at higher power.... clue me in if there is one....
I don't follow any, but I assume there are some for the amateur rocketry folks, like this one https://www.reddit.com/r/rocketry/ I haven't delved into it, but you might get some answers there. Or ask these folks https://www.friendsofamateurrocketry.org/Home.html

Most of the rest of the sites I've found have a last post of 2011 or 2012 so they wouldn't work.
 

FredA

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Most old sounding rockets used a delay

I think they also had better sim's driven off of wind-tunnel based Cd measurements.
 

UhClem

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At that altitude, being off by even 10's of seconds will matter almost not at all for your recovery system simply because the air is so thin.

An altimeter with a good integrated acceleration algorithm, like the RDAS, should be more than good enough. See the report from the winner of The Carmack 100K prize for more.
 

FredA

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David - is that report posted somewhere on a non-pay site?
 

UhClem

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David - is that report posted somewhere on a non-pay site?
It used to be on the Aeropac web site but my Google-fu must be on the fritz because I couldn't find it.
 

cerving

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How about a Magnetic Apogee Detector? It theoretically shouldn't be too bothered with 100K. If they're still available, that is...

Failing that, how about a 9 DoF IMU?
 

OverTheTop

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How about a Magnetic Apogee Detector? It theoretically shouldn't be too bothered with 100K. If they're still available, that is...
That could work. It might be a problem detecting actual apogee with a simple MAD as they were originally only single axis. It depended on the direction of the rocket as to how far from vertical (magnetic field line are at an angle to the ground) it would trigger. The newer ones have three-axis magnetometers and if the firmware is clever enough it can work out how far off vertical it is. Not sure if any of the existing rocket avionics has that facility.

That still doesn't get you absolute apogee if it flies really vertical and does a backslider...
 

tab28682

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Most old sounding rockets used a delay

I think they also had better sim's driven off of wind-tunnel based Cd measurements.
Years back, I remember reading that a number of sounding rockets used two timers, figuring that figuring that one timer is probably 98 to 99% reliable, so two would be 99.6 to 99.8% reliable.

But, as you said, they likely had great data, improved over time by tracking the flights and getting even better numbers.
 
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NateLowrie

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I second Cris' suggestion of using a 9 DOF IMU. The only problem is that there isn't a ready commerical off the shelf unit you can just plug and play. There are 1-2 altimeter development efforts that utilize an IMU but those efforts are still in alpha an at least a year away from something stable enough to consider.

With the number of people pushing past 100k it's a project that needs to happen soon.
 

FredA

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The only problem is that there isn't a ready commercial off the shelf unit ...

Ah, that's a big problem.
We're not about to undertake that design challenge as well as build the rocket....
Need something that isn't vaporware.

This is likely a one-of flight.
With approximately 180 pounds of propellant, it's not something we're going to fly much.
Also expect the booster tube to be single-use....will be lucky if it is still round and straight after it returns.
 

cerving

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The only problem is that there isn't a ready commercial off the shelf unit ...
Really? Wow... IMU's are like potato chips nowadays, you'd have thought somebody would have come up with one by now. (Hint: It's not gonna be me, sorry Eggfans).
 

Bat-mite

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Crazy idea ... check in with Deb K. at Tripoli HQ and see if she can't point you at anyone who has done this in years past. I would have to think that there is someone out there who has the right knowledge.
 

tfish

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I think a timer..if any have a long enough delay...would be the best option for how higher you're planning on going. Watch a few (?) ..not sure how many there are...100K videos. There is so little "air" at that and above altitudes...that having a late (better then early, for altitude achieved reasons) deployment is not going to really matter. The air is so thin it won't even inflate drogue chutes. You can say you did not do any deployment because of that and even be the first to fly a three step deployment. No deployment at apogee because no reason to because of the thin air. And no reason to push your deployment charges/methods at that ridiculous altitude! We waited for (pick a number) 70K to start the actual deployment events. The big thing is not to go early, as to get the highest GPS lock/ altitude as possible!

Tony
 
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cerving

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<plug>FYI, if you're going to use a timer, an Eggtimer will fire a drogue up to 200 seconds after launch detect. I don't know how long it's gonna take you to get to 100K, but I'm guessing it's somewhat less than that.</plug>
 

heada

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I thought most GPS systems would report dropped sat lock if velocity was greater than (from memory) 200mph, which you'll obviously exceed on boost. Once you drop below the cut-out velocity, you'll regain GPS lock and start reporting alt again. Since you're only asking for apogee and not complete flight tracking, you shouldn't need an unlocked GPS and go with an off-the-shelf GPS solution.
 

FredA

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Wow how quickly we (I) forget.
Thanks for the reminder about Derrick's flight.
Don't know how I forgot about that one since I was there when it flew.....

RDAS might do for the booster, but the sustainer needs something that will work much higher.

Will contact James - thanks for the pointer.
 

Worsaer

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I thought most GPS systems would report dropped sat lock if velocity was greater than (from memory) 200mph, which you'll obviously exceed on boost. Once you drop below the cut-out velocity, you'll regain GPS lock and start reporting alt again. Since you're only asking for apogee and not complete flight tracking, you shouldn't need an unlocked GPS and go with an off-the-shelf GPS solution.
I flew my L3 project last month with a GPS-1 and never lost lock, up or down, with a max velocity of 1,300 fps. Not all GPS product are the same - the limitations are often imposed intentionally in the firmware, (inconsistently), and not a limitation of physics.

Here's a quote from one manufacturer:
"In GPS technology, the phrasing “COCOM Limits” is also used to refer to a limit placed to GPS tracking devices that should disable tracking when the device realizes itself to be moving faster than 1,000 knots (1,900 km/h; 1,200 mph) at an altitude higher than 60,000 feet (18,000 m). This was intended to avoid the use of GPS in intercontinental ballistic missile-like applications. Some manufacturers apply this limit literally (disable when both limits are reached), other manufacturers disable tracking when a single limit is reached."
 

Kip_Daugirdas

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I'm going to argue that a timer will suffice. Unfortunately, at the moment, that is the only piece of commercial hobby electronics that will. I know the RDAS flew in UP aerospace's rocket. What it was used for I do not know. Perhaps someone else knows?

I will be flying to 150k again next summer in the same rocket and using a timer setting for deployment above 100k. On this year's flight, the apogee timer charge and backup did not fire on the Easy Megas due to documentation error on Altus' part. That has been fixed. Despite the poor documentation, they are a very versatile flight computer. I recommend them. I used a Beeline 70cm 100mw GPS for tracking. In regards to lockouts, it stopped logging positions above 500m/s.

Video:
https://youtu.be/yhheMOxiLCY

In the video you can hear the timer setting chirp once and the backup a second or so later. The simulation was 20k ft off. But it would not have mattered if I deployed 15 seconds earlier or later.

Air pressure at 100k is 1% of what it is at sea level. So the effect your drogue has at 100k is ~1/100 of what it's going to do at sea level at the same velocity.

Another example of this is from Armadillo aerospace. They used a ballute (supersonic parachute) which deployed at an apogee of 95km. The rocket simply accelerated until it hit substantial atmosphere. At that point it was traveling so fast that when it reentered it stripped the ballute despite already being deployed.

https://youtu.be/Aw11NFz14sA

So exact deployment timing isn't critical.

-Kip
 
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JimJarvis50

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Keith at Altus Metrum says NoGo for his products.


FredA
Fred, did you ask Keith about using the tilt function for apogee detection? Obviously, those units are 9 DOF IMU's with tilt calculated and a pyro output. What's not to like? The only issue, it seems to me, is gyro drift on a long flight. However, my experience is that when the rocket starts arcing over, the transition to horizontal is pretty obvious. I don't know if you're planning on spinning this rocket, but that would likely be a problem as well. You might combine this with a fail-safe timer.

Jim
 
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