StratoLoggers are available. Get em while you can
http://www.perfectflitedirect.com/stratologgercf-altimeter/ ;
<http://www.perfectflitedirect.com/stratologgercf-altimeter/>
On Mar 29, 2021, at 1:12 PM, Rob Hoegee <hoegee.rob@xxxxxxxxx> wrote:
Hi Everyone,
Regarding the topic of PerfectFlite Stratologgers going in and out of stock.
I managed to just snag one off the PF website thanks to this:
https://uptimerobot.com/ ;<https://uptimerobot.com/>
It’s pretty simple. You sign up a (free) account and then create an alert for
the webstore page in which you have it send you a text or email as soon as the
product page no longer says “not in stock”. Not entirely what this service was
intended for, but it works!
My best,
Rob
On Mar 23, 2021, at 9:25 PM, Cris Erving <cris.erving@xxxxxxxxxxx
<mailto:cris.erving@xxxxxxxxxxx>> wrote:
Dave:
Very interesting, too bad you didn't get the RRC3+ data.
I don't know how PF/MW/Marsa/AM do their Mach auto-immunity, but what
Eggtimers do is to not look for apogee until the rocket's baro velocity is
less that abs(100 fps) for at least one second. That takes care of the Mach
"knee", which is generally nowhere near as gentle as a coast to apogee.
Once that threshold has been reached, we record the highest altitude, and if
nothing higher comes along one second after that then we call that reading
apogee and deployments can begin. There is a fundamental difference between
the Eggtimer approach and some others... they're trying to predict apogee, we
declare it after the fact.
Eggtimer Cris
From: roc-chat-bounce@xxxxxxxxxxxxx <mailto:roc-chat-bounce@xxxxxxxxxxxxx>
<roc-chat-bounce@xxxxxxxxxxxxx <mailto:roc-chat-bounce@xxxxxxxxxxxxx>> on
behalf of Dave Peterson <woshugui@xxxxxxxxxxxxx
<mailto:woshugui@xxxxxxxxxxxxx>>
Sent: Tuesday, March 23, 2021 9:05 PM
To: roc-chat@xxxxxxxxxxxxx <mailto:roc-chat@xxxxxxxxxxxxx>
<roc-chat@xxxxxxxxxxxxx <mailto:roc-chat@xxxxxxxxxxxxx>>
Subject: [roc-chat] Re: PerfectFlite Stratologger CF Altimeters
Cris,
A very good question because the evidence I have for baro Mach inhibit defeat
is circumstantial at best. By hanging, I mean flights that sim around M1 on
longish burn motors; maybe for a couple seconds or more. Yes, asking for
trouble. I have had two flights of this nature deploy apogee early. One with
an RRC2+ in a Squat, which at first looked like a shred. The other with an
RRC3 in a Punisher 4, which zippered after burnout. The RRC3 data log
unfortunately got clobbered before it could be exported. That would have
been much more definitive.
With the Squat there was no obvious drag separation, which you would suspect
with this rocket. Instead a puff of smoke, presumably from deployment, while
still going up. I am not saying there could not have been drag separation, it
just did not look that way in real life or in the grainy video. Collapse of
the glassed airframe seemed unlikely and the AV bay was actually in the fin
can below the forward centering ring. The vent holes were at the top of the
fin can just below said centering ring. Fiberglass nosecone with parachute
and harness pulled out eyebolt, but survived to fly again. The other half
ended up embedded up to the fin can.
<image0.jpeg>
The Punisher 4 on a full L got to about 6000’ before the separation, so it
was pretty much out of sight. There were two shear pins on the booster, so
drag sep just did not add up unless it had something to to with being
transonic. It was disappointing not to be able to get the log, but then I
remembered that Chris Attebery had posted a similar experience with his L3
Punisher 4 along with a funky slow pressure signal that was attributed to a
pressure wave around the camera shroud.
https://www.rocketryforum.com/threads/chris-punisher-4-l3-build.131084/page-5 ;
<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.rocketryforum.com%2Fthreads%2Fchris-punisher-4-l3-build.131084%2Fpage-5&data=04%7C01%7C%7Cd48c5bdec96c49897c3e08d8ee7a23ae%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637521555683641292%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=c0Wk5TTvQ2d%2FAOHT%2F8afgq6maHMxa1GARc%2F%2FaypLDXU%3D&reserved=0>
These flights have been head scratchers to me for some time. There is no
direct evidence of baro Mach inhibit being defeated; like an actual pressure
waveform, so my statement about slow transients is speculation. Still I am
having trouble coming to another explanation. So I suppose the question is
whether the belt and suspenders of an accelerometer Mach inhibit in a
redundant baro + accelerometer setup would make things better, no different
or worse.
Richard,
Yes, the Raven 3 was my first flight computer! Velocity < Vel1 on Main was my
flat spin faux pas. I also have a Marsa, but have only played with it on the
bench. Oh... also have a gyro module ‘cuz... yup, accelerometers are cool.
Embarrassed to say I have done nothing with the gyro though.
On Mar 23, 2021, at 3:54 PM, Cris Erving <cris.erving@xxxxxxxxxxx
<mailto:cris.erving@xxxxxxxxxxx>> wrote:
Dave:
Out of curiosity, what's the longest that you've seen a flight hang in Mach
transition? In all of the near-Mach or Mach+ flights that I've ever seen,
the high pressure/low altitude dip comes on pretty quickly, and although it
may take a few seconds to come back to "normal" the baro-derived velocity in
no way could be interpreted as anything near a coast to apogee.
Eggtimer Cris
From: roc-chat-bounce@xxxxxxxxxxxxx <mailto:roc-chat-bounce@xxxxxxxxxxxxx>
<roc-chat-bounce@xxxxxxxxxxxxx <mailto:roc-chat-bounce@xxxxxxxxxxxxx>> on
behalf of Dave Peterson <woshugui@xxxxxxxxxxxxx
<mailto:woshugui@xxxxxxxxxxxxx>>
Sent: Tuesday, March 23, 2021 3:28 PM
To: roc-chat@xxxxxxxxxxxxx <mailto:roc-chat@xxxxxxxxxxxxx>
<roc-chat@xxxxxxxxxxxxx <mailto:roc-chat@xxxxxxxxxxxxx>>
Subject: [roc-chat] Re: PerfectFlite Stratologger CF Altimeters
Glad to see I am not the only one who obsesses about flight computer
redundancy. Curious to hear what folks think about accelerometers in their
redundant altimeter setups. I used to pair baro+accelerometer with baro
backup, mostly to save $$ and ‘cuz well... accelerometers are cool. The
baro backup saved me from some bad programming decisions; like an
accelerometer inhibiting main deployment in a flat spin recovery. I took
some introspection to realize the problem was not with the way the
accelerometer signal was being processed, but rather with the guy who
programmed accelerometer inhibit main in the first place. After this,
accelerometers were not quite as cool and I migrated to dual baro only.
Usually RRC3+ and RRC2. One of the few frustrations I have had with the
baro only systems is that their Mach inhibit can be defeated if your flight
hangs in the transonic region too long. The pressure transient is just too
slow not to look like apogee. Yeah, I know you are not supposed to hang at
M1, but hey, it happens. So here is my esoteric question. Would a spendy (by
definition) dual baro+accelerometer setup with the accelerometer only used
for Mach inhibit help with the M1 problem on apogee deployment with
redundancy; proving that yes, accelerometers are still cool?
On Mar 23, 2021, at 1:36 PM, Michael Kramer <mike@xxxxxxxxxxxx
<mailto:mike@xxxxxxxxxxxx>> wrote:
One advantage is the cool sounds two different altimeters beeping at the
same time sounds like. If you start them at the right time, an Adept and a
Perfectflite Strattologger sound like the intro to Blue Monday.....
I’m leaning to using (2) of the same altimeters. Here is my logic,
a) A) If there is a more reliable and less reliable altimeter why would
you use the less reliable one even as a redundant one. So – assume all of
them have the same level of reliability.
b) B) Everyone focuses on the non-event, but an ‘early event’ may be
equally bad. If one altimeter has an early event is doesn’t matter what
the second one does, first to fire wins (or causes failure as the case may
be). Having 2 different altimeters INCREASES the chance of an early event
failure.
c) C) To the point being made, having 2 identical REDUCES the chance of
operator error (seems to be the recurring theme). Common operation and
hookups.
d) D) Having identical mounts makes it easy to swap out an altimeter if
it is ‘acting strange’ (assuming a single mount holding both altimeters).
Wires in the same place and same ‘orientation’.
e) E) I haven’t had a failure of a board itself that passed the powerup
test that WASN’T something that I did.
Minor (really minor) concern is the never seen but frequently discussed
‘both altimeters going off at EXACTLY the same time’, you could argue that
two different brands of altimeters would be less likely to have that
happen. I’m not going to worry about that one. I’m more concerned (but
have never seen it) about sympathetic detonation between two charges.
Having said that I do have different altitudes set for the main charges.
Larger charge in the later one?
And yes, totally separate power switches, wires etc.
Mike Kramer
On 3/23/2021 12:07 PM, John Coker wrote:
There's also the human aspect. Is it more reliable to do the exact same
thing twice or two different things once each?
If you have two different alts, with two different status checking
procedures, is it easier to remember that you armed both?
I suppose if you truly use a complete checklist it doesn't matter, but I
for one do not.
John
On Tue, Mar 23, 2021 at 11:55 AM James Dougherty <jafrado@xxxxxxxxx
<mailto:jafrado@xxxxxxxxx>> wrote:
Most of the interesting research in this field was done in the 60's by
NASA during the Apollo program and
falls under the general term of statistical probability and (as it is
applied to computer science)
"fault tolerance" and "high availability". In this discussion it is
important to note that it is not just the quantity and type of the systems
being used, but their relation to each other as being truly independent
with respect to their operation modes within the whole system.
So far the only discussion point has been replication, redundancy and
diversity of flight computers; which
is all valid, however, to be truly fault tolerant we also need to discuss
and consider:
- replication of power supplies - one battery failure (e.g. a 9V battery
holder)
disconnecting should not fail one computer (e.g. parallel/redundant
batteries)
- replication of wiring harnesses - an e-match being severed during boost
shall also not affect the other ematch (e.g. parallel / redundant charges)
- time varying deployment - 2 altimeters both serving an apogee charge
should be time-delayed
to avoid both going off at once and blowing a hole in your airframe.
And every other aspect (switches, batteries, etc). We need to be truly
self-sufficient and independent in our designs to achieve fault tolerance.
Why is this important?
The multiplication rule of probability is only valid if the two altimeters
and their corresponding
subsystems are truly independent. It makes absolutely no sense in all
discussion unless the
systems are independent - whether you use altimeter A or B, it will not
matter unless this condition holds.
Mathematically, we say the conditions are independent if one event DOES
NOT change the probability
of the other event. In doing this, we can multiply the two probabilities
together to form an even more
fault tolerant system.
For example, consider two flight computers A & B with their probabilities
of failure as below:
P(A) = .1 (10 times out of 100)
P(B) = .05 (5 times out of 100)
If the two are independently operating systems (in all aspects), then we
can compute:
P(A) * P(B) = .005 = 5 times out of 1000!
It's one of the *only* free rides you can get in nature!
The opposite end of the spectrum is conditional probability where the
outcome of one event will affect
another - the classical example is the Monty Hall problem and even more
interesting today is the
"Guessing game" where a well versed spectator can "guess" the
numbers/cards of a player
like they are reading minds - it's not a Jedi mind trick, it's math :)
On Mon, Mar 22, 2021 at 7:25 AM Michael Kramer <mike@xxxxxxxxxxxx
<mailto:mike@xxxxxxxxxxxx>> wrote:
not to get all Kevlar vs nylon but...
Just checking peoples philosophy, if you have a redundant altimeter,
better to have;
a) 2 identical ones (Stratologger CF - Stratologger CF )
b) 2 different ones, each from different manufactures (I.E. Stratologger
CF - RRC3)
c) 2 different ones, same manufactures (I.E. RRC2 and RRC3)
d) doesn't matter any combination works
Mike Kramer
On 3/20/2021 11:00 AM, Chris J Kobel wrote:
Richard,
Darn it, left work at 3:30 and missed it! I had the website up and
refreshing and everything.
Thanks for the heads up, I’ll just have to keep trying.
Chris
<>From: roc-chat-bounce@xxxxxxxxxxxxx
<mailto:roc-chat-bounce@xxxxxxxxxxxxx> <roc-chat-bounce@xxxxxxxxxxxxx>
<mailto:roc-chat-bounce@xxxxxxxxxxxxx> On Behalf Of richard dierking
Sent: Friday, March 19, 2021 8:06 PM
To: roc-chat@xxxxxxxxxxxxx <mailto:roc-chat@xxxxxxxxxxxxx>
Subject: [roc-chat] Re: PerfectFlite Stratologger CF Altimeters
Well, hopefully Chris got my email and placed his order. Perfectflite
Direct had CF's in stock for a couple hours. Now showing out of stock
again. :-(
On Mar 19, 2021, at 2:01 PM, Chris J Kobel <chris.j.kobel@xxxxxxxx
<mailto:chris.j.kobel@xxxxxxxx>> wrote:
Thanks Mike and all,
I just might have to try that!
Chris
From: roc-chat-bounce@xxxxxxxxxxxxx
<mailto:roc-chat-bounce@xxxxxxxxxxxxx> <roc-chat-bounce@xxxxxxxxxxxxx
<mailto:roc-chat-bounce@xxxxxxxxxxxxx>> On Behalf Of Mike Riss
Sent: Friday, March 19, 2021 1:46 PM
To: roc-chat@xxxxxxxxxxxxx <mailto:roc-chat@xxxxxxxxxxxxx>
Subject: [roc-chat] Re: PerfectFlite Stratologger CF Altimeters
Chris,
Seems like waiting for SLCF's to become available is like hunting for
snipe ;-)
In the meantime, I'd recommend trying Eggtimer's Quantum. Pick up an
Apogee and a Quark while you're at it.
Mike
On Friday, March 19, 2021, 12:47:18 PM PDT, Chris J Kobel
<chris.j.kobel@xxxxxxxx <mailto:chris.j.kobel@xxxxxxxx>> wrote:
Just wondering, anybody know why PerfectFlite Stratologger CF Altimeters
have been unavailable for so long?
Thanks
Chris Kobel
(looking forward to see you all April 10!)
