Hi Kenny,
Thanks for your comments; I agree particularly that redundant
electronics is the way to go. I wish I had put my RRC3 in there with
the Raven. Instead I had an EggTimer WiFi switch, a new thing I was
trying, but that took up all the extra room. No knock against the
EggTimer specifically here but I found it not useful in this
configuration. While it let me arm the Raven remotely and showed the
continuity on the main & pyro channels, I still had to walk up to the
rocket and listen to the Raven's beeps to make sure it was happy. So,
in retrospect the EggTimer just added circuit complexity but didn't
provide much by way of functionality. I would have been better to put a
2nd altimeter in its place.
A test flight with a smaller motor would also have been a good idea. I
had actually flown this rocket once before on a slightly less powerful
J, but since I had changed the configuration I could have re-tested on
and H or I first. Another lesson learned.
BTW the rocket weighed in at about 145oz with the motor. The base kit
may weigh about 75oz but I had "stretched" it with a 2nd payload bad and
24" fuselage section, and added the T3 GPS, cameras and nose weight.
Add the weight of recovery equipment, epoxy, motor casing and motor and
the total rocket weight just about doubles. So, the projected maximum
altitude per OpenRocket was about 5500 feet, and that's only with a
straight up flight and no wind. As it is the rocket came off the rail
not perfectly straight up, maybe 10 degrees off vertical (a real guess
there, just eyeballing it) and tailed away northwest.
Anyway, I doubt I will ever know what happened to it. I'm still hoping
someone will find it and that the Raven at least will still be
functional, maybe the cameras too, and then I can do some post-mortem.
In the meantime I have my unfinished L3 project and some smaller stuff
to build, to bring out sometime in the fall.
Thanks again for the suggestions
Terry
On 7/22/2019 8:59 AM, Kenneth Harkema wrote:
Hello Terry,
Thought you were on the right track in starting this post/chat up initially ..you had a question and hoped the more experienced could offer some insight - that doesn't sound like 'go fever ' to me.
My read from your flight description is that your bird went up and then straight down .. terminal velocity . The other thing that fits is the main opened at the top and the winds aloft carried it far far away ...my quickee check on thrust curve said over 8k ft was projected with 75oz with 2.3 inch diameter - perhaps an event was just out of sight. Without recovery and some forensics it is just conjecture .
A good call you made was the fiberglass rocket and good electronics . FG will survive when a paper or blue tube rocket will be unusable ie: zipper, motor cato, short delay, drogue only landing . ect. My friend Mark has a T3 and flies it often . Raven is top line too.
Want to mention AZ Wayco here as he is a very experienced flier and when he first flew his min diameter 54 the electronics failed .. he had flight proven electronics and did not try to do redundant electronics in the tight 54 space . So now he does. Since then he has loaded up on the small, but cheaper altimeters like Eggtimer and Statologger CF - and made them fit .
Richard mentioned the comspec, I lost one last month when I was flight testing my new Punisher ..I had a pressure separation just after burn out and it snapped my drogue shock cord top and bottom ..so the comspec and my wildman recon drogue chute have a new home now , far far away. It is my practice to have a 'nominal' flight in bounds or around 2500 ft to see everything work ..my friend Warner starts with the big motor and says it is going to work or it isn't ..no gutz no glory .
You are in good company and I look forward to hearing about your next project .
Kenny
On Sun, Jul 21, 2019 at 10:21 PM Terry McKiernan <terry@xxxxxxxxxxxxx <mailto:terry@xxxxxxxxxxxxx>> wrote:
>> Did you get any position info from your GPS tracker?
Well, here's a case where I took a bad situation and made it worse.
The T3 GPS receiver (i.e. the part attached to my phone, for
tracking) was getting telemetry for a few seconds after launch,
then stopped. I didn't count the seconds to when it stopped but I
think the rocket was past apogee but still in the air. I think it
just got out of range. The rocket did not come off the rail very
straight and while it climbed pretty high, it was tailing away
from the launch area to the northwest. The projected apogee from
OpenRocket was over 5000 feet and since it was going more
parabolic I can see where it would exceed the T3 range. But,
that's OK -- with just the direction of travel I figured I would
just walk towards it and pick up the signal once I got close enough.
This is where I screwed up. Me and my brother-in-law set off
across the lakebed, and after about 15 minutes (about 1 mile) we
still had not picked up any signal. Here comes the blunder. I
have seen a failure mode in the T3 receiver (or perhaps in my
phone or Bluetooth GPS) where the Bluetooth connection to the
HC-06 module on the T3 drops out and so even though Bluetooth GPS
says it's connected, it's not getting any data. So I tapped Stop
to drop the connection, then Connect. No NMEA data stream so I
restarted the T3 receiver to see if it might pair up again.
Nothing doing there so in desperation I restarted my phone too.
Notice the missing step? :) I didn't write down the
last-known-good position before the disconnect/reconnect and the
restart. It was just brain lock, or sunstroke, or something. In
my mind the failure mode was one of connection between receiver
and phone, when in reality it was more likely the transmitter was
damaged. So I lost the last-known-good data. This was entirely
my fault. Now, I am almost certain it was still in the air when
the data stream stopped, so I would not have had the landing
position, but it might have helped.
In retrospect also I regret one design choice for this rocket.
For the T3 GPS you can get either a wire whip antenna or an RPSMA
connector to mount the antenna of your choice. I went with RPSMA
so I could put on a big antenna, maybe even an amplifier. In this
case I used a 5 dBi antenna that's about 18 inches long; I put it
up in the upper fuselage section with an RPSMA connector in the
payload bay bulkplate and a cable to the T3 inside the payload
section. This worked great in at-home testing but has a fatal
flaw. In the case of a crash especially nose-first the antenna
may get snapped off. With no antenna the effective range of the
T3 drops to about 50 feet (I've tested this); not surprising since
it would just be the tiny RPSMA female pin transmitting into free
space. I suspect this is part of what happened -- something gone
wrong in the recovery system, lawn dart into the lakebed, antennna
damaged and thus T3 effectively rendered useless. I expect that
the T3 itself survived; electronics boards are remarkably tough
and I had it "floating" in the bay with some padding and strain
relief on the battery connections, so it could take a really hard
jolt if needed. But, the antenna outside the bay would not have
fared so well.
I think I'll get another T3 since I've been happy with it, but
either I'll get the wire whip antenna, or stick with RPSMA but use
an antenna small enough to fit within the payload bay. I'll lose
a little range but prevent this failure mode.
In hindsight however I should never have flown. When I first took
this rocket out to the pad, despite many tests at home, there was
a problem with the WiFi switch flaking out / dropping connections,
and with continuity to the drogue ejection charge. I took it off
the rail back to my table, took it apart, found a loose
connection, rewired, retested (all good) and then tried to fly. I
should have just stopped and taken it home for more thorough
diagnostics. After all if there was one bad connection maybe
something more systemic was wrong. But, I just really wanted to
fly it since the idea was then to pull out the electronics and use
them in my L3 cert kit, still under construction.
Also in highsight this was not a very good rocket! The only other
time it flew was my L2 cert, and it went up about 2500 feet and
then arced over, landing about 1.5 miles to the south of the
launch pad. The deployment all worked but it was not a pretty
flight. So that's 2 flights, neither of them very straight. I
think one problem is that with this kit you have a long skinny
rocket but relatively small fins at the bottom. With the light
minimum diameter fuselage the weight is concentrated at the bottom
so the stability calibers (or calipers :) ... sorry) is not high
to begin with. I had added 2 camera bays (down and side-facing)
on the outside, but I think I put them up too high. The added
drag moved the center of pressure up and thus reduced stability
further. I compensated with a nose weight and the extra payload
section (made it longer to move up the CG) but that also made it
more prone to flex ... it just wasn't a very stable rocket. I
regret ever getting this kit!
<whining mode = on>
Not a very good 2 months for me in terms of rocketry. In June my
canopy was destroyed by wind (I got a better one to replace it,
with some super heavy tent stakes to hold it down better), and
also I had an LOC Precision 3" Black Brant get ruined when, after
landing, it was dragged by the wind across the lakebed for over a
mile, losing 2 fins and the camera. This month I lost my green
rocket with all the electronics, and for good measure the motor
retainer in my White Wolf did not hold and so I lost its CTI motor
casing. All told about $1000 in lost rockets and equipment, even
before the cost of the motors for the unsuccessful flights. Ugh.
<whining mode = off>
Oh well.
Terry
On 7/21/2019 2:06 PM, Mike Riss (Redacted sender rockt_dude for
DMARC) wrote:
On Sunday, July 21, 2019, 8:35:49 AM PDT, Terry McKiernan
<terry@xxxxxxxxxxxxx> <mailto:terry@xxxxxxxxxxxxx> wrote:
Furthermore the GPS failed (perhaps on impact) and despite
spending a few hours driving around the lakebed
after the launching was done, my son and I never found the rocket.
Terry,
Sorry to hear about your rocket. Did you get any position info
from your GPS tracker? If so, what was the last reported
position, and what time during the flight did it correspond to
(on the way up, somewhere around apogee, or on the way down).
Thanks,
Mike
--
Kenneth Harkema
Mobile: 619-248-4716
