>> 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> 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