[roc-chat] Re: using motor ejection charge as backup?
- From: R Dierking <applerocketry@xxxxxxxxxxx>
- To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
- Date: Tue, 23 Jul 2019 13:56:42 +0000
I should look into BRB myself. I started using the CommSpec type when that’s
just about all there was. Then, people started using dog collar GPS trackers,
and it’s developed into what many people are using today. So, the CommSpecs
are probably old school tech. And, just like using GPS, CommSpec directional
tracking takes practice and things like reflection will drive you crazy at
places like Black Rock.
So far, the only thing I’ve used so far that has caused me no problems is the
RealFlight system. The description of the flights using RealFlight is cool:
http://realflightsystems.com
And, of course there is the “Kate” system from Multitronix. If you haven’t
seen it, check out this onboard video to 118 K’:
https://www.multitronix.com/118k-flight.h
I’m a bit fat with electronic gizmos at the moment and need to use the
FeatherWeight GPS system I purchase before trying something else out. It would
be cool if David Smith would do a rocket tracking presentation at ROCstock.
Every time I get the chance to chat about this stuff I learn more.
Richard
On Jul 22, 2019, at 9:54 PM, Terry McKiernan
<terry@xxxxxxxxxxxxx<mailto:terry@xxxxxxxxxxxxx>> wrote:
Interesting, thanks David! I'm looking at their site now. 70cm transmitter
beacon for only $59, probably about $100-$120 total if you go higher power
(100mw) plus antenna etc. That's certainly a good price, and the range of 5
miles on the ground / 180 miles in the air is impressive. I'll keep this in
mind.
Terry
On 7/22/2019 11:23 AM, David P Smith (Redacted sender dave_w6dps for DMARC)
wrote:
Terry,
Big Red Bee makes a great little tracking transmitter. It is 70cm and uses a
normal type of modulation, so you can use much cheaper receivers. I don't
recommend Communications Specialists, for a number of reasons, particularly the
cost and limitations of the proprietary receiver.
My two cents, to save you $200...
David P Smith
ROC Board of Directors
NAR 78668, TRA 15803, L2
Amateur Extra, W6DPS
http://www.qsl.net/w6dps<https://eur04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.qsl.net%2Fw6dps&data=02%7C01%7C%7Ce077851719204965394408d70f29d1f7%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636994544604867753&sdata=rK5cC6%2FN3jKa33Cd%2B0TaJAVe5ALkNmTKUkPWLz5MGO8%3D&reserved=0>
On Sunday, July 21, 2019, 11:29:48 PM PDT, Terry McKiernan
<terry@xxxxxxxxxxxxx><mailto:terry@xxxxxxxxxxxxx> wrote:
OK, thanks Richard. I'm not familiar with CommSpec but I'll look into it.
Terry
On 7/21/2019 11:00 PM, R Dierking wrote:
So, I pretty typical rocketry experience.
Sorry about what happened really. If you will be considering a new rocket I
can suggest one. With just about any GPS for rocketry a CommSpec tracker is
always a good backup. They will transmit for days and many people receivers.
I continue to wonder what’s going on with the way some rockets are taking weird
flight paths of the launch pad.
Richard
On 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
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