Success/failure rates with GPS trackers

[MountainRocketeer]

I am still trying to decide which tracker to order, and I started by reviewing all threads about trackers in this forum. I really would like to use a gps version, but I have heard about people losing gps lock or communication during flight and never recovering their rocket. Of course, there are plenty of stories about folks losing rdf signal when their non-gps unit touches down and then is never heard again. I have been inclined toward the Telemetrum because it offers the best of both worlds. But maybe that is more "insurance" than I really need.

I would be glad for any input you may have:

1. What gps tracker(s) do you use, how much/how long, and how has your experience been?

2. Have you experienced loss of gps lock or tracker communication using a gps tracker? If yes, were you able to rdf it?

3. With gps trackers--particularlt Telemetrum--are you comfortable relying on the gps (teledongle) data alone, or do think it is important to have rdf equipment as a backup?

4. Specifically with Telemetrum, have you had any other problems worth noting? Would you recommend the system?

5. I doubt there is any sort of data available on failure rates or probabilities, but if there is any, I would certainly appreciate it.

[lkal32]

I am on a team that has been using Telemetrums but we have had some problems connecting the computer to them. We have been able to get them to work most of the time, sometimes it is just more of a hassle and we cant figure out why. We also have had problems with them turning off in flight (after the ejection charges thank goodness) and we were told it might be from the shock of the charges.

I dont want to sound like I am bad mouthing them, they really are a terrific product and their abilities to do both deployment and tracking all in one is unique. I dont own any telemetrums personally, so aside from the team using them, I dont have any other experience.

I do own two beeline transmitters and had 2 GPS beelines until one stopped transmitting at apogee (again, i am betting it was from opening shock), but that one was on an altitude record rocket, and things were pretty tight in there. Needless to say I never found that one again.

I would still recommend the telemetrum, especially if you need both altimeter and tracking features. If you already own an altimeter or two that you like, I would suggest the Beeline instead.

You will have some risk of losing your rockets even with GPS, but either unit will (on most occasions and with practice) come in great use.

Oh, and if you are interested in just plain RDF units, like I said I have two beelines and those babies are amazing. I have a Yaesu VX3r, 7 element Arrow Yagi, and an offset attenuator (Arrow as well) and I have never lost a rocket with them. I have even been carrying a rocket back from a corn field (full of corn mind you) and the beeline fell out of the nosecone. Back at the car, I thought all was lost, but I managed to track that baby right back to the square foot where it fell out was was laying under some corn. It will take a little bit more time and effort to pin point them compared to GPS, but boy that can be part of the fun. I have a lot more stories hunting them, but I will simply end it with, I highly recommend the plain RDF 70cm Beelines.

[MountainRocketeer]

P.s. I will be using the tracker in a staged rocket, so I will need to run a Raven in addition to any other electronics I use.

Also, this will go in a 29mm coupler. Does anyone have any experience fitting gps trackers in 29mm airframes?

[troj]

1. What gps tracker(s) do you use, how much/how long, and how has your experience been?

BeeLine and BeeLine GPS; for...geeze...4 or 5 years, at least?

RDF is an art and you'll need time to practice. Put your tracker in rockets that are easy to recover and use them to practice on. Have a friend go hide your tracker in a field, and go find it, when you don't know which direction s/he went.

2. Have you experienced loss of gps lock or tracker communication using a gps tracker? If yes, were you able to rdf it?

Up? Yes. But once the rocket slowed, it reacquired GPS lock.

3. With gps trackers--particularlt Telemetrum--are you comfortable relying on the gps (teledongle) data alone, or do think it is important to have rdf equipment as a backup?

Never used a Telemetrum.

4. Specifically with Telemetrum, have you had any other problems worth noting? Would you recommend the system?

Based on what I've seen of Bdale and Keith and how they support their products, I'll buy one at some point. Like Greg Clark (Big Red Bee), Adrian (Featherweight), John Derimiggio (MARSA) and Jim Amos (MissileWorks), these guys are great at supporting their products.

5. I doubt there is any sort of data available on failure rates or probabilities, but if there is any, I would certainly appreciate it.

My experience has been that if it works out of the box, it works.

Also, this will go in a 29mm coupler. Does anyone have any experience fitting gps trackers in 29mm airframes?

If I remember right, the BeeLine GPS needs a 38mm, but the Telemini will fit in a 29mm coupler.

-Kevin

[cwbullet]

I have used a Garmin Astro for 2 years on larger rockets. I have never lost a rocket. It loosed contact for the boost, reacquires quickly.

[Marsman]

The telemetrum is very feature packed, but also very sensitive. It took me 4 flights and a couple of near losses to get it working properly. It's very sensitive to other electronics and wiring creating RF interference, and is also very sensitive to metal and having lots of stuff in the av bay around it. You should be pretty good keeping it in a reasonably isolated environment though, and if you're careful (the section on the Telemetrum website was developed partially as a result of the issues that I found), you can use it successfully in a more dense environment with other boards nearby.

I'd definitely look at getting a backup RDF beacon though. They're great backups for GPS systems that have a higher failure rate. You can just tape one to your shock chord right before final prep and have some additional peace of mind.

I also want to add that no matter which system (Beeline or Altus Metrum) you go with, both Greg (Big Red Bee) and Keith/Bdale (Altus) are just an absolute pleasure to work with. If you have any issues, they'll be quick to get you fixed up and ready to go again.

[bobkrech]

Inexpensive consumer GPS will loose lock when acceleration exceed 4G or 6G depending on chip set. Lock is usually required quicky once the acceleration drops beliow these limits.

Bob

[bigredbee]

Just a few comments specific to the BigRedBee

- it won't fit inside a 29mm coupler (it's about 30mm wide)
- you can RDF it (it sends a combination of 1200 and 2200 hz tones)
- it will lose lock at launch, but regains lock prior to apogee


And some general comments

- Less is more. I've seen many projects fail because of excess redundancy. Multiple RF transmitters in one ebay is asking for trouble. It might appear to work on the ground, but all of the RF noise may make it impossible to re-gain lock after motor burn out.

- Put the GPS in the nosecone. That's where it belongs if you have space. Not in the e-bay with the altimeter or other transmitters.

- Don't hard mount it. It increases the chances of damage due to shock forces, and rumor has it that the increasef\d vibrations lead to loss of lock. Wrapping in bubble wrap is sufficient (just don't use conductive (pink) bubble wrap!)

TEST TEST TEST

I've never lost a GPS (that didn't bury itself). I've never had to RDF a GPS, and every flight that I've done has regained lock prior to apogee. Of course, my experience is limited to BigRedBee gear.

Greg

[atrobinson]

1. What gps tracker(s) do you use, how much/how long, and how has your experience been?

TeleMetrum 1.2, a few weeks and one flight.

2. Have you experienced loss of gps lock or tracker communication using a gps tracker? If yes, were you able to rdf it?

Telemetry stopped after the drogue deployed, reason unknown. Drogue deployment parted the recovery harness at the connection to the fin section due to a construction error. Main did not deploy, but low altitude flight (177m/580ft) and excessive fin-filleting resulted in almost no damage to either fin or forward sections.

The failure of the main deployment implies that the TeleMetrum lost power, as the untouched main ejection charge was successfully ground-tested after recovery of the rocket (using the "fire igniter" feature of AltOS UI). I was unable to verify power to the Telemetrum on recovery (one of my complaints is that there is no visual indication of power to the device after the POST). Telemetry was never recovered by the ground station until I cycled the TeleMetrum's power switch. Telemetry worked fine after recovery and after I cycled the device.

There are several reasons why power may have been lost or interrupted, including, due to my tight ebay, the fact that the switch is mounted at a 120 degree angle to the thrust axis instead of 90 degrees. The switch has an activation pressure of 330g which might have been achieved due to a drogue deployment charge closer to the "blow it up" end of the spectrum. I plan to move to a rotary (voltage selector) switch or pull-pin switch for my next launch.

3. With gps trackers--particularly Telemetrum--are you comfortable relying on the gps (teledongle) data alone, or do think it is important to have rdf equipment as a backup?

If GPS lock is lost under boost, it will almost always be regained during coast or descent. If the radio is operating and you are receiving telemetry, the GPS position will be a much faster way to find the rocket than RDF (speaking as a CAP pilot who has had to search for "old" 121.5MHz ELTs versus the new 460MHz digital position reporting ELTs). If the radio is NOT working, you won't receive either GPS or RDF information. The only way the RDF will help is if the GPS fails entirely but the radio is still working--and that seems like an outlier case to me, though I have no data to back that up.

4. Specifically with Telemetrum, have you had any other problems worth noting? Would you recommend the system?

I love the Telemetrum from a design and philosophical point of view, and Bdale and Keith have been great to me as an overly enthusiastic FNG. My launch population of one with this device is insufficient for me to give an empirically-based thumbs up or thumbs down. This flight (a modified Aerotech Mirage, my second rocketry project in 30 years) did raise some concerns about the robustness of the device. My rocket is big and heavy for the motor I'm using: 85" LOA and >4lbs (very close to the minimum thrust-to-weight ratio for a G75J). This was intentional on my part to keep the speeds, accelerations, and altitudes low for initial flight tests. The maximum acceleration reported by the Telemetrum was 80fps (2.5gs) and the maximum speed around 180fps (less than 135mph). The drogue ejection charge was too big (between 1.7-2g of 4F) but not so big it should have caused a power interruption, even with the eccentrically mounted switch.

BTW, a TeleMetrum costs $225, not $300, to replace--and most of the altimeters I've seen with any data logging and transfer capability cost north of $100 for much, much less functionality. Also, as a 32-year software engineer and UI designer, I despise beeping and blinking as a way to convey information other than "I'm alive." So based on aesthetic and engineering principles I will continue to work with the TeleMetrum. Based on my interactions with Bdale and Keith I believe they will stand behind the product.

[atrobinson]

I am on a team that has been using Telemetrums but we have had some problems connecting the computer to them. We have been able to get them to work most of the time, sometimes it is just more of a hassle and we cant figure out why. We also have had problems with them turning off in flight (after the ejection charges thank goodness) and we were told it might be from the shock of the charges.

What kind of problem? I had problems under Windows 7 where a Telemetrum connected directly by USB to a USB 3.0 hub would not be properly detected, where one connected to the computer's native USB 2.0 ports worked fine. Now I just connect the devices directly to the native USB 2.0 ports. Once I got that bit sorted I've never had problems with the TeleMetrum or TeleDongle subsequently, either direct-attach or for telemetry/remote control.

[stealth6]

My experience is not extensive, but for what it's worth....

I own/fly a BRB900 with handheld receiver. It's got a couple dozen flights so far. Works great.

It has never failed to work, and I've found my rocket every time I've used it. I use an old Garmin Etrex handheld to navigate, and I always walk to within about 30' or so from the landing spot. As far as losing lock during boost - I guess it does, but I'm generally watching my rocket at that time, so as long as it regains lock by apogee (which it always has), no problem. I don't use it for analyzing flights or anything like that - for me it's just "where is my rocket?" after the flight. And for this it seems like a fantastic product, that I've very confident in using.

Downsides? - well, first of all it's not exactly tiny/lightweight, at least not comparable to a lot of RDF trackers. This is no big deal for larger rockets, but if you want the absolute lightest/smallest unit available, this is not it. Mind you, it DOES fit in minimum diameter 38mm rockets, so it is still remarkably small in the greater scheme of things. Also, I find the antenna mount a bit skitchy. There are three types - a thin/tiny flexible antenna, a hard mounted "rubber duck", and a short flexible mounted "rubber duck". I use the third option, and the antenna itself is so much heavier/stiffer than the flex cable, that it tends to pull itself out of the unit. I've rigged up a way to keep things secure, but I'm not thrilled with it. The hard mounted antenna is also apparantly prone to damage as well. The smaller first option seems less likely to be damaged, but it has less range. I'm not sure what the best solution really is, but each of the three options have their issues.

Back to the plus side - the support from BRB is excellent. Greg is very good with his customers.

All said, I'm very comfortable recommending this unit to others, and I've been happy with my purchase.

s6

[FredT]

I've been flying the TeleMetrum for two years. Previous to that I've flown GPSflight and Ozark GPS. I find the TeleMetrum vastly superior to either of those, but not perfect. Both GPSflight and Ozark use 700 MHz spreadsecturm for telemetry. I've found that to be unacceptably unreliable... lost telemetry on for the 50% of the flights.

I've had more than 30 flights with the TM. Unfortunately I 've experienced issues similar to that reported by atrobison. The cause is not that the TM lost power in flight, but rather the altimeter reset during the apogee deployment event. According to Keith and Bdale, this is caused by momentary electrical spike from deployment firing leaking back into the RF sub-system causing a voltage glitch which resets the microprocessor. I've had this happen at apogee and main deployment. After the TM resets and regains power, it's a crap shoot whether its in "flight" or "idle" mode. The telemetry protocol is deferent between thses two and if your reciever is in one and the on-board unit is in the other, you loose telemetry. If you're lucky the unit will reset to "flight" mode and you'll get lat and long to find your rocket, but if the reset occures at apogee, you will not get main deployment.

Because of the way I configure my e-bays, I tend to have this problem more at main deployment than apogee, which is a good thing since you've had full deployment and even if you don't regain telemetry, you have a very good idea where your rocket landed. Still, the fact that this can happen is not a great confidence builder.

Keith and Bdale say that twisting lead together can greatly reduce if not eliminating in-flight resets. My experience confirm this claim. I am careful to make sure all the wire runs within the e-bay are twisted around each other. This includes the wire runs for the deployment charges, on/off switch, and battery. With proper flight prep, I've achieved 100% success with the TM. Unfortunately, it took a handfull of failures to get there.

I always fly myTM with another altimeter (usually a Raven) and I use the TM as the primary because I always use a little more BP for the backup charges. I also am careful to twist the wire runs for the backup altimeter as a precausion, but I've never had a case where a spike the a backup deployment reset the TM.

I am pleasently surprised that it seldom looses GPS lock in-flight. I typically boost between 10 and 15 Gees, at speeds as high as Mach 1, and multi-staged. The few times it did, it quickly regained lock. When everything works, it gets me to within 30 feet for recovery.

I've run TM software under Vista, Win7 and Win8 on desktops and laptop. The one time I had a problem I fixxed by getting into the Device Manager to delete the associated device driver then re-installed TM software. Just re-installing the software didn't do the trick. I attribute this problem to Windows, not TM.

All said, I am pleased with my experience with the TeleMetrum and would recommend it to others, but with the above caveats.

...Fred