Interested in cheap GPS trackers?

Discussion in 'Rocketry Electronics and Software' started by Eric Jimenez, Feb 28, 2019.

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  1. Feb 28, 2019 #1

    Eric Jimenez

    Eric Jimenez

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    Hello! I am new to this forum but not new at rocketry. I searched around the site but just could not find something like this. Pardon me if I might have missed it or if its the wrong place to post this.

    After investigating the different methods of tracking for my level 2 rocket, I came to the conclusion that there wasn't any cheap GPS trackers readily available. All I could find was trackers in the $200 to $400 range. Any cheaper than that yielded sim card trackers which is something that is not preferable. Knowing this I just decided to make my own. I built a 915 MHz tracker for under $50 and it worked beautifully albeit a bit bulky. It went in a 4 inch bay so that wasn't an issue. The rocket landed about 6000 ft away (very windy morning) and the tracker pointed straight to it.

    After my little adventure I wondered if I should make and sell cheap GPS trackers for people since I couldn't find any. So my questions are: would anyone be interested? Is it even a good idea? What would your ideal price be? Has anyone come across a GPS radio tracker (915 MHz) for under $100, maybe under $50 too?

    I was thinking of having a super basic tracker, and a "fancy" tracker.

    The basic tracker would just include a small (could fit in a 29mm) transmitter with an altitude sensor, and a handheld receiver with a small screen that prints out the coordinates, signal strength, altitude, distance and bearing of the rocket in relation to the handheld unit.

    The fancy tracker would have the same transmitter with a bigger antenna. The "fancy" handheld receiver will have the same features as the basic but with a much bigger screen (touch capable) and Bluetooth for phone connectivity (thinking of having a satellite view of the location of the rocket). The housing for these would most likely be 3D printed out of ABS or PETG.
     
  2. Feb 28, 2019 #2

    Cnorm

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    I think you'd get a lot of interest in your system.
     
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  3. Feb 28, 2019 #3

    solid_fuel

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  4. Feb 28, 2019 #4

    DaveW6DPS

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    The cheapest I have seen for a ready to fly tracker is about $200.
    Byonics has one for about $100, but it doesn't include the GPS module.
    You can assemble one from individual modules for well under $100.

    Of course this is only the tracker. A receiver is separate. If you have a smart phone you can put together a receiver system for less than $30. All this assumes ham radio APRS.
     
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  5. Feb 28, 2019 #5

    Nytrunner

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    I'm listening

    Missileworks T3 is $150 for GPS/tx and rx/bluetooth pair. Then there are the Eggfinder products that require soldering
     
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  6. Feb 28, 2019 #6

    BLH

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    You can make a GPS tracker and receiver with handheld unit and screen not requiring a cell phone for under $50!!! Don't the parts cost more than that? Is this assembled or is it the solder together kind? Does the receiver have a enclosure?

    I don't like solder together stuff and would rather pay someone for that part. When I solder, I always figure the bigger the glob, the better the job.

    Remember in 900MHz band there are limits of how much data and how often it can be transmitted to comply with FCC guys rules unless frequency hopping is incorperated...
     
  7. Feb 28, 2019 #7

    DaveW6DPS

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    In any case if it is a 900MHz product it requires FCC certification for both the transmitter and receiver, unless it is a kit assembled by a licensed ham.
     
  8. Mar 1, 2019 #8

    vance2loud

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  9. Mar 1, 2019 #9

    cerving

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  10. Mar 1, 2019 #10

    Eric Jimenez

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    Thats a good point. I have little knowledge about the legality of selling something like this. Would you mind if you were to point me in the right direction to do this right? If there is no way around an FCC certification this idea may go nowhere since I dont have the funds for it.
     
  11. Mar 1, 2019 #11

    Eric Jimenez

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    Thats right! The parts are relatively inexpensive by themselves. I planned on having it fully assembled and enclosed.

    Thanks for the info, I havent thought about that. I'll have to do more research to see if its in compliance with FCC rules.
     
  12. Mar 1, 2019 #12

    Eric Jimenez

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  13. Mar 1, 2019 #13

    DaveW6DPS

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    This lays out the basics.
    https://www.metlabs.com/wireless/6-...testing-certification-of-electrical-products/
     
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  14. Mar 3, 2019 #14

    Eric Jimenez

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  15. Mar 12, 2019 #15

    ksaves2

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    The problem with these devices, is if you can't call them or they you, your totally sight unseen flight will be lost.
    A device the gives a constant telemetry stream to the limit of range is a smarter option as the positions cn be saved and there is the option of live tracking on a map without Internet access. Your rocket goes out of radio range, you have a drift trend and know where to start the search. You pays her money and takes her chances. Kurt
     
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  16. Mar 12, 2019 #16

    Eric Jimenez

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    I have mine set up to just keep sending it's position whether there is someone looking for it or not. If it's out of range you'll get a general idea of where it's at and once you get close enough it picks up it's signal again. Is that what you mean?
     
  17. Mar 13, 2019 #17

    ksaves2

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    Problem is, is if you have absolutely no idea where it went and don't have the last coordinates you're on a blind search. How often does it send it's position? Obviously, these things can work well as an assist device if you see the rocket come down in vegetation. A visual on a descending rocket is half the battle. The more money one puts into a rocket, at least I find it reassuring if I know where it's at while it is out of sight.
    I put a Wildman Jr. up 6k and never see it again until I walk up to it with the APRS tracker. I see on the Garmin that live tracks the rocket, the last known position and go towards it. As I get closer, I open the squelch on the radio and if I hear the faint "brrrrrrppppp" of the Beeline 70cm GPS tracker, even though the rig can't decode it, I know I will find the rocket. As the signal gets stronger the final position will be had. Helpful if stuck in standing corn.
     
  18. Mar 13, 2019 #18

    Earache

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    LDRS last May. Eggfinder Mini in a Madcow 1.6" fiberglass DX3. The first shot is the parachute on top of the wheat with the rest of the rocket hidden deep. I couldn't see the parachute until I was about 10 feet away. The other shot is the trail I blazed to get to the rocket. I had no visual of the rocket on the way down. IMG_0387.jpg IMG_0388.jpg
     
  19. Mar 13, 2019 #19

    Eric Jimenez

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    Oh I see now. I use two GPS coordinates. One for my location and the other one for the rocket. With that I can find the bearing of the rocket every second or so and display it on the screen with an arrow. At least for the moment I can just take out a compass and follow the arrow or plug in the coordinates to google maps. If I lose signal, the last GPS coordinates are saved. I think that fixes most of the problem in case the rocket is out of sight. Of course these devices are an aid and visual confirmation is always a plus.
     
  20. Mar 14, 2019 #20

    jbr

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    trails like these are what gets us banned from sites
    you have destroyed some of the farmer's profit
     
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  21. Mar 14, 2019 #21

    Steve Shannon

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    If the farmer in this case were not involved your criticism might be reasonable, but in this case Maddox Farms is extremely supportive. They were fully on board with the activities and in fact they worked hard to provide a large flat beautifully prepared launch site. Tripoli Central California has developed an excellent rapport with the family. The family attended the launch, the banquet, and the live band and they were very vocal to me in their support for rocketry.
    Also, this wheat field was furrowless; there was no way to get in to retrieve a rocket without leaving a trail of some kind.
     
  22. Mar 14, 2019 #22

    jbr

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    very good, I was aghast being a farmer in a past venture myself, it is all good if the farmer condones it
    there are ways to go thru wheat fields that leave little damage, I traveled thru many of mine looking for pest problems
     
  23. Mar 14, 2019 #23

    jbr

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    I owned 160 acres, was in a partnership that farmed 1000 more, mostly wheat, some cow chow
    waiver on the property was limited to 5000 feet
     
  24. Mar 14, 2019 #24

    Steve Shannon

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    I worked for a wheat farm in 1973, right after graduating from high school. We would always walk between the rows if we had to enter a field in order to minimize loss. In this case the wheat was planted without rows, very densely. I haven’t followed wheat farming techniques but I’d never seen this done before. I don’t know how a person could enter one of these fields without damaging some plants. Of course as you correctly pointed out we should always try to leave our launch sites better than they were when we arrive and that also includes minimizing the cost to our landowners.
     
  25. Mar 14, 2019 #25

    cerving

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    Maybe they plant them without rows figuring that whatever wheat they may lose by entering the field will be offset by the increase in crop density. In theory, they shouldn't really have to enter the field once it's planted... spraying can be done overhead. This assumes that they get enough rain so that they don't have to irrigate the field... that sure hasn't been a problem this year.
     
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  26. Mar 18, 2019 #26

    midpower_madness

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    I have plans already. PM me and I'll share my knowledge with you. I currently work with LoRa 30dbm module + authentic Ublox neo m8n. Uses UBlox demo software for a serial connection @ 9600 bps. Total price..... drum roll........ $75 USD for a complete system. I have had 20 km range with this unit. Sure it could do better.
     
  27. Mar 18, 2019 #27

    Eric Jimenez

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    Will do! I'm also using LoRa but not quite completey familiar with it. Any extra info is always helpful.
     
  28. Mar 18, 2019 #28

    BLH

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    Low cost is good. Remember to comply with FCC part 95 and make a legal unit, max transmission time at any frequency in 915Mhz band is 0.400 seconds in any 20 second time frame. At 9600 baud, this means one can only send 400 bytes every 20 seconds using FSK or OOK modulation. It is really tricky to do with LORA because of its slow transition data rate (symbol rate) and only a few bytes can be transmitted at a time... When I was playing with LORA radios, a maximum of 10 bytes could be sent out at a rate of every 5 seconds to comply... Does depend of spreading and BW setting...
     
  29. Mar 19, 2019 #29

    midpower_madness

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    Haven’t seen any rules specific to this in Canada - I do know EByte is FCC approved. We are allowed up 7watt transmitters on 902- 935 mhz spectrum. Did ask about GPS/ GNSS beacons and got the go ahead to build these devices for school here. Right now I operate at 1-5 pulses per second with a
    spreading factor of 502 khz. Power output on the modules is 700-1000 mW at 2.4 Kbps.
     
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  30. Mar 19, 2019 #30

    BLH

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    Wow, in Canada it appears one could use large spectrums and bigger RF power. That's cool! I think here in US the limit is 1W and probably why 30dbm modules are available up there, and here. Nonetheless, I am certainly no expert on radios and regulations, but what I can say about this topic is,

    "1-5 pulse per second" Not sure what that means but if its GPS data packets per second, that's really fast if all one wants is GPS location... How fast can a rocket drift? Depends on the application I guess. If its acceleration data for example, that might be a little slow... Use sim Card is a better idea.

    I think the 502KHz is good as that seems to make it 0.4 seconds of TX time per 10 seconds per part 15 because its above 500.

    As for 30dbm, I have had links work over 100 miles with that much power. That's like allot eh! Do you fly rockets up there that require that kind of range? I may come. What's the celling you have?

    I usually set my HPR rocket ISM band TX power around 16dbm to get around 10 miles range. In amateur radio, remember to be polite and don't blast large amounts of data out at max power for no reason... Lower power is hugely advantageous to battery life also as RF amps have notoriously low efficiency and suck your batteries dry fast. And their heavy...

    It seems in the 915MHz ISM band, the two things they don't like for obvious reasons are,

    1) Spurious harmonic emissions from impedance mismatches, nonlinear amp drive(Higher Power Harmonics), etc. that cause interference in other bands.

    AND

    2) Devices that transmit on one frequency for extended times and "Jam" the channel.

    Frequency hoping is the desirable link architecture for the ISM band.

    On 2400baud, that will give improved signal to noise as slower is better for data errors... Awfully slow though. I'll bet at 500KHz spread, 4800 will work for great distance. If my math is right, every doubling of the BAUD rate will half the Tx time. With LORA I'll bet 14400 is even doable. Now that will make your batteries smile!

    There are so many possible configurations, who knows... Happy tracking!
     

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