The Eggfinder - A Low-Cost GPS/RF Tracking System

Yes, several times. I've tested it to over 8,000' range (altitude + downrange, triangulated) with good RF signal and GPS data. You WILL lose it on boost, of course, but it gets picked up a few seconds later in the ascent, and you get data pretty much the whole time during descent until it gets low enough to the ground that you don't have clear line of sight anymore. Typically that's under 100' altitude which is going to be within a few seconds of landing, so your last reading should take you right to your rocket.

mikec said:

Have you flown the GPS module you're planning to use? I see on your web site that you want to use a SIRFstarIV-based system. Older SIRF units are notoriously bad for not working in rockets. Just FYI.

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cerving said:

Yes, several times. I've tested it to over 8,000' range (altitude + downrange, triangulated) with good RF signal and GPS data. You WILL lose it on boost, of course, but it gets picked up a few seconds later in the ascent, and you get data pretty much the whole time during descent until it gets low enough to the ground that you don't have clear line of sight anymore. Typically that's under 100' altitude which is going to be within a few seconds of landing, so your last reading should take you right to your rocket.

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So you need to have the computer running / recording before flight to capture in air signals? I was hoping it could use it as needed (only if it looks like a tough recovery or you lost your reference).

Just wondering, can you import a graph of the flight into google earth or something like that?

It's like the kids in the back seat on a road trip , are we there yet . But now it's is it ready yet

I'm just getting into HPR, I have my eggtimer built and mounted in my Darkstar Jr. Haven't flown it yet, but I'm scared of losing my first HP rocket that I've put so much time and effort into. With a tracker like this I would be confident to get my L2 cert with the Darkstar Jr. on a J motor and not worry about losing it. I built the nosecone with a removable bulkhead just for something like this in the future. Plus, with a baby on the way my budget will be dwindling quite a bit and this will still be attainable! That’s an exciting prospect!

Is the 900Mhz module and antenna you are using already FCC pre-certified? If not then only HAMs will be able to use this correct?

Good question. Hope RF tests their modules and publishes the test results, to show that they are compliant with the FCC's spectral regulations. They do not formally certify them, however, leaving that up to the system integrator. The FCC exempts hobbyist kits from certification by policy, I have it it writing from their Chief of Spectrum Enforcement. They're not interested in picking on hobbyists, especially in regards to low-power Part 15 use; if they were then you wouldn't see any kits at all. I have yet to find ANY kit that's FCC certified, from ANYBODY. The 3DR radios aren't certified either, and you can hardly call them kits, especially the newer ones that come in a plastic case rather than being a bare PC board.

FCC certification would be required if I was producing a FINISHED product. There was at least one guy that got in trouble selling assembled radio transmitter kits over the Internet that he bought directly from a kit manufacturer. He wasn't doing to make money really, but another radio manufacturer complained so the FCC was obligated to call him out. They would rather have left him alone, but they had not choice since he was "marketing" it. They lightly slapped the kit builder's wrist and didn't even contact the manufacturer of the kit. From what I have seen, he's still assembling these kits, but he's having the end user purchase them and send them to him so he's doing it as an assembly service which takes him out of the regulatory loop.

BTW, any telemetry product that's being used under a Ham license requires some mechanism of sending out your call sign periodically. The Eggfinder isn't smart enough to do this, it simply streams out NMEA GPS data. Units (such as those produced by Altus Metrum) that are designed to be used on the licensed 70cm band DO send out call signs, and are generally somewhat more capable and expensive than the Eggfinder.

jderimig said:

Is the 900Mhz module and antenna you are using already FCC pre-certified? If not then only HAMs will be able to use this correct?

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mikec said:

Have you flown the GPS module you're planning to use? I see on your web site that you want to use a SIRFstarIV-based system. Older SIRF units are notoriously bad for not working in rockets. Just FYI.

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This has been my experience with sirfstar 4 parts as well. I was extremely disappointing with the performance, even under ideal conditions (big patch antenna with clear view of sky).

Other than that it looks like a nice solution. Great work!

Yes, but that's true of just about any RF-GPS solution. Once they're on the ground, the radio's range decreases dramatically and it will be harder to pick up the GPS feed. You want to get it while it's still in the air.

Beacon-type radios (like the Walston, for example) require that you move in the general direction of where you think it may have landed, using some kind of directional receiver antenna (typically a Yagi), and progressively home in on the rocket as you see the signal strength increase. It requires practice and patience. With a GPS, you get the data in the air before it lands, so you're ahead of the game. You might not necessarily get the exact landing location, but it's going to be very close. The tradeoff is that you have to do a little work ahead of time, i.e. turn on your laptop/tablet and start some kind of recording/tracking program.

cavecentral said:

So you need to have the computer running / recording before flight to capture in air signals? I was hoping it could use it as needed (only if it looks like a tough recovery or you lost your reference).

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cerving said:

The FCC exempts hobbyist kits from certification by policy, I have it it writing from their Chief of Spectrum Enforcement.

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That is very interesting and useful. Thank you.

Do you know what defines a 'kit' as far as the FCC is concerned? Does solder have to be involved or can simple assembly connections qualify. This could open up all sorts of license free RF possibilities......

Edit. Would you share the contact info for the Chief of Spectrum Enforcement here or a PM so I can get that in writing also?

The FCC definition of a kit (from Part 15.3(p)) is:

(p) Kit. Any number of electronic parts, usually provided with a schematic diagram or printed circuit board, which, when assembled in accordance with instructions, results in a device subject to the regulations in this part, even if additional parts of any type are required to complete assembly.

There have been some rulings that simply plugging ICs into sockets and/or mounting an assemble board into a cabinet does not constitute a kit. The assumption is that some level of electronics expertise is required to construct a kit. That makes sense to me. I guarantee you that when you see the bag of parts in the Eggfinder, you will know that it is truly a kit by anybody's definition. It will be a little more challenging than an Eggtimer, but I'm including some very fine low-temperature solder to make mounting the GPS module and the MCU easier.

The FCC reference is from the aforementioned enforcement action, the opinion was written by John Poutasse who was and still is the Cheif of the Spectrum Enforcement Division. Contained within it, and I quote:

Section 302(b) of the Act provides that "[n]o person shall
manufacture, import, sell, offer for sale, or ship devices or home
electronic equipment and systems, or use devices, which fail to comply
with regulations promulgated pursuant to this section." Under Section
2.803(a) of the Rules, the Commission prohibits the marketing of radio
frequency devices in the United States unless the devices are
authorized under the appropriate equipment authorization procedure and
comply with the applicable technical standards as well as the
administrative requirements relating to equipment labeling and
consumer disclosure. Under Section 15.201(b) of the Rules, intentional
radiators, such as AM transmitters, must be certified in accordance
with the procedures set forth in Sections 2.1031 through 2.1060 of the
Rules. "Kits," as defined in Section 15.3(p) of the Rules, however,
generally do not require authorization.

This pretty much lays it out... if you produce a KIT, you do NOT need to go through the lengthy and expensive certification procedure. There is an exception for "TV interface devices"; it goes back to 1989. I think that's about the time that a lot of kit cable descramblers came out, and a lot of them were very poorly designed. An engineer friend of mine got one, it barely worked and it screwed up the other TVs in his house so he quit using it. My guess is that the FCC got a lot of complaints from neighbors and felt compelled to put a rule in place. Back then, there was virtually no satellite TV, and cable TV penetration was maybe 50%, so anything that leaked TV RF had a good chance of screwing up TV reception.

cerving said:

Yes, but that's true of just about any RF-GPS solution. Once they're on the ground, the radio's range decreases dramatically and it will be harder to pick up the GPS feed. You want to get it while it's still in the air.

Beacon-type radios (like the Walston, for example) require that you move in the general direction of where you think it may have landed, using some kind of directional receiver antenna (typically a Yagi), and progressively home in on the rocket as you see the signal strength increase. It requires practice and patience. With a GPS, you get the data in the air before it lands, so you're ahead of the game. You might not necessarily get the exact landing location, but it's going to be very close. The tradeoff is that you have to do a little work ahead of time, i.e. turn on your laptop/tablet and start some kind of recording/tracking program.

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Figured that was the case and pretty much the same with anything else. Need to clean up a semi disposable laptop for field use.

You can also hook the receiver up to a Bluetooth(R) module and use it with an Android tablet. I've used it with a Nexus 7, works fine.

cerving said:

You can also hook the receiver up to a Bluetooth(R) module and use it with an Android tablet. I've used it with a Nexus 7, works fine.

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My Samsung Galaxy 2 has blue tooth. That could work.

cavecentral said:

Need to clean up a semi disposable laptop for field use.

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For my homebrew tracking system, I built a simple handheld unit with an Arduino and a two-line LCD screen that displays information about the rocket's position (lat/lon, altitude, bearing and range from initial position, and number of satellites), and I use a handheld Garmin GPS to find it after landing. I like that better than having to carry a computer or even a tablet around.

mikec said:

For my homebrew tracking system, I built a simple handheld unit with an Arduino and a two-line LCD screen that displays information about the rocket's position (lat/lon, altitude, bearing and range from initial position, and number of satellites), and I use a handheld Garmin GPS to find it after landing. I like that better than having to carry a computer or even a tablet around.

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I had an Arduino some 900Mhz XBees and a GPS module to try to build my own tracker. Realized this wasn't my thing (electronics) and gave them to a club member that had much greater success with such things.

When this comes out, what are the odds that you'll sell an Eggtimer + Eggfinder combo at a discount?

:wink:

Zeroignite said:

When this comes out, what are the odds that you'll sell an Eggtimer + Eggfinder combo at a discount?

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And now I looked at the Eggtimer documentation more closely, I see it has a live-data serial feed. I smell live telemetry coming, and really hope I'm right.

A cheap mapping solution for the EggFinder would be MapSphere: https://www.mapsphere.com/ . Get the addin so you can download different maps and aerial photos. The google aerial maps don't work anymore but the others are adequate enough. The key with this program is you can download the desired maps before you go to a launch so your maps are portable. Won't work in Linux with WINE because the software uses some sort of screwy port detection. Will work in an XP client with Vbox on a Linux machine though. The EggFinder receiver proabably behaves like a USB GPS receiver hence one can remotely track a rocket. The only problem is I haven't figured out how to get the lat/long displayed on a screen. One can easily save the track to a file and open it though for reading and manually transfering position to a handheld GPS if one doesn't want to drag a laptop out to the recovery site.
This would be the cheapest graphical receiving station I can think of. The software and maps are free and portable. You still can dig up your final lat/long and input it into a handheld GPS to take you to the rocket or if you have a small tablet that will run the program you can carry it along. MapSphere will not recognize more than one GPS input. Darn, but heck it's free.
Remember laptop screens are hard to see in the sun so be prepared to sit in the vehicle for a look or throw a blanket over your head!:kill:
Oh, if one has a USB GPS receiver on hand, you can download MapSphere now and work with before you even get an EF. You'll be tuned up and ready to use it when you get it built.

Let me mention there is no "perfect for everyone" APRS tracking program out there. There are trade offs for each one. MapSphere with an EggFinder would be a very economical solution
that doesnt' require a Ham license either! Kurt ( I want two)

I just want to say we had great success testing the Eggfinder this weekend and it should be released soon, I will let Cris fill you guys in more.

ksaves2, I have been using MapSphere and it works well. In fact, there is a tutorial on using it in the Eggfinder User's Guide (which I haven't posted quite yet). As you have mentioned, it does have a few annoyances, the chief ones being that it doesn't display the coordinates when you mouse over a location, and it doesn't save the track as an NMEA-formatted file. Still, it's easy enough to get the last coordinates from it, which is what you're really looking for, and if it doesn't have a map loaded it will still show you the track.

As jus_rockets mentioned, I drove up to Eagle Eye to fly with TRAPHX yesterday, and it was definitely worth the drive. (If you ever get a chance to go up there, give it a try... they got some nice people there. Be sure you have a tracker though, their range is about 100 square miles of scrub brush.) Both flight tests went perfectly, we literally walked up to the rocket on the first flight, and we were able to find the lost Eggfinder on the second flight when it separated from the shock cord. (Hint: don't use electrical tape to attach a tracker to a shock cord.) I'd like to give a public Thank You to the people at TRAPHX for being so accommodating. :clap:

Now that the testing is pretty much complete, I just need to polish up the documentation and finish getting them kitted. It should be about a month.

That's,good ,just to bad it will not be ready for me to test at thunder struck in april .

I'm really looking forward to this . count me in when kits are ready

PCB's and other parts are on order, and I have updated the Eggtimer Rocketry web site with the assembly docs and pictures (www.eggtimerrocketry.com). Should be about two weeks.

Is there a set price yet? Will a kit include a tx and rx?


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Ok, so the Eggfinder /won't/ work on a 1-cell 3.7v lithium? What's the mass of the 3" antenna? Is there an established max range, or is 8,000ft LOS the farthest you've tested to? How about timer + finder kit pricing?

The Eggfinder Starter Set with a transmitter kit and a receiver kit will be $90 + $5 s/h. Extra transmitters will be $70, extra receivers will be $25. I'll also have RP-SMA edge connectors available for $3 each if you want to use an external antenna instead of the included whip. There's plenty of people selling 900 MHz antennas, so I'm not going there.

It runs on 3.3V, that's a little too low for a 1S LiPo with a regulator. That's why I recommend a 2S. I'm specifying a 4.5V minimum.

The standard whip antenna weighs just about nothing, it's simply a piece of 1/32" wire that you solder to the board. If you add the RP-SMA connector and your own antenna, that will weigh more, obviously; I've tested some dipoles that are maybe about 7" long with the connector, they probably weigh about an ounce.

I have not been able to fly it far enough to get the maximum range, but I have a beta tester who will be doing that. I do know for sure that it's good to around 10,000' line-of-sight. You don't necessarily need the signal at apogee, you need it coming down, since the goal is to get the last GPS coordinates where your rocket landed. Typically, I get signal until right before it lands; ground range is obviously not as good as open-air range.

I haven't decided on what I might do about a combo yet, but there's a good chance that I'll do something.

Zeroignite said:

Ok, so the Eggfinder /won't/ work on a 1-cell 3.7v lithium? What's the mass of the 3" antenna? Is there an established max range, or is 8,000ft LOS the farthest you've tested to? How about timer + finder kit pricing?

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