Eggtimer Rocketry
Tips and Tricks

Eggfinder FAQs

How does the Eggfinder work?

The Eggfinder GPS Tracking System consists of two boards:  A transmitter module that goes into your rocket and a receiver board that is connected to your laptop, tablet, or smartphone.  The transmitter module contains a GPS module that tracks the latitude and longitude of your rocket as it moves, and that data is transmitted to the receiver module on the ground.  Using readily available (and mostly free!) software on your laptop, tablet and/or phone, you can take the received data stream and create a real-time track of your rocket's movements, and most importantly locate its landing spot so you can easily find it.

How much does it cost?

The Eggfinder Starter Set, consisting of both the TX transmitter and RX receiver "dongle" modules, is $90 for the kit.  The Eggfinder LCD Starter Set, with the Eggfinder TX module and the Eggfinder LCD display reciever kits is $120.  An extra TX transmitter kit is $70, an extra RX receiver kit is $25, and the Eggfinder LCD receiver kit alone is $55 (you save $5 by purchasing both a transmitter and receiver together).   

We also have a smaller version of the transmitter, the Eggfinder Mini.  It's $5 more than the "standard" Eggfinder TX transmitter, but it's a lot smaller... only .7" wide and 3 1/2" long with the (included!) external antenna.  It's perfect for those minimum-diameter projects or for being wrapped up in a chute protector and taped to your shock cord (like you might do with a RDF tracker).

What is the range?

We have tested the Eggfinder to nearly 10,000' triangulated (altitude and downrange) with the included "wire" antenna.  If you use a half-wave "rubber duckie" antenna on the receiver (under $20), you can double that range, at least.  We've tracked rockets to over 5 miles with that combination. 
  Due to a number of factors not necessarily related to the hardware, you may lose contact for a few seconds as your rocket goes through boost, however as it slows down near apogee it will be reacquired and you will be able to track it almost all of the way coming down, which is the real goal of having a tracker in the first place.  

How close will it tell me to where my rocket actually landed?

The GPS module is rated to a typical resolution of 2.5 meters.  In reality, you will probably lose your radio signal when the rocket gets very close to the ground, but the last latitude-longitude figure will be very close.   In testing, it's been within a few feet.  Unless you land in a tall grassy area, you will almost certainly see your rocket laying on the ground well before you near the last reported GPS position.  Once you get close to the rocket, even if you can't see it, you'll pick up the updated location and be able to walk right up to it.

Do I need a special license to use an Eggfinder?

The Hope RF radio module used in the Eggfinder runs on the 900 MHz ISM band, which does not require a license in the US.   Like other FCC Part 15 devices, the rule is that it must not cause interference to other licensed-band devices; since it is a low-power device and is intended to be used in a remote location rather than in a home/office environment, it is extremely unlikely to cause any interference to anything at all.

We also make versions for other regions, such as the EU/UK and Australia/NZ, which comply with their specific license-free requirements.

What software can I use to show me where my rocket landed?

We've used a number of software programs on the laptop, inclduding Hyperterminal just to capture the NMEA serial data stream.  MapSphere is a nice freebie software that can show you your rocket's track in real-time, it runs on Windows. We've also used some programs on Android phones/tablets that work well, Rocket Locator is one that's specifically designed for finding rockets, and Polaris Navigation is a more generic app that we like too.  For iOS, we've used MotionX.  With iOS you'll have to manually plug the coordinates into your app, since iOS generally doesn't support external GPS connections.

The general procedure is to capture the NMEA data until it stops streaming, which means that your rocket has landed (although if it's close enough you still might pick it up on the ground as well).  You take the last recorded latitude and longitude and set a waypoint in your GPS-enabled phone/tablet's app, and tell it to navigate to that waypoint.  With your handheld device, you simply walk up to that waypoint, and your rocket will be right there.

How does the Eggfinder compare to other GPS radio systems?

The Eggfinder is a little different in that it is a very simple system, its sole purpose is to send the NMEA-formatted GPS data to your laptop/tablet to tell you where your rocket is.  There are some other much more expensive systems that have the GPS system integrated with a flight computer, or that use a licensed band such as 70cm to provide more transmitter power and greater range, but for the majority of hobby rocketry sport flyers the Eggfinder is adequate for the vast majority of the flights that you would ever attempt, and it is much more affordable.

How hard is it to put together?

We're not going to lie, it's not a good first soldering project, but if you have built other reasonably complex kits with ICs on them (such as an Eggtimer) you shouldn't have too much trouble with it.  There are surface mount parts, but they are relatively large by SMT standards; none of them are under .050" pitch.  To make things easier on you, we include some .020" low-temperature no-clean solder with the kits, this makes soldering the GPS module really easy compared to trying to use the stuff that you get at Radio Shack.

Are there any special mounting requirements in my rocket?

One cardinal rule:  Keep the antenna away from anything conductive!  That means that you can't put the Eggfinder inside the AV bay with your altimeter and two allthreads running next to the antenna and expect to get a good signal.  We recommend that you mount the Eggfinder in the nose cone of your rocket with the antenna pointing upward.  Note that carbon fiber blocks radio signals, so you will need to come up with an external antenna if you have a CF rocket.

What kind of antenna does it use?

The standard included antenna is a very simple 1/4 wave "whip" (about 3" long), it is simply soldered onto the board right next to the RF module.  With this antenna we've achieved over 10,000' triangulated range, we feel that it will be adequte for the vast majority of sport flights.  If you need more range or if you need to mount the antenna separately (i.e. you have a CF body tube), you can optionally solder a RP-SMA connector to the board instead of the whip.  There are a number of 900 MHz RP-SMA antennae available, Google them or look on eBay.  You'll need an omnidirectional antenna on the rocket, but if you use a wide-beamwidth panel antenna on the receiver (10 dB gain, around 60 degrees beamwidth) you should get almost twice the range, at the expense of having to point it at the approximate location of the rocket to get a good signal.  With 3 dB omnidirectional "rubber duckie" antennas on both ends, it's been flown to over 25,000' without losing the signal.

The Eggfinder Mini comes with a 2.4 dB gain screw-mount antenna, you should expect similar range out of it compared to the "standard" Eggfinder TX tramsmitter.

What kind of battery does the transmitter require?

We recommend using a 7.4V ("2S") LiPo battery, at least 300 mAH.  You CAN use a smaller one, the Eggfinder TX draws about 70-100 mA when it's running, but that will reduce your operational time, of course.  If you want to use a smaller battery we recommend that you power it up shortly before launch... mounting it in the nose cone or wrapped up in the body tube. usually makes that pretty easy to do. 

What do I need if I want to connect the receiver to my device with Bluetooth?

You'll need to add a Bluetooth-Serial module and a battery.  We recommend using a "HC-06" Bluetooth module, look them up on eBay; they're under $10.  You don't need to reprogram them, they are compatible with the Eggfinder receiver out of the box.  For a receiver battery with Bluetooth, you can use 4 AA batteries in a holder or a 2S 7.4V LiPo, at least 1000 mAH.  Bluetooth draws a lot of power, and you want the receiver to be able to run all day on a charge or set of batteries.  You'll also most likely want to put this is some kind of case, Radio Shack sells some decent plastic ones for around $5 that work well.  If you choose the LCD receiver rather than the RX "dongle" receiver, you get a battery box and case, so all you need is the HC-06 module.  This setup works really well if you have an Android phone/tablet, using Rocket Locator to point the way to your rocket.

The advantage of this solution vs. the USB-Serial cable is that it's easier to take with you as you walk out to your rocket, and you can use the blinking receive-data LED as an indicator that you're getting close.  It's also very handy if your tracker separates from your rocket and you need to go looking for it... yes, we know that from experience!

Can I fly more than one Eggfinder at a time?

Yes, but you'll have to make sure they're on different frequencies.
There are nine base frequencies from 909-925 MHz in 2 MHz increments, and eight ID codes, so you can have up to 72 Eggfinders operating simultaneously.  The TX transmitter (Rev B6 and above) and the LCD receiver can be "paired" up so that the are programmed together to the same frequency, using a simple 3-conductor jumper cable.  The RX "dongle" receiver uses a fixed frequency, so it's not programmable; you'll have to make sure your TX transmitter matches its frequency if you're using one of those.

What is the difference between the Eggfinder RX and Eggfinder LCD receivers?

The Eggfinder RX receiver is a "dongle" that has a USB cable that plugs into your laptop or tablet.  It is the equivalent to a "ground station".  You configure it on your device as a serial port, and the GPS data from your Eggfinder TX transmitter flows through that serial port.  Using any GPS-enabled software package on  your laptop/tablet (such as MapSphere on Windows), you can get a track of the rocket's path,  and more importantly the landing coordinates.  You can also turn the Eggfinder RX into a handheld receiver by substituting the USB cable for a battery and a HC-06 Bluetooth module, you'll probably want to add a case too.  If you do this, you can carry the Eggfinder RX and your device with you as you approach the rocket, so if the coordinates have changed because the wind dragged it along the ground (or a well-meaning fellow rocketeer picked it up and drove it back to the pad) you'll know right away.

The Eggfinder LCD receiver is a portable receiver with a LCD display that shows you the latitude/longitude in real-time, along with a few other tidbits of useful information (see the Products section).  It is designed to be used with a smartphone or portable tablet.  You simply enter the coordinates into your smartphone's navigation app, and walk right up to your rocket.  It also has a beeper that lets you know when you have a fix, this is very useful for helping to locate your rocket in the event that it goes out of range.  You can configure the displayed coordinates' format to match your app.  You can also set it to any Eggfinder TX frequency, so the same Eggfinder LCD receiver can work with any number of Eggfinder TX transmitters.  Like the Eggfinder RX, you can also add a HC-06 Bluetooth module, so if you have a Bluetooth-GPS enabled app on your Android or Windows tablet/phone you can get real-time tracks. Finally, you can use the LCD receiver to program the frequency on your TX transmitter (Rev B6 and above), you can''t do that with the RX dongle.

I live outside the USA, can you sell it to me?

Currently, we can ship to the USA, Canada (with some restrictions, email us...), Australia, and New Zealand, subject to some frequency selection limitations (i.e. Australia ships from 919-925 MHz since the lower frequencies are allocated for other purposes).  In the EU/UK, we can ship on 869 MHz; email us for details.  Shipping will be higher, of course... contact us for details.

What?  ANOTHER silly name?

Yup.  We couldn't resist... after all, you got an Eggtimer to control deployment on your rocket, so it seemed natural that something that would help you get it back would be an "Eggfinder"...