Eggtimer Rocketry
Tips and Tricks


What does the Eggtimer TRS do?

The Eggtimer TRS (just "TRS" from now on...) is a two-channel deployment controller with a built-in GPS/RF tracker.  Besides deploying Drogue and Main parachutes, it also sends out NMEA-formatted GPS positional data, which you can use to easily find your rocket's landing spot.  Because it has a wireless connection built-in, you can program the deployment settings, check your TRS' status, arm it for flight, and perform other functions wirelessly.

How much does it cost?

The kit is $90, plus shipping.   You'll need a receiver to go along with it, either the Eggfinder RX "dongle" or the Eggfinder LCD handheld receiver will work.

So I have to put it together...

Yes, like other Eggtimer Rocketry products it is a kit... you have to solder it together.  We won't lie to you, this is not a kit for beginners, but if you have a reasonable amount of electronics experience it won't be too difficult.  There ARE a lot of small surface-mount parts, so you WILL need a lighted magnifier (either a desk-mount "ring" magnifier or a lighted "head" magnifier) to build it.

Can I get one already built for me?

Nope.  We don't sell pre-built kits for a number of reasons, the primary one being that we just don't have the resources.  We also believe that it's a good idea if you are dealing with rocketry electronics that you understand how it works... besides, these are skills that you are probably going to need sooner or later anyway.

What's the difference in functionality between the TRS and the Eggtimer?

The TRS is designed to be a total recovery system (and thus the "TRS" name), for deploying parachutes and telling you where your rocket landed.  It has the two basic pyro channel functions (Drogue and Main), and streams NMEA-formatted GPS data to your receiver.  For most rockets, that's all you need in terms of electronics.

The Eggtimer TRS is based on the "classic" Eggtimer, but the functionality has been skinnied down to allow us to fit the GPS/RF interface into the firmware memory space.  The "classic" Eggtimer also has two pyro channels, but they can be configured much more flexibly than the TRS.  For example, you can configure the "B" channel to be used for airstart motor ignition or to fire after a configurable delay from launch; you can't do that with the TRS.  The Eggtimer also has three logic-level outputs which can be buffered through an Eggtimer AUX driver board to provide up to three  additional channels.  What it can't do that the TRS can do is to send out GPS data and be programmed remotely (although you can send out time/altitude data from the serial port and connect it to a separate transmitter (not included, obviously).

What do I need the USB-Serial cable for?

Most of the common functions (setting Drogue mode, Main deployment altitude, testing the channels, arming for flight, etc.) can be programmed remotely through an Eggfinder LCD receiver.  However, functions that require a lot of data movement (downloading flight detail, flash updates, etc.) can only be done through the USB-serial cable.  Also, you need the cable to program the frequency and ID code, and give the Eggtimer TRS a Device Name; you'd lose the connection to a remote unit if you changed the frequency over the radio, and there's no keyboard on the Eggfinder LCD to enter the text for a name.

Can I use an Eggtimer TRS with my Eggfinder RX "dongle" receiver?

Although we strongly recommend using the LCD receiver, you CAN use the RX "dongle" receiver... with some limitations.  You need to program your TRS to the same frequency as the RX, and you need to set the ID code to zero.  The data stream that you get will look almost exactly like an Eggfinder TX, except for a few extra non-NMEA records that are used to send the altitude and channel status data during flight.   The exact same functionality applies... you'll typically use some software like MapSphere to track your rocket, or connect an HC-06 Bluetooth transceiver to it to send the data to an Android device running some kind of GPS tracking software such as Rocket Locator.   You can't use an Eggfinder RX receiver to program your TRS, however; it has no provision for sending data.

Are there any special mounting requirements for an Eggtimer TRS?

One... you need to keep the antenna away from large masses of metal.  That means that you can't put it in an AV bay with two allthreads running through it, without the range being seriously compromised.  We like to put them in the nose cone when we can, but if you have to put it in an AV bay with allthreads we recommend that you get the RP-SMA antenna connector and use an external "rubber duckie" antenna, located outside the AV bay connected by a short coax cable.  Loop the cable once and zip-tie it to the shock cord, and wrap the antenna around the shock cord with some duct tape, and you'll be fine.  You could also get a longer RP-SMA bulkhead connector and screw it to the AV bay bulkhead, and attach the antenna directly.

What kind of battery does it take?

We recommend 2S 7.4V LiPo batteries, 500 mah or larger, for the computer/GPS side.  For the deployment side, whatever battery will fire your igniter is fine.  Having a separate battery for the deployment side absolutely prevents any chance of a battery problem or igniter short from affecting the computer/GPS side; this is the same philosophy that is behind the "classic" Eggtimer.

If you are using very low-current ematches you can use a single battery for both the computer/GPS and the deployment side; just make sure that the battery can source 10x the all-fire current of your igniter.  Most LiPo's are rated at least 20C nowadays, so just about any one rated 500 mah is going to be able to handle it no problem.

How big is it?

It's about 3.9" long and 1.3" wide, it will fit in a BT55 body tube or a 38mm coupler.  The wire antenna adds about 3.2" to the length; if you are using an RP-SMA connector instead, that only adds about .5" + whatever your cable connector takes.

What is the Range?

We've tracked rockets to over 5 miles, only losing the signal when it dropped behind a hill.   We drove to the back side of the hill to retrieve it... and it was pretty much right where the last packet said it was.

Do I need to get a special license to use it?

Nope, the Eggtimer TRS uses the 900 MHz license-free band, just like the Eggfinder transmitters.  Outside the US and Canada, we have region-specific versions for the UK/EU, and Australia/NZ that are customized to their specific regulations.

How high will the altimeter go?

The barometric pressure sensor in the Eggtimer TRS is rated to about 70,000', but the software will basically go as high as you can until the sensor stops responding.  We recommend a ceiling of about 60,000'... above that you'll need some other deployment mechanism anyway, because the thin air doesn't work well with deployment charges.