Author Topic: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter  (Read 1429 times)

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Offline fuzzoli

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[Update:  Added link to the corresponding thread in Ye Olde Rocket Forum]

New Year, New Project...

Back in the 1970s, the model rocket company, Estes Industries, had a 27MHz transmitter that you would put into your rocket and collect telemetry on your CB Radio or Walkie-Talkie.  You could configure the transmitter for pulses (Rocket Finder Mode), audio, temperature, and spin rate.  It was a neat little transmitter.

I had the basic model back in the day.  Over the course of many years and moves, I've managed to misplace everything except the main owner's manual.

Obviously we can do far better using modern technology, but I thought it would be cool to build one from scratch.   So....

The goals of this project are:
  • Recreate the physical Transroc as close to the original as possible.
  • Use identical parts as much as possible.
  • Document the technical progress here on the EEVblog, with rocketry-related updates on Ye Olde Rocket Forum.com in this thread.
  • GitHub repo for all project files (photos, KiCad project, etc.)
  • Have some fun, and maybe learn something along the way.

-------

The main manual can be found here.  Additional links can be found at the end of this post.

Let's start with a 3D rendering of the finished transmitter:



The Transroc fits into the body tube of a model rocket, and transmits (typically) on CB Channel 14 (27.125MHz).  Let's dig in and start with the schematic:



The transmitter can be configured in one of several modes (mentioned above).  This version of the schematic is a combination of the Basic and Microphone kits.  Please note I've taken some liberties with the schematic.  In trying to keep the layout as close to the original as possible, while also matching up the PCB, some minor adjustments to the schematic had to be made. 



The board is single sided, and I assume it was originally laid out by hand.

Two versions of the board were ordered from JLCPCB.  The boards on the left are "modern", with a component silk screen, and a proper solder mask on both sides.   The second set of boards (shown on the right), are modeled after the original board.  The original didn't have any solder mask on the top layer, and the bottom mask covered just the copper.



This second format gave what I thought was a more realistic representation of the original board.  Here's part of the board from the manual:



It appears the solder mask covers only the copper, and not the space in between the "traces" (marked in green).

However, after the boards were ordered, Dave over on Ye Olde Rocket Forum was kind enough to photo his actual Transroc, and those photos seem to imply a solder mask covering the entire back side of the board. 



I've found some NOS for the transistors and PUJT, and I'll probably just replace the DZ805 diodes with 1N914's.  I also found
stock for Channel 11 and 14 crystals.  The biggest challenge will be the coils.  I pulled the sizes from the photos and found some slugs that match the dimensions.  For the coil forms, I've threaded plastic tubing.  The solution seems to be mechanically working, but I don't know how things will work in the real world.  I received samples of two different slugs from the kind folks over at Micrometals, so I'll be able to try each one to see which gives the best RF performance.  Unfortunately the threads are different for the two variations of the larger coil, so I'm going to build up the circuit on a breadboard first.

Next Steps

The next step is to epoxy the forms to the board and wind the coils; then build out the remainder on a breadboard.  I want to go this route as opposed to fully populating the board as I remember the Transroc being a very picky item.  Building out on a breadboard first may help tweak component values if need be.

Disclaimer:  I may need some forum help when it comes to the RF part of the circuit as I tend to think in ones and zeros and although only 27MHz, analog and RF aren't my strong points.

So stay tuned to this build log and hopefully a working transmitter will come to be! 

The Future

Not to get ahead of myself, but the intent is to build up this circuit more or less for fun.  Then, look a what's out there and see how many sensors and transmitters (think camera, WiFi, audio, GPS, etc.) I can fit into the same volume.  THAT should be a fun project!

Happy New Year to All!

-Frank

« Last Edit: February 25, 2021, 05:37:05 am by fuzzoli »
 
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Offline schmitt trigger

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #1 on: January 02, 2021, 04:17:56 am »
Although I cannot provide you with any technical tips you don’t already have, as a model rocket enthusiast I hope you are successful with your project.
Back in the 60s, with the space race going at full speed, model rocketry was extremely popular.
We never built a radio finder, but did build a xenon strobe.
 

Online Alex Eisenhut

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #2 on: January 02, 2021, 05:00:04 pm »
Wow I had the crappy Transroc II which was just a very loud piezo buzzer that attached to the parachute cords. No RF or anything like that.

You got a goofy-looking microphone and amplifier with headphones to help locate the rocket once it landed.

https://www.rocketryforum.com/threads/estes-e2-transroc-ii-transmitting-locator.40389/

*Except AC/DC adapters on eBay. Avoid them all!
 

Offline bd139

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #3 on: January 02, 2021, 05:03:46 pm »
Back when I was a kid we just lost our rockets  :-DD. Not sure the Transroc made it to the UK although I have to say that this is a very very very cool recreation. Thanks for posting it :)

The "original" boards look very authentic. I was trying to do some myself like that a while back, albeit I wanted transparent solder mask which JLC don't do :(
 

Online TheSteve

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #4 on: January 02, 2021, 06:22:28 pm »
Cool project! I had quite a few rockets back then, but never saw this option. I would have wanted it for sure.
VE7FM
 

Offline Conrad Hoffman

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #5 on: January 02, 2021, 09:06:59 pm »
I don't remember that product, but when I was a kid I built a few rockets and always wanted the "Camroc", that took single photos on a small disc of film- https://www.dembrudders.com/history-and-use-of-the-estes-astrocam-110.html

Never got one- hope you have fun with the transmitter!
 
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Offline bd139

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #6 on: January 02, 2021, 09:24:58 pm »
Ah yeah I had a later Astrocam. Must have been at some point in the mid 1980s. Flew it a few times, went to get it developed and it turned out nothing was exposed >:(. Never got to the bottom of it. Worst Christmas present ever
 

Online Alex Eisenhut

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #7 on: January 03, 2021, 02:02:37 am »
I got my Astrocam to work but the pictures were washed out. The plastic lens was not the greatest. Eventually I got a bad batch of C6-7 engines and the whole thing blew apart on the launch pad. Oh well.

Nice Transroc project BTW to the OP!
*Except AC/DC adapters on eBay. Avoid them all!
 

Offline JimRemington

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Offline fuzzoli

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #9 on: January 03, 2021, 02:54:26 am »
The current listing is only the Microphone Accessory kit, has been on eBay for a very long time, and is priced way too high for just an earphone, transistor and a few passives. 

A Microphone Kit and Spin Rate Kit recently sold on eBay for $52.21 and $38.52 respectively.

However, back in November, a mint Transroc base kit sold for $355.
 

Offline fuzzoli

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #10 on: January 03, 2021, 02:58:43 am »
Dan over at transroc.org is digging into his archives for the accessory manuals.  So far, he's posted PDFs of the Microphone and Spin Rate manuals.
 

Offline fuzzoli

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #11 on: February 06, 2021, 03:28:22 am »
I had to reorder the boards as after closer inspection, I noticed that the pads were a bit thin -- some almost non-existent.  As all pads were the same size, I'm not sure what happened -- perhaps I was hitting the limits of what the board house could do.  In any case, the boards look better now.

Now I'm on to figuring out the RF coils.  The Transroc has two coil sizes, and I received two slugs each from MicroMetals.  My question to my fellow EEVbloggers is which slug to choose?

For the Oscillator Coil,  I have TH35-0201 and TH35-0306F to choose from.  They are each of different materials and permeability.   This is for T1 in the schematic.  I'm not overly concerned during the design phase as both slugs have the same thread, I can easily change out one for the other to see which performs best.

The Antenna Coil (T2) is another story.  The slugs samples are TH48-0106F and TH48-2002.  Unfortunately, these slugs have different threads, so I'll have to end up tapping the coil form with the correct thread size for the final product.  For testing purposes, I plan to build out both forms and see which works better, but I was wondering if anyone might have insight into which of the TH48's might give the best results.

Note:  All of the possible slugs can be found at the bottom of this page on the MicroMetals site.

 

Offline fuzzoli

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #12 on: February 21, 2021, 09:35:46 pm »
Two updates for this week...

These photos show the coil forms and windings.  The forms were made from pieces of Evergreen Polystyrene Tubes (#227 and #229).

The rods were cut to size and tapped with the appropriate threads.  As mentioned above, the larger slug samples had different threads, so if this version fails to oscillate / perform, I'll try the other slug and tube.

The tubes were superglued into the bare board.  I was very happy with the milled holes JLCPCB did.  The tubes fit in perfectly, and the glue seems to be holding nicely.

Next came winding the coils.  Fortunately there are only a few dozen turns in total, so the windings came out pretty good.  As I don't have my original Transroc, I had to guess the wire gauge.  The gauge can be estimated by measuring the winding heights in the photos and then dividing by the number of turns.   The four measurements gave an average very close to 30 gauge, so that's what was settled on.   After soldering a "start" end to the board,  a sections was wound, and the windings secured with white glue.  The glue was set aside to dry before soldering the loose end to the board.  Continuity was verified and the assembly set aside for later.

 

Offline fuzzoli

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #13 on: February 21, 2021, 09:56:34 pm »
Next came the start of the breadboard build.  As the Transroc was known to be finicky, a breadboard version seemed prudent.

From the schematic, the first part to be breadboarded was the "Modulator Section".  This went together surprisingly well, and even worked the first time (how the heck did THAT happen!).   :phew:

The attached block diagram shows an expected pulse amplitude of 0.65v -- enough of a difference to modulate the transmitter on and off.  In this basic "Rocket Finder" mode, the telemetry is a simple pulsing of the transmitter.   Although the Transroc manual does not indicate any waveform timings, the scope screenshot shows a nice 131ms "on" and 502ms "off".  However, the amplitude of the pulse is only 503mV, which may not be enough to actually turn the RF on.  If that's the case, we'll have to play around with the resistor values to get it all working.  Perhaps this was the source of the original Transroc's pickiness.  Hmmm...

For reference, the screenshot shows the B+ voltage in Yellow (15v - one diode voltage drop).  The Green trace is the pulsing of the modulator section.

For reference, Spin Rate and Temperature modes replace R5 and C7 with appropriate values so as to drive the RF Section at a higher frequency.  The values are chosen to modulate the transmitter at audio frequencies.  This was tested on the breadboard by lowering C7 to something much smaller than 3.3uf.  The modulator was verified to oscillate at around 500Hz.

Next up will be to breadboard the RF section.  Pigtails will be added to the proper pads to make adding the coils into the circuit easier.
« Last Edit: February 21, 2021, 09:59:59 pm by fuzzoli »
 

Offline james_s

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #14 on: February 21, 2021, 10:34:05 pm »
There's something I find really appealing about recreating vintage products. Several years ago I made a handful of replicas of the computer interface Bill Cheek developed for several of the higher end Radio Shack scanners back in the 90s.

I built several model rockets when I was a kid. My favorite was a 2-stage one that I lost after it went up into the clouds. After that I built a model of a missile which was the straightest flying model rocket I ever built, unfortunately it landed about 50' up in a tree at my grandmother's place. Another landed in the drainage pond near the house where I grew up. They were fun but I remember the engines being quite expensive and it was always hard to find a space large and open enough to have a good chance of recovering the rocket.
 

Offline fuzzoli

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #15 on: March 05, 2021, 04:55:15 am »
...just a quick update...

The RF section is working after a bit of breadboard user error (I had the crystal off by one row).  |O  The modulator is properly pulsing the transmitter on and off per my previous post.

The one thing I'm troubleshooting now is the power output.  It's REALLY low -- total current consumption peaks at about 0.5 mA, which puts the maximum power consumption at around 7.5mW (14.4v x 0.515mA).  Considering the transmitter is supposed to put out up to 100mW, something is clearly not right.  As I mentioned in my previous post, the pulse amplitude may not be quite enough to drive the circuit to its intended power output.  The original Transroc had a matched set of components (R6, D2, Q4), and the parts list specifically states a replacement of any of these parts mandates replacing all three.  So this weekend I'll start there...playing around with the resistor to start (it appears smaller values for R6 would help pull Q4's base lower and therefore drive it harder), and then checking the voltage drops on my collection of 1N914's and B-E junction of the 2N5138's (the manual's Theory of Operation describes Q4 as acting as a comparator).





   
 

Offline Stray Electron

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #16 on: March 05, 2021, 08:33:15 pm »
Although I cannot provide you with any technical tips you don’t already have, as a model rocket enthusiast I hope you are successful with your project.
Back in the 60s, with the space race going at full speed, model rocketry was extremely popular.
We never built a radio finder, but did build a xenon strobe.


  X2! Chasing lost model rockets lead me into developing very small pyrotechnic smoke generators so that I could track them on the way back to earth and on the ground, up on people's roofs, in trees, etc!  All of that lead me into a career developing the real things; Pershing II, Canadian ADATS, US Hellfire, US Brilliant Pebbles.  It's been a hoot!
 

Offline fuzzoli

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #17 on: March 17, 2021, 10:53:35 pm »
I figured out the power problem.  The cheap breadboards have split power rails  |O (see yellow circles in the photo).  I'm not use to this layout as all of the "good" breadboards have the rails extended the full length of the board.  As "luck" would have it, the modulator section is on one power rail, while the RF section is on the other, so the modulator worked fine as is.  The low power output was due to power being supplied to the RF section through the modulator only.

After I added the wires to connect the rails (arrows), everything worked as expected!

...as Dave would say, "A trap for young players."

It turns out that I didn't actually notice the split rails as a wiring error.  When I hooked up the scope to the right side ground rail, all I saw was a noisy 60Hz sine wave.  That's what pointed me to an open ground as the most likely candidate.  THAT'S when I noticed the split rails!  |O

So we're back on track.  There's some strange behavior with the antenna matching coil that I'm discussing over here, but for the most part, I think the project is set to move to the next phase.

I'm keeping the current board for use with the breadboard, and will begin winding coils for a second board.  I also need to figure where to get the 3D parts printed.  Hopefully all will be ready for a late Summer test flight!
« Last Edit: March 17, 2021, 10:56:08 pm by fuzzoli »
 

Offline rdl

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #18 on: March 18, 2021, 01:24:37 am »
Actually, many larger breadboards (including the better ones such as 3M) have split rails like that. That's why the red and blue lines have a gap. 3M doesn't even provide any indication of this. Beware because some of them have the rails split into 3 sections. That really had me confused once.

I figured out the power problem.  The cheap breadboards have split power rails ...
 

Offline james_s

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Re: The Transroc: Cloning a 1970s Model Rocket 27MHz Telemetry Transmitter
« Reply #19 on: March 18, 2021, 02:44:26 am »
I don't think I've ever had a larger breadboard that *didn't* have split power rails. The only ones I've encountered that don't have that are small cheap ones. It's a feature, not a bug.
 


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