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Mr.RC-Cam

Vintage R/C Collection: The good old days

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Mr. RC-Cam,

I am working on an updated Sampey system and have read the article in Grid Leaks.

There is no other indication of timings but that the multiplex repetition rate can be from 15 to 40 Hz and that the throttle channel is 1100 Hz to 1200 Hz with 1150 Hz neutral.

Could you tell us what the actual frequencies of each channel are?

From the schematic values in Grid leaks, I figured that the multiplex rate is 32 Hz (8 ms per channel).

You also may be interested in my improved analog servo circuit as shown on Terry Tippet site:

http://myweb.tiscali.co.uk/norcimradiocontrol/Radio22a.htm

Thanks.

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The rep rate on mine is 14Hz.

Here is a list of the nominal channel tones:
 Motor: 1150Hz
 Elevator: 1800Hz
 Aileron: 2700Hz
 Rudder: 3600Hz

Nice work on the modernized analog servo. Are you designing your own retro-Sampey analog R/C system?

Speaking of retro designs, JR is introducing a vintage looking transmitter. Similar in appearance to Heathkit. And priced like they were in the 1960's.
http://www.jramericas.com/235042/JRP07432/

jr_colt.jpg.79f5644c192cea93e2130ba29efa

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It would be cool if JR sold the Colt's mechanical parts (case, sticks, etc) for DiY builds and at a practical price. They show these parts in their teaser images.

jr_colt2.thumb.jpg.d0e7add18b9ff64e0305f

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6 hours ago, Mr.RC-Cam said:

Are you designing your own retro-Sampey analog R/C system?

Yes, the projected solid-state discriminator circuit for one channel is attached.

This will output +0.48V with 3V p-p input square wave @ 1660 Hz and -0.48V @ 1970 Hz, neutral at 1800 Hz.

With <1300 Hz or >2500 Hz input, output is 0V. (Tested with LTSpice IV)

Dicriminator_Sampey.jpg

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Yes it would probably be quite easy to fit some modern TX components in to that case or even design your own.

I love valves/tubes but a tad large for airborne use :) transistors would be more in keeping with the spirit of the radio.

 

Terry

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The replacement 155T1 transistors arrived today and fixed the local oscillator problem. I also had to replace the RF preamp transistor and one in the I.F. stage.

BTW, the "bad" 155T1 transistors test OK on a semiconductor meter. My best guess is that the high frequency performance has deteriorated. FWIW, the 155T1 transistor was used in many early 1960's R/C receivers. It is no longer produced but the NTE160 substitutes are working well.

So the good news is that the receiver's "front end" is working. That is to say, the demodulated audio tones are seen at the input of the four discriminator (tone decoder) channels. But unfortunately the discriminator board is not working. So I have more work to do.

 

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It Works! I've dreamed of owning a functional Sampey 404 for many years so this is a major bucket list event. :)

I don't have official calibration instructions so I did my best. To re-align the A.M. receiver I followed the instructions I have for Controlaire's SH-20 receiver (it is nearly the same RF design). But I had to guess at calibrating the four commutation tones produced by the transmitter. If anyone out there has official Sampey 404 calibration instructions then please post them and I will follow the factory adjustment methods.

Despite their age all four servos work perfectly (no repairs needed). They are much slower than modern servos and have noticeable latency. But back in the early 1960's such things were not important issues.

So what does an old guy do with a functioning 50+ year old Sampey 404? Nothing really. It's just something a young boy dreamed of owning. That boy got really old, but he never gave up on the dream.

So this post marks the end to my Sampey 404 journey. As a parting gift here's an audio demonstration of Sampey's modulation technique for controlling four analog proportional channels: Click HERE to hear sampey_propo_tones.mp3

{FWIW, an audio amplifier was connected to the receiver's demodulated output. So what is heard are the four variable tone groups that are multiplexed onto the transmitted signal.}

One last beauty shot:

s404_1_1000.thumb.jpg.a185dfc8e37e0ec9bc

Edited by Mr.RC-Cam
Changed link to MP3 audio file.

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Nice job RC-Cam,

and thanks very much for the tone sample file.

If I had one to play with, I think I would have adjusted the position offset pots in the receiver to set the failsafe positions of the aileron, elevator and rudder servos to neutral first ( you mention that the throttle failsafe is okay), then once the failsafe was alright on all channels adjust the pots in the transmitter to these neutral positions.

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@jmp_blackfoot: I haven't figured out the correct failsafe adjustments. Upon signal loss the throttle goes low (good) and the elevator goes to neutral (good). But rudder and aileron command a turn (seems useful, but I don't think this is correct). The position offset pots in the receiver have a profound affect on servo symmetry and travel range, rather than simply control failsafe position.

That is why I am VERY interested in how the factory calibrated the system. This information may even be in the owner's manual. But other than the Grid Leaks magazine article, I have yet to find any useful Sampey 404 documentation. It would be awesome to have a scanned copy of the owner's manual or anything else that Sampey may have included with each sold system.

BTW, my transmitter has a push button switch next to the motor control knob. I did not know what it did because there is no mention of the push-switch in their advertisements or the Grid Leaks article. But now that the system is working I discovered it is a throttle cut switch.

s404_throttle_cut1_800.thumb.jpg.a13c676

There's an extra pot inside the transmitter for setting the motor servo position when it is pressed. When activated, rudder control is still available but elevator and aileron control are disabled (those two servos are neutralized).

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@Terry: Yes, satisfaction of epic proportions!

@jmp_blackfoot: Thank you for the B&D link, it helps confirm my suspicions. After more calibration attempts to solve the rudder/aileron failsafe issue, plus more troubleshooting, it appears the problem is due to the complementary transistors in the Yaw and Roll discriminators. These transistors need to be matched pairs and I suspect that age has affected them. I've decided to leave it as-is and just accept the failsafe oddity as an interesting quirk.

I mentioned earlier that my Sampey 404B receiver's RF deck closely matches Controlaire's SH-20 receiver. Although mine was factory produced, here's instructions on a DiY solution (seems to be the same Controlaire circuitry that Harry Sampey implemented in the 404B:
http://www.vintagercfiles.com/Magazine_Articles/Sampey/Sampey%20404%20modification%20-%20RCM%20June%2065.pdf

I'm still searching for Sampey Instructions. If I find them I will definitely share!

 

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Quote

Maybe the RC Hall of Fame Museum could provide a copy of these instructions?

Ed at RC Hall of Fame mentioned to me yesterday that he was sending a Christmas present by US Postal. :)

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Well, well, well, this sounds like an interesting present!

I did some more experimenting with the coder. Here is the result which works quite well.

All it takes is an ICM7555 Cmos timer, a PIC 12F508 controller, 5 resistors, 5 capacitors and the four control pots, simpler than I expected.

The clock input to the PIC sequencer from the 7555 tone generator ensures that switching occurs synchronous to the tone waveform.

With the values given, a variation of 10% of the center frequency is achieved (with control pots centered).

The 15k resistors are there to linearise the frequency response.

Also more interesting information on the similar Klinetronics system:

http://vintagercfiles.com/Files/Klinetronics/Klinetronics%20Astroguide.pdf

 

 

 

Codeur Sampey.jpg

Edited by jmp_blackfoot
Corrected omission in drawing

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I found an interesting article that describes microscopic hair growth (tin whisker) failures in old germanium transistors.
http://www.vintage-radio.com/repair-restore-information/transistor_transistor-faults.html

Maybe the transistor problems in my Sampey receiver were affected by this phenomenon.

 

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