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Who really invented Digital Proportional?

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Old 10-05-2010, 03:51 PM
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Default Who really invented Digital Proportional?

Why Digital Proportional for R/C was never patented by hobby manufacturers.

Many R/C manufacturers patented their creations, Howard Bonner held numerous patents on his escapements and servos. Why then is it nobody that we know of patented Digital Proportional, as it was a completely new concept in the field of radio controlled models? The actual facts are few and scattered, but fortunately there were enough clues to figure out what actually happened.

We start back in the very early 1960s at JPL in Pasadena Ca. before the formation of NASA. JPL was then top aerospace lab in the country. Jerry Pullen worked at JPL and was an avid R/C flyer and member of the Larks club, as was Doug Spreng. Spreng in his auto biography relates to us how he was interested in where Pullen had gained access to NPN transistors that were used in his proportional servos, and wound up working at JPL with Pullen to gain access to the advanced radio control system technology and components used in space craft.

As a result, Speng found out about what was then called Pulse Duration Modulation, (PDM) which we often now call Pulse Position Modulation (PPM) . This was the way signals were sent to control the many servos and switches in space craft like satellites and missiles. Borrowing the concepts of PDM, Spreng built a small version of a PDM feedback servo amplifier, and then proceeded to make a PDM transmitter and receiver for use in a model plane with the assistance of Don Mathes, who was skilled in RF design. Their joint efforts ultimately resulted in a hobby radio system they called the Digicon, which was the first of it’s type to use the PDM technology they “borrowed” from JPL; pirating would actually be a more appropriate, but unflattering description however.

Although the Digicon prototypes worked well initially, some of them began to experience loss of control. It was eventually determined with the aid of Frank Hoover that the problem was the transmitted RF carrier was only on during the pulses, allowing interference to overcome the receiver during the long “sync” pause between pulse frames. Spreng and Mathes had made one critical mistake, but it was easily rectified by inverting the modulation pulses in the transmitter to keep the RF carrier on most of the time and only shut off during the short 250 microsecond pulses, thus keeping the receiver “locked” onto the signal 95% of the time and not allowing noise in. Unfortunately however, the Digicon never recovered from it’s initial bad reputation in spite of the fact that it was revised and updated, Mathes and Spreng therefore sold the design to Bill Cannon, who re –released it a few years later as the C&S Digicon II.

In the mean time, Frank Hoover of F&M and Larson/Kagele of Bonner Specialties had released their first versions of PDM “digital proportional” as these systems were then so named, but they all used analog type servos. None used the PDM feedback servo Spreng had made, which was superior. Kraft was backing Jerry Pullen in the design of his own proportional system, which oddly did not use PDM technology in the Tx/Rx or servos. Why then did all these manufacturers not utilize the PDM feedback “digital” servos?

Hoover points out that the technology in his F&M was a version of PDM as used for missiles and satellites, providing an important clue: everyone knew this technology had been “borrowed” from JPL, and as such nobody wanted to risk any possible investigations from the government as to how they had gained access to what was then considered classified information. It was the servo technology that presented the problem, it was classified. Spreng did not stay long at JPL, but Pullen stayed on longer, and was not willing to risk his job “borrowing” classified technology for his hobby project proportional radio. This explains why Pullen spent so many years unsuccessfully trying to develop an analog proportional hybrid radio of his own design. By late 1965 however, it became apparent that the government, and then the newly formed NASA was not interested in going after R/C companies that were using the PDM technology, largely due to the fact that many people within the space agency were model aviation enthusiasts themselves and sympathetic towards the development of reliable multi-channel proportional radios for the R/C hobby.

This then led to the flood gates being opened in terms of companies that started producing PDM type feedback servo systems called “Digital Proportional” Kraft, Pullen and others then quickly abandoned all previous designs and “digital” became the standard. Bill Cannon was quick to release his Digicon II ahead of most the of the competition once he saw using PDM servos was not going to be a legal problem.

And so we see nobody could really lay rightful claim to a design which had been smuggled out of JPL, and in fact whoever the did develop it had signed the patent rights over for a buck to the government, as was typical practice when working for them in development projects. If the government paid for the research, they owned the designs that came out of it. Therefore it would not only have not been a crime to pirate this technology, which could be considered espionage, but further more, who would be foolish enough to document that deed by filing a patent application for something the government already owned? In actuality, Spreng and Mathes took a calculated risk; they gambled Jerry would keep quiet, which he did and that they would be under the radar. Plus they knew NASA was going to be soon taking over the space division of JPL and were counting on that shake up preoccupying the two agencies and any focus on them therefore being diverted in the process. But they were a little too quick in releasing the Digicon, and as a result others were able to cash in on the technology once it was determined the “coast was clear” and there would be no investigations from the government. This is why nobody was able to corner the market on digital/DPM, as it was not patentable.
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Old 10-05-2010, 07:36 PM
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Default RE: Who really invented Digital Proportional?

Hi Jaymen.

That was one of the most informative posts I've seen to date on the history of the digital system... Very good!.... Enjoyed
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Old 10-06-2010, 11:11 AM
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Default RE: Who really invented Digital Proportional?

I was disscussing this with an old boss of mine from Airtronics, we both had worked with Dog Spreng in the early 1980 at a robotics company, and he and Doug often went out to the 19th hole of the local golf course for a 2-martinin lunch and Doug related something to him:

Pullen got Spreng the job at JPL specifically for the purpose of getting the technology they needed to build an advanced proportional guidance system for model planes. It was a covert and well orchestrated plan. Doug would gain access to the information, while Jerry would feign no knowledge of what he was doing and continued on with his developement at home of an analog proportional. Jerry was not willing to risk his job pirating the information, but was willing to assist a fellow modeler in gaining access to it. The pay-off for Jerry was he would then be given the technology.

The other part of the deal was that if a bunch of companies all had products of similar design, and used the same technology, the knowledge would then be considered to be in the public domain, and therefore anyone using it would not be prosecuatble. This was the cover they came up with to protect themselves once they had absconded with the PDM secrets from JPL. Spreng, and Mathis sold their services to quite a few R/C manufacturers, Orbit, Deans, Kraft, Cannon, F&M, Bonner, and others as well. This was part of the plan too, as they found it was safer to sell their services as designers than to start a company. To further insulate themselves, but also make more money they formed Micro Avionics, and the inner workings and ownership remained a secret as in fact the back door deal was made with the Dunhams: Spreng would give them the pirated technology so Orbit could make Digital radios in trade for the Dunhams setting him and Mathes up in business making radios of their own brand, and supply all the cases, hardware, gimbals, servos, connectors and batteries such that only the PC boards were different. The actual ownership of Micro-Avionics and it's close relationship to Orbit was kept a secret to insulate Spreng and Mathes as they were very worried about being investigated for how they came up with this new technology which was previousely kept secret at JPL. Additionally, it served a purpose for the Dunhams as well because they now had a second company to market the radios directly to the customer, eliminating the distributor and dealer mark ups, meaning they could sel the "econo" version without their name on it at a higher price.

It is also quite obviouse in retrospect that Pullen was in on this deal too, because as soon as the cat was out of the bag so to speak(the Digicon) he went hot and heavy into it with Phil Kraft and they quickly did exactly what the Dunhams had done and formed PCS. He left JPL and then cashed in his chit with Spreng and Mathes who gave him the schematics and design concepts so he could build a version for Phil.

Having "floated" the Digicon to test the waters, Spreng and Mathis then sold it to Cannon, and rather than remain high profile as a company manufacturing radios, they chose to work behing the scenes peddling their services to all the other R/C companies and stay low profile in case the government got wind of the hobby industry using classified technology. Their thinking was it was safer, and would require less effort on their parts to quitely go behind the scenes and sell the technology, as oposed becoming a manufacturer and competing with eveyone else. It was a well laid plan that worked out for everyone and funny how they were all Larks club members huh?

How is it that everyone came up with digital systems all with a year of each other that were essentially all the same design concept? It's because Spreng and Mathes sold their services and information to everyone and made good money doing it, while insulating themselves at the same time.
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Old 10-06-2010, 11:46 AM
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Default RE: Who really invented Digital Proportional?

Great history Jay,

I knew some of those folks, Pullen & Werick especially. But I wasn't aware of what was going on at the time. My first proportional was a Bonner 4RS. Always thought that the 4RS was sort of a "second generation" system, but the servos were very poor. They did have feedback pots, but would you consider them to be true digitals ? I soon replaced the Bonner servos with Controlaire S4's, which where vastly superior. I don't know who designed the Controlaire stuff.

People used to talk about the weakness of the Harmonic Drive in the 4RS servos. But my biggest complaint was the fact that the servos caused reduced radio range. With one servo connected, the antenna off range was maybe 20 feet. Plugging in additional servos incrementally reduced range until with four servos the antenna off range was only 2 or 3 feet. Thus with all four servos in an airplane one had to be very careful not to taxi out too far or you couldn't turn around to begin the takeoff. And look out if you took off directly away from yourself or you would go out of range before you got airborne !

The Controlaire servos really fixed the short range problem. Do you think this was simply better motor noise suppression of better servo circuitry?

Dick Fischer
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Old 10-06-2010, 03:25 PM
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Default RE: Who really invented Digital Proportional?

Jay,

After further reflecting on your most interesting article, another memory popped up. Sometime in the mid 1960's I was told that Jerry Pullen was the "brains" behind all of the digital proportional radios that were then coming onto the market. From what you have said, perhaps it would have been more accurate to say that Jerry was the "source".

Dick
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Old 10-07-2010, 02:01 AM
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Default RE: Who really invented Digital Proportional?

Excellent summary Jay! One minor error - NASA was formed on July 29, 1958 replacing the previous NACA. Did you get my email on the Testor's Simpulse new RX you sent me? Russ Farris
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Old 10-07-2010, 05:11 PM
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Default RE: Who really invented Digital Proportional?

The servos used in the first Bonners were analog feedback types that used a pulse to voltage converter. The incomming pulse was converted to a voltage and compared with a voltage on the feedback pot to determine if the servo was tracking.

The range went down due to the high current draw of the harmonic servos, it dropped the battery voltage which reduced the receivers range, and additionally, each servo motor makes some noise which also can affect range.

The Controlaire S-4 was a true digital type PDM type, and was more current efficient than previous designs like the 2nd generation 4-RS. The 4-RS lacked failsafe, had a much more simplified and conventional encoder and decoder, and a small receiver with the first integrated circuits to ever be used in an R/C hobby radio.

JPL was where most of the NASA projects were done early on, including Explorer I, it was the biggest and premier developemental lab for space borne craft at that time, as it was part of Cal-Tech and it's founder Jack Parsons also had a hand in Aero-Jet company as well. I meant to say that by the mid 1960s, NASA had many other facilities come on line to expand their capabilities so JPL was lo longer their sole source of technology, but was still one of the top ranked labs in the world. Thanks for clarifying the dates, it's good to know them.

One can see that our hobby uses technologies and devices created for much larger markets, we get the low cost benefits of that as these technologies are mass produced in volume and we reap the cost benefits. If hobby radios were designed from the ground up with specialized technology intended soley for model radio control, the cost to us the user would be astronomical due to the initial design and investment, and relatively low sales number of manufactured radios, as R/C is a small niche specialty market.

Thus we are tied to hip with the state of the art technical developements and have to rely on spin-offs of those technologies to trickle down to us in order to have affordable radios for models. In the above case, we see how creative, sly, and determined a couple dedicated modelers were at geting that technology for the rest of us, and they took some risky steps in the process, no doubt not only for the hobby, but for financial gain as well...can you really blame them?

When I worked with Doug Spreng in 1982-3, he would always get quiet and not say much, or change the subject whenever I brought up him being the grand daddy of digital, and now I know why he was not very forthcoming, and also why he shied away from accepting acaldes and credit for it.
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Old 10-07-2010, 05:15 PM
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Default RE: Who really invented Digital Proportional?

Russ, I did not get the e-mail, forward it to: techservice@newmarpower.com
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Old 10-28-2010, 11:41 AM
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Default RE: Who really invented Digital Proportional?

Hi

thought you might be interested in this site Radio Control Hall of Fame

http://www.rchalloffame.org/index.html

Currently have the following planes which I have had for a long time

Taurus
Mambo
Esquire
Sportmaster

Take care and have fun
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Old 10-28-2010, 05:16 PM
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Default RE: Who really invented Digital Proportional?

I think I seen this site once before ...smaller though. Loved the ability to zoom in real close. I've had or flown, Orbit,WE Expert,Kraft open gimbal, Heathkit, Ace, Cox , Airtronics, Hitech, Blue Max, some old tone gear (can't rem name) a Venus reciever on 27, Futaba, Tower, and maybe a few others I trained owners on.

This is quite a site and collection with well laid out searches on every mfg and model..

Great find!!
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Old 10-29-2010, 07:18 PM
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Default RE: Who really invented Digital Proportional?

ORIGINAL: gittarpikk

I think I seen this site once before ...smaller though. Loved the ability to zoom in real close. I've had or flown, Orbit,WE Expert,Kraft open gimbal, Heathkit, Ace, Cox , Airtronics, Hitech, Blue Max, some old tone gear (can't rem name) a Venus reciever on 27, Futaba, Tower, and maybe a few others I trained owners on.

This is quite a site and collection with well laid out searches on every mfg and model..

Great find!!


I was thinking that back when a few years ago, there was yet another group that was centered in the Sou. Calif. area and dealed with same materials. But these guys were quite old, and secretive. They used to have theirown web site years ago (gone now) as I remember they said.


What was their official name they used?


Wm.
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Old 10-29-2010, 09:35 PM
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Default RE: Who really invented Digital Proportional?

Unless is the same one, I don't remember that one.

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Old 11-01-2010, 06:24 AM
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Default RE: Who really invented Digital Proportional?

And I was so sure that Al Gore said HE invented digital propo. Mitch
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Old 12-04-2010, 01:33 AM
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Default RE: Who really invented Digital Proportional?


ORIGINAL: nine o nine

And I was so sure that Al Gore said HE invented digital propo. Mitch

Thats so funny. I thought the same thing as I read the title of this thread.. <Other than what I was thinking. there is allot of interesting info here.
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Old 12-04-2010, 08:09 AM
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Default RE: Who really invented Digital Proportional?

nine o nine and TripleDeucer. Great minds run in the same direction. I had exactly the same thought about Gore, as soon as I saw the question, but you guys beat me to it:-)))))))))))

Les
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Old 12-27-2010, 08:49 PM
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Default RE: Who really invented Digital Proportional?

After Graduating from high school, I went to work for Kraft Systems as the shipping clerk in August 1964. I remember Phil Kraft & Don Mathes working daily on refining the KP-4. Jerrry Pullen worked on another design. The company was shipping Reed and single channel transmitter/receiver combinations. After Don Mathes left, the company began shipping KP-4 proportional radio's and moved to a larger building. The PCS-5 was built there until they decided to assemble them in their own building. I later worked for Micro Avionics & Orbit Electronics.

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Old 03-22-2019, 04:51 PM
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Jerry K
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I have been to Jerry's & Bill's house many times to repair my PCS & Cannon systems. I went from PCS to Cannon to Kraft. That was when we had real linear servos not these rotary things that have built in expo.

AMA 7082.
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