jaymen

In reading the 1963 issues of AM I came across an interesting paragraph and photo of Jerry Pullens proportional transmitter he was developing with and for Phil Kraft. Nate Rambo of Camarillo Ca reported the system was a revised version of the one that had been in development and flying for 2 years, this would then date it's initial flying debut somewhere in the spring of 1961. It appears to be a 3 channel system, and a toggle switch on the upper right side appear to be a positionable throttle control.

What is surprising is that Nate mentions Orbit has stopped work on the Pullen and started on their own multi-propo design. He goes on to mention the Spreng-Mathis team would be ready to release the Digicon for sale by the time the article was published.

This then means that the Pullen proportional was being worked on by Kraft, and Orbit at the same time, along with input from Spreng and Mathis, as they worked with Jerry at JPL at one point. For some reason all these guys thought they could come up with a better analog multi propo system than Space Control, which they failed to do over a 4 year span. Ultimately, Orbit's first multi propo was a transistorized Space Control, some called them "Orbitrols" , and this occured once Zel Ritchie handed Space Control over to the Dunhams of Orbit.

The main reason digital proportional systems for R/C were such a long time in the making was simple: Cost. Transistors at that time were expensive and not very consistant, thus a stable design require quite a few transistorized stages, many more so than multi, or analog systems. This meant that they could be produced but the costs would be prohibitive. Ironically, right about the time cheaper silicon transistors became availlable and everyone had a digital proportional radio on the market, the first consumer grade integrated circuits were released, obsoleting all the first generation digital propo designs!

The advantage integrated circuits offered were several fold: 1. Huge cost reduction of the price per each individual transistor stage as an IC of the era contained up to 100 or more transistors. 2. As all the transistors in an IC were on the same chunk of silicon, they had almost identical characteristics, making matching them a thing of the past, this resulted in much more consistant and stable circuit opperation. 3. The intergration of many solid state devices into one package eliminated allot of wiring and simplified not only design, but assembly time, reducing costs drastically.

There was well rooted firm beleif in the early 1960s amoungst the R/C propo designers that simple was better, not only in terms of cost, but reliabilty. This goes back to the concept of fewer parts means less to go wrong. Analog was a well understood technology at the time, and all the electronic components of the era were specifically for analog, hence they worked quite well. The problem came when the first generation transistors were pressed into service doing high speed switching as required by digital technology, they just were not quite good enough, and digital technology had a whole new set of issues beyond what the designers had experienced with analog. Add to that the fact they were in new uncharted territory where there was nobody elses experience to fall back on and one can see why it took them so long to get it right.

At the end of the era, nobody ever really surpassed Space Control with a better analog system, it was prooven out in the end to have been the best as it was copied by ACL and eventually built by Orbit in a transistorized version. Even the first digital propo sets of 1963-65 could not match it in terms of cost and reliability, that is how mature analog technology was. It took the integrated circuit, developed in multi-million dollar high tech labs, to bring digital proportional to the forefront.

HighPlains

My Feedback: (1)

Audio tones have been sent by radio since nearly it's inception. By the time the early analog work of Al Doig's "ULTI" sytem in '58-59, reed radios had been built for a decade. One on the main advantages of sending tones is that they make the radio link rather resistant to noise. The only real change between a reed radio and the early analog was making the tones variable and building a discriminator small enough to carry in the model for each channel. Pure analog servos were crude and so easy that even a caveman could build one.

Prior to the commercial advent of the transistor, gain was a very difficult thing in terms of size, weight and power consumption. But from the late 50's on, it has been one hell of a ride.

What would be interesting is to revisit the analog RC system with today's technology. I suspect that performance equal to any digital system could be met.

jaymen

One must realize that Spreng, and Mathis, in fact the whole JPL crowd had an elitest attitude, they talked down everyone elses efforts as not good enough, nit picking them to death despite the fact they themselfs at the time had done no better, having failed miserably at first. The reality was you had some very big egos trying to out do each other and nobody was admitting their own limitations, or willing to give the other guy credit. The result was allot of missconceptions and half truths being spread within the R/C community about the shortcomings of Analog proportional that were downright wrong. This type of snobbery an non-sense exists today amoungst some of the top competitors in R/C, and other venues, it comes with the territory. It pains me to see it still being re-counted incorrectly after all these years, but then again, the sources it comes from are the same so it's no surprise. It would be nice to see the more impartial brutal truth side of this story told on RCHoF because that is what really happened. It may not be flattering, but then again, the truth often isn't.

ukengineman

Here in the UK the first commercial full house proportional system was the RCS Tetraplex. Since I saw Don Brown flying his Quadruplex system at the 1962 World Championships held at RAF Kenley, Surrey, UK I knew I wanted a proportional system. A few people imported Space Control into the UK but it was extremely expensive and I was a student studying electronics. RCS was the largest manufacturer of R/C in the UK in the 1960's and their first proportional system was the Tetraplex, I got one as soon as I had the money together. It was an all transistor analog system and worked on exactly the same principal as Space Control. I don't think they copied any of the circuitry but they certainly copied the method of operation. See attached period advert. The infuence of Space Control had crossed the Atlantic. It was a short lived product as they soon replaced it with a digital system influenced by the F&M Digital 5. After RCS ceased production they asked me if I would service them which supplemented my student grant. I still have a few parts including a Tx encoder board.
Alan

ukengineman

Highplains, your comment about revisiting analog systems with modern technology is interesting. I am sure that the drift problems could easily dealt with but there was another reason for the eclipse of analog systems by ppm digital and that is bandwidth. With a pure analog system more channels means more bandwidth and even with the channel spacing of the 1960's it was a problem. With a ppm digital system more channels did not alter the bandwidth, it just increased the latency.
Alan

JMP_blackfoot

Back in 1987, I spent some time refining analog servo circuitry. The end result is shown here. At first glance, the circuit seems to be the usual four-wire analog servo amplifier, but there are two main differences.
Fist, the amp-op on the left makes sure that the feedback pot is supplied with absolutely symmetrical voltage. This completely eliminates neutral drift in the servo itself.
Second, the extra components R4 and C2 dramatically change the behaviour of the circuit.
R4 makes the output stage (T1 to T4) behave like a double Schmidt trigger (output transistors are either off or fully on) and introduces a controlled dead band while C2 defines a minimum conduction time to the motor. thus the motor is fed full voltage pulses already with the slightest input voltage difference.
Parameters like deadband and minimum conduction time (pulse width) are adjustable via component value change.
The amplifier behaves much like a digital servo amplifier. In my implementation into Logictrol mini servo mechanics, the following results were obtained:
Input range : +/- 0,4V
Deadband : +/- 1,75 mV (= 0,4%, equivalent to an 8-bit digital resolution)
Minimum conduction time : 3,5 ms
Holding torque and general performance equal to digital servo.
This circuit was published in "Wireless World" Magazine at the time.
I can explain the operation of the circuit in more detail if anyone is interested.