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I've just learned that the modelling fraternity has lost yet another of its pioneers - Doug Spreng.
Doug was an American, and he wasn't a helicopter man - but every time you switch on your receiver in your model, you are using technology that he pioneered. Doug was the inventor of the digital pulse tracking servo amplifier.
Back in the early 60's, mutli-channel radio control was either "bang-bang" systems, where the controls went over to full deflection when a switch was moved, or analogue proportional, more like the systems we have today. The analogue systems were generally reliable, but suffered from two major drawbacks. Firstly, the response time was slow, and secondly the neutrals were prone to drift with temperature and voltage. There was also a smaller problem in that for small corrections, not much voltage was applied to the servo motor, meaning that it lost accuracy under load.
Doug Spreng thought long and hard about this, and came up with a system where instead of comparing voltages, he compared pulse widths! At a stroke, he had eliminated servo lag and drift! As a side effect, the servo motor received full voltage, even for the smallest errors, which also eliminated the loss of accuracy under load!
He chose a variable pulse width of 1-2 mS, and a repetition rate of 50-60 Hz! It says much about his genius that we are still using those figures today, nearly 60 years on!
Doug teamed up with Don Mathes to produce the world's first digital proportional radio system, the Digicon. Not only was it unique in being digital, rather than analogue, but it also introduced the "twin-stick" transmitter layout that we still use today. Prior to this, most systems were single stick "cuddle-box" layouts.
Like most pioneering systems, the Digicon had its problems. The method of imposing the pulses on the radio signal that they chose left the receiver wide open to interference, and caused problems in the design of the Automatic Gain Control circuit necessary in AM systems. It was Frank Hoover of F&M (another major American manufacturer of the era) who suggested the "spike-off" modulation system to Spreng and Mathes, who recalled all the systems they had made, and modified them free of charge. This solved the problem, but by then, the Digicon's reputation was shaky, and they were soon in financial difficulties. They were taken over by C&S (later Cannon) who continued to produce modified Digicons with great success.
Its worth noting that neither Spreng nor Hoover patented their ideas, and never made any money directly from them. This allowed others to build freely on their work, resulting in the highly reliable systems we enjoy today! Indeed, when digital integrated circuits first came on the market, the Hoover "spike-off" modulation system proved ideally suited, allowing very simple decoders to be made using very cheap components!
In the late 60's Doug came to England at the invitation of Harry Brooks, and designed the Sprengbrook "red box" radio. This was probably the most reliable radio of the era, and I still have mine! Later Sprengbrooks were re-badged German Microprop units, and never seemed to be as consistently reliable as the Spreng designed outfits.
After leaving Harry Brooks, Doug went to work for Staveley, producing the Staveley Digital system, to replace their earlier analogue design. During this time Doug continued to fly competitively in F3A (fixed-wing) aerobatics, and as a former US National Champion, certainly set the standard in the UK!
Eventually he tired of England's cold and damp, and returned to the US, where he joined Kraft. He was largely responsible for the Kraft "Signature" series radios, in their day, the "Rolls-Royce" of RC systems.
The AMA have an appreciation of Doug Spreng:
https://www.modelaircraft.org/files/SprengDoug.pdf
There is also a very good history of the pioneering Digicon system, as well as many other early systems, at the RC Hall of Fame website:
Radio Control Manufacturer: Digicon
The main index is at:
Radio Control Hall of Fame
--
Pete
Doug was an American, and he wasn't a helicopter man - but every time you switch on your receiver in your model, you are using technology that he pioneered. Doug was the inventor of the digital pulse tracking servo amplifier.
Back in the early 60's, mutli-channel radio control was either "bang-bang" systems, where the controls went over to full deflection when a switch was moved, or analogue proportional, more like the systems we have today. The analogue systems were generally reliable, but suffered from two major drawbacks. Firstly, the response time was slow, and secondly the neutrals were prone to drift with temperature and voltage. There was also a smaller problem in that for small corrections, not much voltage was applied to the servo motor, meaning that it lost accuracy under load.
Doug Spreng thought long and hard about this, and came up with a system where instead of comparing voltages, he compared pulse widths! At a stroke, he had eliminated servo lag and drift! As a side effect, the servo motor received full voltage, even for the smallest errors, which also eliminated the loss of accuracy under load!
He chose a variable pulse width of 1-2 mS, and a repetition rate of 50-60 Hz! It says much about his genius that we are still using those figures today, nearly 60 years on!
Doug teamed up with Don Mathes to produce the world's first digital proportional radio system, the Digicon. Not only was it unique in being digital, rather than analogue, but it also introduced the "twin-stick" transmitter layout that we still use today. Prior to this, most systems were single stick "cuddle-box" layouts.
Like most pioneering systems, the Digicon had its problems. The method of imposing the pulses on the radio signal that they chose left the receiver wide open to interference, and caused problems in the design of the Automatic Gain Control circuit necessary in AM systems. It was Frank Hoover of F&M (another major American manufacturer of the era) who suggested the "spike-off" modulation system to Spreng and Mathes, who recalled all the systems they had made, and modified them free of charge. This solved the problem, but by then, the Digicon's reputation was shaky, and they were soon in financial difficulties. They were taken over by C&S (later Cannon) who continued to produce modified Digicons with great success.
Its worth noting that neither Spreng nor Hoover patented their ideas, and never made any money directly from them. This allowed others to build freely on their work, resulting in the highly reliable systems we enjoy today! Indeed, when digital integrated circuits first came on the market, the Hoover "spike-off" modulation system proved ideally suited, allowing very simple decoders to be made using very cheap components!
In the late 60's Doug came to England at the invitation of Harry Brooks, and designed the Sprengbrook "red box" radio. This was probably the most reliable radio of the era, and I still have mine! Later Sprengbrooks were re-badged German Microprop units, and never seemed to be as consistently reliable as the Spreng designed outfits.
After leaving Harry Brooks, Doug went to work for Staveley, producing the Staveley Digital system, to replace their earlier analogue design. During this time Doug continued to fly competitively in F3A (fixed-wing) aerobatics, and as a former US National Champion, certainly set the standard in the UK!
Eventually he tired of England's cold and damp, and returned to the US, where he joined Kraft. He was largely responsible for the Kraft "Signature" series radios, in their day, the "Rolls-Royce" of RC systems.
The AMA have an appreciation of Doug Spreng:
https://www.modelaircraft.org/files/SprengDoug.pdf
There is also a very good history of the pioneering Digicon system, as well as many other early systems, at the RC Hall of Fame website:
Radio Control Manufacturer: Digicon
The main index is at:
Radio Control Hall of Fame
--
Pete
V-Bar x2
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