Thanks for the link, it was really interesting viewing. I hadn't realised that Flight Link had more than the basic 4 channels back then and that scale aircraft of the era had retracts. I've downloaded the video as an mp4, so if it is removed from 'face ache', I can upload to YouTube.
Thanks
Mike
Flight Link 2+1 Analogue Proportional
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Mike_K
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Pchristy
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Re: Flight Link 2+1 Analogue Proportional
I'm not sure that FlightLink ever had more than four channels. Even four channels was difficult to manage with an analogue system. Kraft tried for years to get the Pullen system in to production before giving up and switching to digital. Making a one-off prototype is one thing - successfully mass producing them, something else.
The only 5 channel analogue system I recall seeing advertised was the Sampey Starlight, which I don't believe was ever sold in the UK, and I don't recall any mention of it being used in anger even in the US.
Where analogue did score was in interference rejection - especially such things as metal-to-metal noise, to which a lot of early digital systems were susceptible. However, in just about every other way (accuracy, freedom from drift, speed of response) digital was so superior that analogue very quickly fell out of favour.
From a production point of view, one of the biggest headaches of an analogue system was that it wasn't easy to "re-use" circuitry. Each part of the encoder and decoder was pretty much unique to the channel for which it had to be designed. Digital, on the other hand, allowed the same basic circuit to be "daisy-chained" - a bit like Lego bricks - to enable almost as many channels as you wanted! And once the price of digital integrated circuits fell to a practical level, it really was "game-over" for analogue.
That didn't stop people from using things like micro-switches at extreme throttle travel (for instance) to actuate retracting undercarriages and the like. I suspect that is how the system in the film worked, though I stand to be corrected.......
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Pete
The only 5 channel analogue system I recall seeing advertised was the Sampey Starlight, which I don't believe was ever sold in the UK, and I don't recall any mention of it being used in anger even in the US.
Where analogue did score was in interference rejection - especially such things as metal-to-metal noise, to which a lot of early digital systems were susceptible. However, in just about every other way (accuracy, freedom from drift, speed of response) digital was so superior that analogue very quickly fell out of favour.
From a production point of view, one of the biggest headaches of an analogue system was that it wasn't easy to "re-use" circuitry. Each part of the encoder and decoder was pretty much unique to the channel for which it had to be designed. Digital, on the other hand, allowed the same basic circuit to be "daisy-chained" - a bit like Lego bricks - to enable almost as many channels as you wanted! And once the price of digital integrated circuits fell to a practical level, it really was "game-over" for analogue.
That didn't stop people from using things like micro-switches at extreme throttle travel (for instance) to actuate retracting undercarriages and the like. I suspect that is how the system in the film worked, though I stand to be corrected.......
--
Pete
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Mike_K
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- Joined: 16 Feb 2018, 06:35
- Location: Hertfordshire
Re: Flight Link 2+1 Analogue Proportional
Pete
Thanks for clarifying how many channels the older sets had. I think Flight Link were analogue to the end or did they go digital? The reason I ask is that I have a later Flight Link Sovereign single stick set with what appears to be two auxiliary channels. That makes five channels in total (Ail, Ele, Rud, Aux1, Aux2).
Phil_G says Idris Francis is still about, maybe we could get Phil to ask him directly?
Mike
Thanks for clarifying how many channels the older sets had. I think Flight Link were analogue to the end or did they go digital? The reason I ask is that I have a later Flight Link Sovereign single stick set with what appears to be two auxiliary channels. That makes five channels in total (Ail, Ele, Rud, Aux1, Aux2).
Phil_G says Idris Francis is still about, maybe we could get Phil to ask him directly?
Mike
- Flight Link single stick with two auxiliary channels
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Pchristy
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- Location: South Devon, UK
Re: Flight Link 2+1 Analogue Proportional
Mike, the original FlightLink was essentially a closed-loop "Galloping Ghost" system, with mark/space for one channel and rate for the second. The throttle was operated by giving full "on" or "off" commands, during which times the main controls were non functional. (A 2+1 system)
I'm not sure how they managed the four-channel system, but Space Control (and the later Orbit analogue system, which was just a transistorised Space Control) as well as the RCS Tetraplex did it by using two tones alternately. The mark/space provided one channel, the rate a second and the frequency of the two tones two more channels. Some other systems (Sampey?) used four tones in sequence, with a counter at the receiver sending each one to the appropriate discriminator in turn.
With the mark/space system, it was very difficult to add any more channels, though it might have been possible to alternate the output of a low priority channel to two servos. I notice your FlightLink has the extra channels set for twin throttles (?) which would support the sharing idea.
Aside from the drift problems, the other issue facing analogue systems was that to discriminate reliably the frequency of the "tones" requires around ten cycles to be measured. This seriously limits the maximum rate at which you can alternate them, leading to quite a bit of latency in the response times.
Mind you, back then, the servos were pretty slow anyway, which disguised the issue quite a bit! You wouldn't believe how slow my Digimite servos are!
Latterly, many PCM systems on 35 MHz did a similar sharing technique for the auxiliary channels, only transmitting them ever other, or every third frame, in order to try and improve the latency inherent in narrow-band PCM.
It would be interesting to hear what Idris Francis has to say on the subject. I never owned a FlightLink system, but one of their demo pilots belonged to the club to which I belonged at the time, and several others bought them too. All had problems with drifting trims, as well as throw which appeared to vary with range (!), but the radio link itself seemed solid enough.
Interestingly, the only time my Digimite ever fail-safed was when a FlightLink transmitter got between me and my model! This was repeatable! The radio recovered as soon as it emerged from the shadow of the Flightlink Tx, but after that, I never flew if a FlightLink was in operation at the same time.....!
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Pete
I'm not sure how they managed the four-channel system, but Space Control (and the later Orbit analogue system, which was just a transistorised Space Control) as well as the RCS Tetraplex did it by using two tones alternately. The mark/space provided one channel, the rate a second and the frequency of the two tones two more channels. Some other systems (Sampey?) used four tones in sequence, with a counter at the receiver sending each one to the appropriate discriminator in turn.
With the mark/space system, it was very difficult to add any more channels, though it might have been possible to alternate the output of a low priority channel to two servos. I notice your FlightLink has the extra channels set for twin throttles (?) which would support the sharing idea.
Aside from the drift problems, the other issue facing analogue systems was that to discriminate reliably the frequency of the "tones" requires around ten cycles to be measured. This seriously limits the maximum rate at which you can alternate them, leading to quite a bit of latency in the response times.
Mind you, back then, the servos were pretty slow anyway, which disguised the issue quite a bit! You wouldn't believe how slow my Digimite servos are!
Latterly, many PCM systems on 35 MHz did a similar sharing technique for the auxiliary channels, only transmitting them ever other, or every third frame, in order to try and improve the latency inherent in narrow-band PCM.
It would be interesting to hear what Idris Francis has to say on the subject. I never owned a FlightLink system, but one of their demo pilots belonged to the club to which I belonged at the time, and several others bought them too. All had problems with drifting trims, as well as throw which appeared to vary with range (!), but the radio link itself seemed solid enough.
Interestingly, the only time my Digimite ever fail-safed was when a FlightLink transmitter got between me and my model! This was repeatable! The radio recovered as soon as it emerged from the shadow of the Flightlink Tx, but after that, I never flew if a FlightLink was in operation at the same time.....!
--
Pete
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Mike_K
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Re: Flight Link 2+1 Analogue Proportional
Pete
While looking through old RCM&E mags for a review of the Graupner Caravelle (which I haven't found yet) I came across an advert for Flight Link (Sept 68) showing a "five servo system", so they were available. I've got a Rx for the FL single stick Sovereign I'll have to check how many servo leads there are (I know I've only got 4 servo's).
Mike
While looking through old RCM&E mags for a review of the Graupner Caravelle (which I haven't found yet) I came across an advert for Flight Link (Sept 68) showing a "five servo system", so they were available. I've got a Rx for the FL single stick Sovereign I'll have to check how many servo leads there are (I know I've only got 4 servo's).
Mike