RE: PPM, PCM ?
Ive personally seen a case at FL jets where an aircraft on the downwind and went into failsafe. The turbine shut down and pilot had no control. The receiver did what it was supposed to do and the aircraft continued to fly straight. The plane was headed for Tampa, but all of a sudden control was regained and the Kingcat glided all the way back and made the runway. ECU showed over a 2 second failsafe and everything was as advertised. I dont know that in this case if it were a PPM that the aircraft would have continued to fly straight because of the servos glitching. Cats have 9 lives...that one has 8 left.
Mike |
RE: PPM, PCM ?
As a real field experiment, My P-80 powered Kangaroo with a PPM futaba normally has 0 hits each flight. Sometimes (every 6 flights or so) I got 1 hit of .2 or .1 seconds... and it never shows off in the plane´s reactions, (believe me, I fly this plane fast and close to the ground, so I would see it).
And all this with a club field full of fiery glow powered planes and helicopters trying to tune it´s engines on ground while I am flying, nor to talk about the r/c cars, the cell phones, the broadband over power lines, and sun flares! ;) |
RE: PPM, PCM ?
That's amazing, evry PPM hit I have seen causes massive servo movement.
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RE: PPM, PCM ?
Well I think that a 0.1 or 0.2 second glitch the plane wouldn´t have time to wobble at all, or if you are flying a PCM receiver, you wouldn´t notice that you didn´t have command on the plane for such a short period.... anyway I flew this same receiver in a F3A airplane airplane for a year and based in this confidence I installed it on the roo.
But although i am currently safely flying a PPM receiver on the roo, I would instead prefer to use a PCM receiver on it, like I said before,because if it is properly setup, you can do something if you got a massive hit, and not because PCM reception is better than PPM .... |
RE: PPM, PCM ?
ORIGINAL: Gerald Rutten I was always teached that if something works, don´t mess with it!!! Cheers, Gerald |
RE: PPM, PCM ?
ORIGINAL: specialFX ORIGINAL: rhklenke ... I know of no ECU that will monitor the incoming pulses and filter them like an IPD receiver will, so the only way to get reliable shutdown on loss-of-signal is to use PCM. ... Bob regards Thomas Bob |
RE: PPM, PCM ?
Gents,
For me, the issue is'nt to do with PPM versus PCM. I have once experienced complete lockout: i.e. a situation where a perfectly working system suddenly appears to die and all further stick inputs are completely ignored. Only by switching the Tx off then back on brought things back to normal. Luckily this happened on the ground but I (stupidly!) continued with the day's flying - but happily with no further occurences. Having read about similar instances in this forum, I now know "lockout" can happen with some regularity. My setup was a PCM Futaba 149DP Rx and T9CP Tx. I've no hard evidence to suggest that any other system is better or worse, so I'm not going to switch on the basis of one occurence. PCM is definitely far less susceptible to interference - I, like many others on this forum no doubt, have first-hand experience of the improvements in control stability that PCM can offer. However, PCM is more complex and with increased complexity there is greater scope for errors/shortfalls in the design. There may be a case where the Tx or RX does not cater for an unforseen or unusual combination of circumstances or events. Thus when this situation occurs, the result could be a "lockout" condition where the electronics/software enters into an unkown and unrecoverable mode. For now, I'll continue with Futaba PCM - until I too have lost an expensive jet due to unknown causes!! Bob |
RE: PPM, PCM ?
PCM is definitely far less susceptible to interference Best regards, Enrique |
RE: PPM, PCM ?
ORIGINAL: dwayne_doberman For me, the issue is'nt to do with PPM versus PCM. I have once experienced complete lockout: i.e. a situation where a perfectly working system suddenly appears to die and all further stick inputs are completely ignored. Only by switching the Tx off then back on brought things back to normal. Best example I've seen of that is a club member who was using an old Futaba PPM TX. A few times he got himself in a situation where he was a bit "over his head", and then he crashed and blamed the radio. Of course everyone refused to believe him because he only crashed after getting himself confused / worried, and the radio always worked after the crash. Well, turns out he was actually right. We found out that when the radio was "squeezed" slightly it stopped transmitting and the LCD (showing the TX voltage etc) went blank; when pressure on the case was removed, it started working again. (The reason he crashed when he got "worked up" was that he was subconciously gripping the TX a bit harder.) Gordon |
RE: PPM, PCM ?
ORIGINAL: erbroens PCM is definitely far less susceptible to interference Best regards, Enrique Bob |
RE: PPM, PCM ?
Well I am a computer programmer, and I studied electrical engineering.. althought I never worked in telecommunications or never got much into it, I never found a satisfactory explanation about how a digital converter could be smarter to skip "errant edges" (PCM) than a well designed analogic filter receiver (PPM) ....
This is the kind of question that IMO has a "grey area" or not only just 1 and 0´s... and so unless someone has a solid explanation of it and real field experimentation data , statements like "PCM is better" are simply invalid. All I could said is the empirical testing that I have done myself in the last 25 years. flying jets, giant scale aircraft with gasoline engines and helicopters with PCM and PPM with the same grade of success on the quality of the radio link... I only prefer the PCM receivers because of the factory build feature of the failsafe. If the manufacturer would provide this feature in a PPM system, based in my experiences, I would buy it without bothering if it is PCM or PPM... Best regards, Enrique |
RE: PPM, PCM ?
Enrique,
To make it simple, PCM means Pulse Code Modulation. That means that a proprietary code is encapsulated in the frame sent by your TX. The receiver reads only frames with this code. Whatever is received without this 'password' is trashed. This way you filter better the signal and you increase the reception range as well. Yann |
RE: PPM, PCM ?
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RE: PPM, PCM ?
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RE: PPM, PCM ?
ORIGINAL: erbroens Well I am a computer programmer, and I studied electrical engineering.. althought I never worked in telecommunications or never got much into it, I never found a satisfactory explanation about how a digital converter could be smarter to skip "errant edges" (PCM) than a well designed analogic filter receiver (PPM) .... This is the kind of question that IMO has a "grey area" or not only just 1 and 0´s... and so unless someone has a solid explanation of it and real field experimentation data , statements like "PCM is better" are simply invalid. All I could said is the empirical testing that I have done myself in the last 25 years. flying jets, giant scale aircraft with gasoline engines and helicopters with PCM and PPM with the same grade of success on the quality of the radio link... I only prefer the PCM receivers because of the factory build feature of the failsafe. If the manufacturer would provide this feature in a PPM system, based in my experiences, I would buy it without bothering if it is PCM or PPM... Best regards, Enrique Bob [/quote] |
RE: PPM, PCM ?
Yann: thanks for the explanation of what PCM means... :)
Rhlenke: the grey area is how the current hardware processes this statistical probability.. pretty much like a pixelized edge of a blurred digital pic... as you know not all digital cameras have the same image quality, althought they share the basic digitalizing algorithm. They way how this data is processed can often lead to errors equal or greater than a non standarized data filter.(sorry if I didn´t used the correct english technical terms). About why I didn´t use Multiplex stuff is because it is not available as the Futaba... and anyway, why change for a brand that worked OK for me so many years? I had in my bench a PPM never crashed receiver that I flew a lot in a plane and I know that is 100% reliable. Instead of spending U$ 300 (yes, that´s the price of it here!) in another PCM receiver, I saved this money helping myself buying more and better acessories for my jets. Best regards, Enrique |
RE: PPM, PCM ?
ORIGINAL: erbroens Rhlenke: the grey area is how the current hardware processes this statistical probability.. pretty much like a pixelized edge of a blurred digital pic... as you know not all digital cameras have the same image quality, althought they share the basic digitalizing algorithm. They way how this data is processed can often lead to errors equal or greater than a non standarized data filter.(sorry if I didn´t used the correct english technical terms). Anyway, to each his own... Bob |
RE: PPM, PCM ?
Yes you are right . it really not fits at all, I just tried to explain it a way that most people who are not
information technology professionals or engineers could grasp the basic concept of the problem, nor to say that I am typing in a language that I learned mostly reading old model airplane magazines... and yes, to each is own. in this little planet there is no absolute truths or periods,, we are blessed to see and do things in infinite different ways. (of course some ways are more elegant and efficient than others) ;) Enrique |
RE: PPM, PCM ?
Enrique, which futaba PPM rx do you use ? the 138 DF ?
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RE: PPM, PCM ?
Hi
Okay talking as a profesional in the electronics industry. The reason that PCM is better than PPM can be explained with this simple analogy. You are in a crowded room with the a very loud band playing in the background. You are trying to hold a conversation with someone. Is it easier to follow a conversation that uses all different kinds of words ( eg analog) or simple yes or no ( digital) Obviously the simple yes or no win out, as even if you misinterpret one yes/no answer it will have a very small effect on the overall message. Where as get an entire word wrong in using full word example it will change the meaning of the entire sentence. If you want bored by the maths I can dig them out. As to the debate if PPM is better than PCM is in my opinion a no brainer. This belief that PPM will give you warning of a poor signal is frankly nuts. Unless it is very light and very short lived interference then you can kiss goodbye to your jet ten times over before a good well maintained PCM reciever decides to go into failsafe ( signal to noise ration several orders of magnitude higher than a PPM receiver could ever hope to cope with). I have flown PCM in helicopters and planes ( off all varieties) for several years with out any problems. To me use PCM there is no substitute. Mike currently building a sand bag wall for cover. |
RE: PPM, PCM ?
Mike, you are flat wrong. The stuff you said may apply to reular, un-post-processed PPM systems, but DEFINITELY NOT a system like the MPX IPD. IPD has fail safe protect just like PCM and it works very well. Harry C can tell us all the smallest of tech details, but he has not yet chimed in here. In fact much of what has been said here by the PCM proponents about PPM only applies to non-post-processed PPM.
I have flown Futaba and JR PCM. In my experience, the MPX IPD has been light years ahead, for me. I don't know if that is due to the IPD or the legendary high output of the MPX Profi TX. But frankly, it don't matter cause it has REALLY worked well! Ebroens, MPX makes the IPD RXs in + & - shift, so they should work with any PPM transmission. |
RE: PPM, PCM ?
Hi
I will respect your opinion and I know nothing about the Multiplex system however simple truth. if you can't get the signal through in the first place then you can post process to your hearts content it wont make a wit of difference. Mike |
RE: PPM, PCM ?
Harry C, we need you!
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RE: PPM, PCM ?
Wocketman: this feature is cool, + and - shift options allow the use of a Futaba or JR tx without restrictions. and like you said many experienced modelers around are happy using Inteligent Pulse
Decoding instead of PCM, the only problem (at least, for me) that MPX gear is not as easy to find as the most popular brands of radios around... Mike & rhklenke: perhaps we could be more productive discussing how we could create a way to test a PPM and a PCM receiver side by side, comparing the data and find some conclusions, instead of debating theory... perhaps a low power radio signal emissor or something like this. Best regards, Enrique |
RE: PPM, PCM ?
ORIGINAL: mikehannah ... if you can't get the signal through in the first place then you can post process to your hearts content it wont make a wit of difference. Mike Thomas |
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