Thread: FM or PCM??
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Old 02-12-2004, 12:45 PM
  #21  
tadawson
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Join Date: Sep 2002
Location: Lewisville, TX
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Default RE: FM or PCM??

But, with IPD, the systen will have a hell of a lot harder time figuring out what a bad frame is, versus PCM. On IPD, any signal which has servo position data is the realm of reality (the normal range of pulse times) will be accepted, valid or not. With PCM, the checksum makes a much more distinct go/no-go decision on a frame possible. Perhaps the net effect is the same - there can't be too many cases where a bad signal still looks good (but in error) to a receiver. Everyone seems to be ignoring the inherently greater S/N ration of PCM (greater usable range) and I don't know about you guys, but having to set failsafes at the RX would piss me off royally! I have some planes/helis that the receivers are buried in pretty deep, and if I am trying to setup a failsafe to behave a certain way, taking the *#&Y$()*# thing apart every time I need to make a tweak would just plain suck! IPD sounds like a very viable option, but I would position it between "traditional" PPM and PCM. I don't think it can (or will) ever be able to totally equal PCM, but if they get 90% of the way there for, say, 50% of the cost, it sure will sell! As much as I have been attacted to the Evo line, the lack of PCM is really a great deterrent to me, since I just plain refuse to fly my helis on anything BUT PCM. (Yes, I have flown PPM in the past, and promptly moved up - the interference handling of PPM (or lack thereof) STANK! And for those who say you can't feel interferecnce in PCM, you apparently are not trying hard enough - to
me, it is obvious, far before taking a lockout, which will most likely be INTERMITTENT and recoverable. I think too many folks mistake the LOCK in lockout to mean that once you go there, that it will stay locked. In a heli, where there is a lot of potential for on-board generated RF noise (bad bearings, etc.) a lockout will drop the throttle, thus (frequently) removing the source of noise, allowing you to try to keep flying, or to auto the bird safely.

- Tim