PCM&PPM Whats the difference

[rotorwrecker]

Hi everyone.So theres PCM and PPM what is the difference,What does it mean.

Dave.

[unwind-protect]

Hopefully this explains it quite thoroughly; if not, it needs to be changed so it does!:

Radio protocols - RC Helicopter Wiki

[pchristy]

PPM is the original "digital" system as pioneered by Don Mathes and Doug Spreng back in the early 60's. It was designed to overcome the lag and drift problems that plagued analogue proportional systems back then. It provides very rapid (almost instantaneous) response and good accuracy, but is susceptible to interference, and its response to interference or signal loss is unpredictable.

PCM encodes the signal into a stream of binary numbers, which the receiver decodes back into PPM to maintain compatibility with servos. It is much more resistant to interference, and is much more predictable when it loses the signal. It can be programmed to "fail-safe" if the signal is lost. On the down side, the latency is much higher (the lag between moving the stick and the servo responding), and this gets worse the more channels you have and the more bits you use. However the more bits you use, the more accurate the servos get, so a compromise has to be reached somewhere!

PCM is almost essential on all but the smallest electric machines, due to the copious amounts of electrical noise around!

[rotorwrecker]

Hopefully this explains it quite thoroughly; if not, it needs to be changed so it does!:

Radio protocols - RC Helicopter Wiki

Thanks for that link.Lots of info there and try to understand but very interesting.

Dave.

[rotorwrecker]

PPM is the original "digital" system as pioneered by Don Mathes and Doug Spreng back in the early 60's. It was designed to overcome the lag and drift problems that plagued analogue proportional systems back then. It provides very rapid (almost instantaneous) response and good accuracy, but is susceptible to interference, and its response to interference or signal loss is unpredictable.

PCM encodes the signal into a stream of binary numbers, which the receiver decodes back into PPM to maintain compatibility with servos. It is much more resistant to interference, and is much more predictable when it loses the signal. It can be programmed to "fail-safe" if the signal is lost. On the down side, the latency is much higher (the lag between moving the stick and the servo responding), and this gets worse the more channels you have and the more bits you use. However the more bits you use, the more accurate the servos get, so a compromise has to be reached somewhere!

PCM is almost essential on all but the smallest electric machines, due to the copious amounts of electrical noise around!

Hi thanks for the info.You have given it in a way which a can understand as i read and not over complicated.Point is i think i now understand so now know the pros and cons of the different types.I bought a used futaba pcm reciever off a member to go my mates kalt baron and we have only ever used ppm but his futaba C7 book says it can handle either so thats good.

Dave.

[trillian]

At the risk of complicating matters further, there were a few different schemes devised in both PPM and PCM to maintain a signal and avoid interference. The highest risk of noise issues comes from small electric helis because of the electric motor and the close proximity of everything.

People flew nitro helis for many years on 35mhz (and still do).

By the way, what model Baron is it?

[rotorwrecker]

Hi.Its a Kalt baron 30 which he bought off a nissan forum.Its like new with an irvine 36 engine.The only things missing are battery pack,rx and gyro and he asked me if he should buy it when i was at his house.I thought the guy had made a mistake but it was right £45 posted I know parts are getting hard to find for it but they are out there.

Dave.

[trillian]

Yeah the Baron 30 was one of the later models and parts are not as difficult to find as some older machines. I usually see them go for around £100.00 so 45.00 is very cheap.

I have one as well and it is in nearly new condition but I don't know if I'll keep it because I am mainly interested in restoring some older Kalts and I have too many helis anyway.

It's definitely not a museum piece and there's no reason not to fly it really. It is a bit more fragile than something like a Raptor because of the shaft driven tail and the kinda funky way the collective works with the hollow main shaft.