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FM vs PCM

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Old 04-14-2002, 01:55 PM
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crashdaily
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Default FM vs PCM

I posted this question on the old forum but would like more input:


Does PCM offer a more stable link to the reciver than FM in a gasoline powered aircraft? what's your opinion?
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Old 04-14-2002, 06:41 PM
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the range check worked out fine, with engine on/ off, smoke on/off everything worked just fine, it flew quite well, other planes fly well (no interferance) I've heard conflicting opinions about
PCM vs FM. personally I'd sooner install a flight stabilization unit (futaba makes one) before I'd go with a fail safe since my plane is NEVER in the same position and attitude, how can you program fail safe if you don't know what position your plane will be in when it takes a hit? I feel the problem is not in my transmitter as this was a very weird situation.

The last flight was fine I flew my 7 foot span plane to a spec and back many times but within 200 yards of me it stopped responding. it only took about 3 seconds for it to turn into a pile of trash. It's hard to say after the fact but I'm thinking that maybe my switch harness was defective since there was very little detent betwen on/off. I figure since I am replacing the plane that i would get other opinions on the subject of FM vs PCM.
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Old 04-15-2002, 01:55 PM
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Default FM vs PCM

The only possible use (as far as I can see.... maybe) is for choppers....maybe. i thank you all for your input. I was considering going PCM because that's what others at the field told me but with what I've learned from you has helped me make a somewhat educated decision.... which actually is the same as my un-educated decision..... ppm. everything worked fine.... not a single glicht. while building I did everything possible to isolate the reciever..... reciever was mounted as far as practically possible from everything else and every power cable was twisted to reduce emf's. I truly feel that the failure was due to a faulty switch, even though all three switches were knocked apart the switch for the reciever had very little detent left as compared to the other two.


Thank You.
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Old 04-16-2002, 09:05 PM
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Default fail safe

Now there's something I never considered.... failsafe into a snap-roll.... excellent idea, but on the flip side I'd really be upset if my plane went into a snap and I regained controll just in time to flare into the ground..... I believe I'm going to stick with ppm if for no other reason...K.I.S.S. I'd rather see my servos glitching on the ground and decide not to fly vs. last position hold and find out later.... when it's already in the air. in my opionion if the reciever is going to mask the hits I'd like to know about it. glitching for example, would be a good sign.
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Old 04-17-2002, 04:36 PM
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Default PPM, PCM, ATM, STP

When I bought my radios.....I did not know anything about this stuff, and still don't......
I turn my TX on....My rx responds.
No runs, NO HITS, no errors.
Good Luck

DOC
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Old 04-17-2002, 08:28 PM
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Default FM vs PCM

ok, we got it straightened out that what we all normally refer to as FM is really ppm. I read everyones opinions and I'm starting to like the idea of pcm. just to set the record straight I started flying by myself out in the backfilled strip mines in Pennsylvania. fail safe meant "saving my plane" because there was no one around for miles and it would be virtually impossible for my planes to get away due to hills and trees (realy, the trees have big hands!!). I grew up there and at the risk of being politically INcorrect, safety was never at the top of my list, BUT.... since I moved to Las Vegas and fly "in town" I'm very paranoid about what my plane is doing, where it's pointed and where it would go if I lost it. it seems to fill my mind the entire time I'm flying, but that's the price you pay to live where it dosn't rain or snow

"saving my plane" is why I never bothered with pcm, but knowing that failsafe would (as I just explained to the woman) make my plane fall from the sky instead of fly into traffic is a very good selling point for me, I'm changing my mind and I'm going PCM.

I would also like to clear up the notion that I had interference problems.... until this crash, I've never lost control of any of my planes, my zagi flys great (when it's not busted) my magic flys great, and all the others....all on the same JR 642 on ppm. this was a very isolated situation which I'm 90% sure was a switch failure, but since I'm replacing my quarter scale airtrax with another one(which wasn't easy to find) I want to take whatever precautions I can afford to keep this plane longer than a weekend.
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Old 05-13-2002, 05:54 PM
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Default reliability

Ok, I've been watching and reading the posts and the last 3 or 4 seem to be missing a point about pcm.... it may NOt be hiding your problems but actually curing them thru reliablity enhancement. if you look back a couple of posts you'll see that pcm sends a "box" of information per channel AND it sends not one but two boxes in a row, just in case the first one is interferred with it may be that simple. one thing you might consider as far as glitching..... I'm not a heli guy and I'm not up to speed on gyro's but if the still have a spinning disk of any kind inside yet, well this may be a source of static. if nothing else try your glitching chopper without the gyro running. I've had an occurance where I had My dazzeler in one hand and the transmitter in the other and while walking thru the field I found a spot about twenty feet in diam. that glitched the hell out of the plane. I could step one step out of the area and nothing... one step back.... epileptic plane... who knows.
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Old 05-15-2002, 05:54 PM
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Default FM vs PCM

Thank You Harry,


You've just stated what I was trying to say about pcm being more reliable than ppm. even though they booth will take the same hit pcm is better at handling the situation remeber the part about pcm sending 2 Boxes of information per channel? vs ppm.
PCM dosen't get rid of interference but deals with it much better....ie an enhancement to ppm. yes it hides the interference but if it isn't affecting your flying or range checking as it would in ppm then what's the problem? Really that's what it really comes down to isn't it? PCM dosen't glitch like ppm, that alone is a major improvement, what happens when you take say a 2 second hit on ppm? the servos glitch well past there intended limits causing the aircraft to become uncontrollable . PCM has a "last good signal hold" until it recieves another or goes into fail safe. suppose your in a low inverted pass when this happens.... ppm is into the ground for sure. PCM will continue on with the last good input(provided you don't go into fail safe) until it recieves another good signal. Face it.... PCM IS better technology. stop defending PPM like you invented it already.
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