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Old Mar 26, 2002, 08:38 PM
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Bellmore, New York,USA
Joined Jul 2001
112 Posts
Z-PCM vs S-PCM

Hi all,
I've been going through the back posts reading the various opinions on the debate of PPM vs PCM. I now want to buy PCM receivers for my Eco's. I was going thru my JR manual, I have the XP652, they mention 2 types of PCM. They list the Z-PCM and S-PCM. I have followed some links to websites that attempt to explain the difference between them. I am confused. Can anyone give me the abridged version? Do I need to even care which one to use? It would seem by the manual that the Fail-safe features are the same for either one. What are the majority of PCM fliers using, or is this a brand type of thing?

Thanks,

Mike
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Old Mar 26, 2002, 08:52 PM
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Santa Rosa, Northern CA, USA
Joined Oct 1999
2,472 Posts
Mike,

Pretty sure JR S PCM is higher resolution than the older Z PCM (1024 vs maybe 511?)

Does it matter, I don't think it does very much. The servos should follow the sticks and trim a little tighter with S PCM, but with an ECO I doubt you would notice. If you are using the latest big bucks super servos, then maybe, but most smaller servos and linkage have more "slop" than the PCM mode.

Hope this helps,
Dave

PS: How long are you going to set the delay on your fail-safe?

Shorter the better in my book...
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Old Mar 26, 2002, 09:12 PM
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Bellmore, New York,USA
Joined Jul 2001
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Hi Dave,
I haven't given the setup much thought as yet. I wanted to sort out this other issue first. I guess I'd cut the motor to prevent a flyaway and perhaps set the swashplate servo's to some neutral setting. The radio offers 3 delay settings, .3, .5 and 1 sec. What settings do you guys use and I guess the question still stands, which type is the current prefered type and why?

Mike
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Old Mar 26, 2002, 09:14 PM
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United States, FL, West Palm Beach
Joined Jun 2001
2,216 Posts
Hello

ZPCM is 512(half that of the SPCM).

I use a 910xz PCM reciever(10 ch--overkill but came with my JR10sx radio--ebay special) in my Eco 8. The reciever is preforming flawlessly. To me PCM is the way to go, I don't want any glitching for any reason to happen when Im flying.

I disabled my fail safe.

Carlo
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Old Mar 26, 2002, 09:42 PM
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Lake Louise, AB, Canada
Joined Feb 2000
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AFAIK, there is no time adjustment avialable with SPCM, the newer PCM system.

I have the failsafe on my LOGO 20 set this way:
- almost zero throttle (want the heli to come down right away, but don't want slow start if it's a momentary glitch).
-neutral cyclic
-slightly negative pitch

Cheers!

Glen
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Old Mar 26, 2002, 11:32 PM
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Irvine, CA, USA
Joined Oct 2000
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Back in my plank days, I had both the Futaba PCM 512 and 1024 receivers. With the same servos on same plane, the PCM512 feels a bit sluggish compared to 1024.

Glen you brought up a good point on the near zero throttle failsafe. Right now I got mine set to zero throttle and neutral cyclic and 2 degrees pitch because I want to to "float down" when it locks up. But like you said, I wouldn't want my ESC to go through 15 secs spinup cycle after momentary glitch. I'll have to experiment with what the lowest throttle setting I can go before shutting down. Thanks for the great advice.
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Old Mar 27, 2002, 05:04 AM
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Lake Louise, AB, Canada
Joined Feb 2000
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Hello Stephen,

My first LOGO 20 had frequent failsafe events, say once every 20 flights or so. The seemed to last for over 5 seconds, and the heli would rear up from FF flight, hesitate, and start to descend, which was a good thing. At one point I noticed that I seemed to have control of the cyclic, at least near the end of the event! Then I figured out that what I was experiencing was a half-second glitch followed by a 5 second (at least) slow start - DOH!

The reason I went to slightly negative pitch was that I wanted the blades to still be turning after say, a few seconds to enable a recovery if that should ever happen.

Glen
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Old Mar 27, 2002, 10:53 PM
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Bellmore, New York,USA
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Thanks guys for the input. I had hoped for a few more replys but at least I now have some info to start with. If I understand things correctly the S-PCM receiver with 1024 bits resolution would be the better choice. As far as the failsafe settings I understand the reasoning for the throttle not being set to 0 to avoid a long slow start condition. As far as the pitch goes I need to think about that one a bit. Negative pitch will help build energy in the rotors but if I'm going in with no control then what good is energy I can't take advantage of. On the other hand if I have a some positive pitch it may slow the decent a little bit and possibly keep the damage down. With a quick recovery in flight it seems niether way has any advantage. I'm still hoping a few more folks will add their thoughts.

Mike
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Old Mar 27, 2002, 11:43 PM
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Sorry, Just me again

This thread has some very good points so far.

Steph mentions Plank days. I wonder what Plank and servos, were they fast powerfull hi-res digital servos? Does this also apply to an ECO?

Eco8gator says "I disabled my fail safe." Yikes, so much for failsafe. He also caught my 511 vs 512. That missing bit is the glitch that FM tends to warn you about with a quick shiver.

So what does failsafe really do for you? If your BEC or RX batt dies, nothing. If you get an RF "bounce" then it will keep the Heli from jumping. If you have an issue with the basic set up as in noise on the Heli creating problems, it will mask it, till maybe it is to late.

But, if you get someone else turning on, same freq as you, then it will go to preset and wait (forever). I like the idea of slowing the Heli down in this situation.

Happy Landings,
Dave

PS: I like failsafe with planes that have Flaps, better yet Crow, as it can turn the motor off and slow the plane down. Also, like the idea that the motor will not jump to life due to a glitch. This can be a real problem when you are not ready for it.
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Old Mar 28, 2002, 08:08 PM
If I aint flyin, I'm Dyin
Hermitage Tn.
Joined Mar 2002
44 Posts
My experience with the 512 over the 1024 has nothing to do with the resolution of the servos or the input from the radio. It is the size of the error correction signal that it is sent to the receiver. The signal gets put into a data stream with a redundant algorithum. The redundant algorithum then get decoded for errors if an error is recieved the glitch is then ignored. I may be wrong but this is how I understand the system to work.

Me personally I wouldnt put a PCM receiver in an ECO 8. I always used the mini JR 610m with excellent results.
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Old Mar 28, 2002, 09:21 PM
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Bellmore, New York,USA
Joined Jul 2001
112 Posts
preditor4u,
The reason I'm want to put one into my Eco is that I'm getting ready to order a Logo 16 or a 20, I haven't decided yet. I'm waiting for Uncle Sam to send me some money he ows me. I'll be going to more cells, more power and more dollars in the sky at any one time. I am currently building a switching regulator BEC which I will test in my brushless Eco prior to using it in the Logo. I just want to get a feel for how it is going to work. I prefer to be carefull. I also posted the question to try and get an understanding of the differences between the 2 type. I do appreciate the answers given so far.

Mike
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