Notices
RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

FM or PCM??

Old 02-14-2004, 10:35 PM
  #51  
PropAce
Member
 
Join Date: Feb 2004
Location: Phoenix, AZ
Posts: 61
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

It can easily be said that PCM is needed if you want glitches to not affect your flying performance and that the only thing that detirmins that the plane is flying on PCM is the receiver. Now can you gyes stop this needless argument on PCM and PPM if you have a big plane get PCM to keep it safe.[8D]
Old 02-14-2004, 11:52 PM
  #52  
Lynx
Senior Member
 
Join Date: Sep 2002
Location: Rochester, NY
Posts: 1,373
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

PCM glitches will show up as a no-responce as opposed to an unwanted responce on a PPM system. No matter what you do, they'll still show up. If you notice them, that's another story. Any number of tricks can be done to hide your perception of those errors. Then again to the average RC user, they'd perceive PCM as being better, even though it's not. Because the average RC user can't perceive a PCM frame drop, and the average user CAN perceive the average PPM frame error. Just ***** at servo manufactors, a simple 3 point servo signal buffer could be introduced to eliminate something like 50% or more of all errors on a PPM system with an absurdly small delay (1ms or less) This cost is PENNIES per servo.
Old 02-15-2004, 02:14 AM
  #53  
john 8750
Senior Member
 
john 8750's Avatar
 
Join Date: Jan 2003
Location: VAN NUYS, CA,
Posts: 388
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

I think that most who dont like PCM are only reacting to the higher price. This has been the case since we first had the PCM. I have four PCM's and they are superior to any other system to date.
Old 02-15-2004, 05:59 AM
  #54  
HarryC
My Feedback: (1)
 
Join Date: Feb 2002
Location: private, UNITED KINGDOM
Posts: 3,637
Likes: 0
Received 11 Likes on 7 Posts
Default RE: RE: FM or PCM??

PropAce and John Smith -

So you have actually tried IPD and DSR and found that they are not as good as PCM? Well done to you for keeping an open mind and conducting real trials before making your announcements. Or, as I suspect, you were not even aware of their existence or what they do or how they work but nevertheless you just pronounce PCM to be superior to all the other systems whose existence you don't even know of let alone actually try for yourself.

H
Old 02-15-2004, 06:29 AM
  #55  
HarryC
My Feedback: (1)
 
Join Date: Feb 2002
Location: private, UNITED KINGDOM
Posts: 3,637
Likes: 0
Received 11 Likes on 7 Posts
Default RE: RE: FM or PCM??

ORIGINAL: mglavin
I have observed the EVO and IPD RX operate at 5-6usec, this appeared to be the minimum pulse width or resolution at the RX I could note.
Michael, I suspect that what you were measuring was the size of the trim step at default travel values, not the resolution. My Evo sending to an IPD12 and measured at the servo sockets is incrementing the counter by 1us at a time.

If you set trim step to its lowest value of 0.5%, with control travel at 100% and servo travel at 100%, then the timing range from Mpx is 1100us so each trim step is 5.5us, which would account for your observation of 5-6us. Turn the control travel down to 1% and if necessary turn down the servo travel on that channel too so that you get 0.5% of a much smaller range, then use the trims and the counter will increment in steps of 1us.

I measured the jitter caused by my thumb on the stick at standard travel values. Pushing the stick forward was extremely steady, I was holding to within +/- 1us with low frequency of jitter, which surprised me. But pulling the stick back is quite different, there the thumb is not under compression and the timing jittered typically by up to 8 or 9us, very occasionally 10us, at quite high frequency. So the amplitude and frequency of the jitter caused by your muscles depends on whether you are pushing or pulling the stick.

H
Old 02-15-2004, 10:51 AM
  #56  
PropAce
Member
 
Join Date: Feb 2004
Location: Phoenix, AZ
Posts: 61
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

IDP and DSR never heard of thoes i just got a Futaba 7CAF and put it in my new sig extra with a load of high torq servos and have never had a problem im just saying that you gyes are overreacting about this the fact is that PPM is better cause if you get a very serious problem PCM wont let you know untill its so serious that the planes going down.
Old 02-15-2004, 11:02 AM
  #57  
Forgues Research
Senior Member
My Feedback: (7)
 
Forgues Research's Avatar
 
Join Date: Dec 2001
Location: Glen Robertson, ON, CANADA
Posts: 3,453
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

ORIGINAL: PropAce

IDP and DSR never heard of thoes i .
Old 02-15-2004, 05:11 PM
  #58  
HarryC
My Feedback: (1)
 
Join Date: Feb 2002
Location: private, UNITED KINGDOM
Posts: 3,637
Likes: 0
Received 11 Likes on 7 Posts
Default RE: RE: FM or PCM??

ORIGINAL: PropAce
the fact is that PPM is better cause if you get a very serious problem PCM wont let you know untill its so serious that the planes going down.
Propace, you are (unwittingly) making my point for me! What you have stated makes some assumptions which are true in common language but are technically false.

PPM and PCM are merely a code system to turn a pot voltage into a signal. Neither contains failsafe. PCM code alone sent to an Rx will cause jumping about as much as PPM does when interference strikes. There is nothing inherent in PCM that makes it failsafe. Failsafe is a totally separate system. It so happens that 20 odd years ago it was far easier to fit error detection and hence a failsafe system to digital data than to analogue data with the result that all PCM systems had failsafe included by default. This has led many people to confuse PCM and failsafe as being the same inseperable thing, and that therefore the failsafe behaviour is exclusive to PCM. But failsafe can now be fitted to PPM equipment and so to the user it appears to behave like PCM failsafe. It does not jump around or glitch when interference is present.

So look again at your statement in the light of that. My PPM radio does not show interference until it goes into failsafe, so it masks problems and won't let me know about trouble, just like PCM. On the other hand, if we disable the error checking of the failsafe part in a PCM Rx it will behave like PPM. So the failsafe behaviour and masking of problems is not inherent in PCM or excluded from PPM. The choice is between failsafe and non-failsafe systems rather than between PPM and PCM. All PCM sets include failsafe, PPM users have a choice.

H
Old 02-15-2004, 05:33 PM
  #59  
PropAce
Member
 
Join Date: Feb 2004
Location: Phoenix, AZ
Posts: 61
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

All i have to say about this harry is that i have used PPM for the 2 years i have been flying and im 17 so dont expect me to be an ace at thees technical issues you say im wrong about, it it works and causes me not problem i dont care. i have used PPM for 2 years and never had a crash and have never had a glitch. i have seen them but they were all on JR systems so thats why i trust Futaba with my plane and their new PPM 7 CHP. PCM covers up glitches if they happen.
Old 02-17-2004, 12:44 AM
  #60  
RTK
My Feedback: (1)
 
RTK's Avatar
 
Join Date: Apr 2003
Location: Left Coast , CA
Posts: 4,890
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

Hi Harry- Where do you set your failsafe on your system rx of tx?
Old 02-17-2004, 03:42 AM
  #61  
HarryC
My Feedback: (1)
 
Join Date: Feb 2002
Location: private, UNITED KINGDOM
Posts: 3,637
Likes: 0
Received 11 Likes on 7 Posts
Default RE: RE: FM or PCM??

The programming is done directly on the Rx, so it is independent of the type of Tx that is used and works with all brands in PPM mode.

H
Old 02-17-2004, 07:23 PM
  #62  
Lynx
Senior Member
 
Join Date: Sep 2002
Location: Rochester, NY
Posts: 1,373
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

Failsafe is always on the RX, it's totally useless to have it on the xmitter, because you're trying to provide signals when the xmitter can't be found.
Old 02-17-2004, 10:09 PM
  #63  
tadawson
Senior Member
 
Join Date: Sep 2002
Location: Lewisville, TX
Posts: 669
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: FM or PCM??

Lynx - ah, no, false! Failsafe is activated on the RX, but bloody well need not be programmed from there. On the JR and Futaba PCM radios, the failsafe settings are programmed on the transmitter, and sent to the RX via the RF link. If the signal is lost, the RX goes to the set of values received. The nice thing about this is that you can change RX and not have to reprogram it (or forget to . . .) or tune the failsafe parameters without either a) an external button you can bump and botch the settings or 2) having to take the #U#$# #$# aircraft apart if/when you need to make a change. Granted, they don't change much, but personally, I view programming at the RX a large downgrade. Cheaper, yeah, but like the old adage goes:

Good, Fast, Cheap - Pick any two!

- Tim
Old 02-18-2004, 03:15 AM
  #64  
Lynx
Senior Member
 
Join Date: Sep 2002
Location: Rochester, NY
Posts: 1,373
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: RE: FM or PCM??

What is everyone looking for any microscopic 'error' to attack the next person on? The threads seem like it here... I never said anything about programming method. The failsafe itself is on the RX. You can send the information on how to set up that failsafe any way you want. DSC, or a sub-channel programmed into the PCM xmitter or however, doesn't matter. The failsafe itself, exists inviolate of anything else on the receiver.
Old 02-18-2004, 12:51 PM
  #65  
tadawson
Senior Member
 
Join Date: Sep 2002
Location: Lewisville, TX
Posts: 669
Likes: 0
Received 0 Likes on 0 Posts
Default RE: RE: RE: FM or PCM??

I really wasn't trying to nitpick, but I frankly found no other way to read your comment. There is enough mis-information on this topic out there, that I just wanted to make sure that it was clear to all.

- Tim
Old 03-18-2004, 06:23 PM
  #66  
robkaiser
Junior Member
 
Join Date: Feb 2004
Location: Calgary, AB, CANADA
Posts: 1
Likes: 0
Received 0 Likes on 0 Posts
Default RE: FM or PCM??

I have to smile. Has anything in this thread helped the poor rookie with his original question?!

I am new to the sport as well, and am wrestling with the same issue. A shop in my neck of the woods has a sale on an FM 6102 e/w 4 servos for $299. I am sorely tempted by this price, but this thread has served to do very little but confuse me more.

Thanx for the effort all, but I think I'll just have to go with my gut!
Old 03-18-2004, 07:55 PM
  #67  
AMA-69405
Senior Member
My Feedback: (22)
 
AMA-69405's Avatar
 
Join Date: Nov 2002
Location: Dexter, KS
Posts: 192
Likes: 0
Received 0 Likes on 0 Posts
Default RE: FM or PCM??

Rob,

I'll repeat (in fact, I'll quote!) what I said early in this thread... post #6 to be exact... I still think this sums it up:

Tony,

Admittedly ad copy, I think the following quote from a well known distributor of RC equipment says it best:

"And as far as the tired old PCM vs. FM debate goes, do any of us really believe every TOC competitor in recent memory flew with PCM just to be fashionable?"

Despite the naysayers, the best fliers in the world seem to think there are advantages to flying PCM. In your specific case (the 6102 system and R700 PPM vs R770 PCM), there is exactly 20 bucks difference. IMHO, it's a no-brainer... buy the PCM receiver.
Gary L.
Old 03-18-2004, 11:59 PM
  #68  
aviti
My Feedback: (54)
 
Join Date: Dec 2002
Location: Ballwin, MO
Posts: 701
Likes: 0
Received 0 Likes on 0 Posts
Default RE: FM or PCM??

I've been reading these debates for years. The beginners are right, its just plain confusing and you don't know who to trust. I started flying on AM in 1981. Then I switched to PPM in 1984 and I saw less glitching when I rubbed metal to metal near my receiver. But I could still see some glitchs when I hooked a glow plug connecter up as I fiddled to get it locked on. A few years ago I decided to give PCM a try. Now I see no glitching when I had "metal" or electrical noise. Also, with digital servos, PPM receivers make them chatter, PCM does not.

I'm not looking for an explaination, I'm just saying that I am more confident that if there is a source of RF noise, PCM will be better. There's gotta be a reason that PCM can better handle a gas ignition system than PPM. I don't think a guy can go wrong with PCM. I'm sure another engineer type will dispute all this with 50 theories, but I've gotta say, the only planes I've crashed were due to finger glitches, not PCM glitches.....
Old 03-19-2004, 08:16 AM
  #69  
Forgues Research
Senior Member
My Feedback: (7)
 
Forgues Research's Avatar
 
Join Date: Dec 2001
Location: Glen Robertson, ON, CANADA
Posts: 3,453
Likes: 0
Received 0 Likes on 0 Posts
Default RE: FM or PCM??

ORIGINAL: aviti

I've been reading these debates for years. The beginners are right, its just plain confusing and you don't know who to trust. I started flying on AM in 1981. Then I switched to PPM in 1984 and I saw less glitching when I rubbed metal to metal near my receiver. But I could still see some glitchs when I hooked a glow plug connecter up as I fiddled to get it locked on. A few years ago I decided to give PCM a try. Now I see no glitching when I had "metal" or electrical noise. Also, with digital servos, PPM receivers make them chatter, PCM does not.

I'm not looking for an explaination, I'm just saying that I am more confident that if there is a source of RF noise, PCM will be better. There's gotta be a reason that PCM can better handle a gas ignition system than PPM. I don't think a guy can go wrong with PCM. I'm sure another engineer type will dispute all this with 50 theories, but I've gotta say, the only planes I've crashed were due to finger glitches, not PCM glitches.....
Your right, it will go on for a long time still, but Multiplex, which is about the best radio system on the planet, decided to stop making the PCM system, I beleive they might know something that even TOC pilots don't know. FMA FMS receivers (PPM ) do not jitter neither.

Roger

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.