DeBunking Myths

[MicroHeli-Nut]

The myrths of PCM

http://jdgee.netfirms.com/pcm_ppm.html

"Case in point, a Raptor with 94357's on cyclic and throttle, a 94360 on collective and only one digital servo on the tail. Why do I need PCM? With 20 gallons through the bird I've never seen a glitch. My Freya with OS C-Spec flew its first 2 gallons on an FM RX, the only time I saw a glitch was on the tailgate of my truck in a soybean field in Huntsville Alabama and that was due to interference. The Caliber 30 I was flying on the same channel flew right through it and I didn't know that the interference was that bad otherwise I would have changed channels on it too. Which BTW, fixed the Freya.

The point is, unless you have the capability to measure the hits via the microprocessor decoder on the RX, if you fly PCM, you fly BLIND and security is ASSUMED. My stance on this issue is well documented from as far back as 2 years ago on RR and I still maintain it. Only the RX's that CY is flying has the capability to measure hits as well as the older Infinity 1000 RX's that I use for scanning purposes. In CY's case, Dave Youngblood tapped into the processor for the info and I'm sure they still use it because PCM hasn't changed and the spectrum we fly in is only more crowded now. A lot of the hits are from noise sources on the heli itself. Single conversion PCM JR receivers are even more susceptible to interference than the Dual conversion RX's everyone else uses. ABC&W is a marketing illusion "


Are You confused? I know i'm not only confused after reading this, but also very troubled, because this means i'm grounded again wifout a receiver that i can use.

[baby_zyklon]

it is very very confusing...so according to the author, is ppm better or pcm better? To me, pcm seems to be better, at least you don't get any glitch, kicking into failsafe with low throttle and crashing is definately better than going around at hover speed and not knowing when do you not have 100% control, isn't it? IMHO, there really is no need for us to know how many beat or signal our rx miss, because end of the day, we only want to take off and land in one piece without losing control during the flight, isn't it?

And this statement a bit the....

"Do you know if the RX goes into hold for even an instance? Hold states are kept in processor memory until you switch off."

Actually I will know that rx go into hold for even an instance, coz if you set your fs throttle to low, when the throttle goes down without you asking it to, then you should know failsafe already mah...unless our defination of hold is different...also, fs doesn't kick in immediately, thought is only like 3/4 of sec after you lose signal, coz I am sure you all know loh, when you switch off the tx before the rx, there will be a time split between switching off the tx and fs coming in, like lag...fs holding at low throttle and the heli coming down is better than glitch and then go "jump" around high throttle and losing the model, or worse still, bang into someone else, bu shi mah?

[PhiBeR]

Ah.. the article makes sense to me..
Gracias to my school work.. hahaha..
But this is one of my hate modules, signal processing!

SINGLE CONVERSION VS. DUAL CONVERSION RECEIVERS

HAhaha.. here's one more link to blur u guys..
Ray, dun fly liao la, ur Electron 6 is not as good as u think!

Anyway. after reading thru the article on PCM vc PPM, i guess
i wun really spend the extra moola to get a PCM receiver!
Esp on a micro-heli, coz using a PCM RX with non-digital servos
is total waste of money.
The normal analog srevos wun be able to decode teh extra information
from a PCM RX anyway.. So why waste the money?

BZ,

In PCM system, it's not you don't get any glitches,
but it's that the PCM system will mask all glitches by rejecting
invalid frames (glitches) and keeping the servos at last known
good position. So with PCM system, u won't be able to notice any
glitches until the glitches are so bad that the RX goes into failsafe
or "hold" mode used in the article.

The whole article doesn't address the pros n cons of the PCM vs
PPM RXs, it rather focuses more on how PPM and PCM decodes the
frames sent by the TX.

In conclusion to the whole article, there is no range advantage of
PCM over PPM. There is no glitch advantage of PCM over PPM.
in PCM u get glitches, but its masked by the nature of the system.
So if there are glitches, u wun know becoz the TX will retransmit
the frames.
Why does PCM seemed "glitch-free"? becoz PCM is capable of
sending more bits per channel (10bits vs 1 pulse) cf. PPM.
Thus, the correct frame is resent fast enough to replace the
rejected frame. Resulting in a "glitch-free" operation.
This gives rise to a very big disadvantage, intermittent glitches due
to inteferences or technical errors will not be noticed by a PCM RX
until to the point when the error is so bad that ur model will go into
failsafe. Then u know it's time for a crash (or spectacular crash) as
the articale puts it.

PCM RXs will however "display" the Transmissino glitch in terms
of the usual "Servo glitching" and anyone with sufficient RC experience
will know that it's time to bring the model back to prevent any mishaps!

So the only pro of PCM mentioned in the article is failsafe programming
which allows u to set the failsafe programming options on the TX
and is sent to the RX to use when the RX goes into hold mode..
For a PPM receiver, that is not possible and "failsafe" in PPM RXs
usually means the PPM receiver will hold the signal at the "last
known good" frame.. ala Berg 6 g3 i believe..


Juz my 50cents worth of interpreting the article!!

[MicroHeli-Nut]

My current Options:

1) Alpha 835 Schulze Receiver -> DSP Technology + Glitch Counter (Same as Berg 6) $150 ?

2) CRX-M7 -> DSP technology $90

3) JR micro 610 PPM or JR 770 PPM -> $120 -$140

4) hitec Electron 6 -> Dual COn -> $76

5) Sanwa PCM 7Channel -> $140....

[fuse]

eletron 6 does glitch!!!

pcm is the way to go...

[MicroHeli-Nut]

Here, price is not an issue liao, as long as the receiver offers a certain degree of CREDIBLE protection.......

Anyone try SanWa PCM receivers before?