Please let me know your source on this as this is completely at odds with
everything credible I have ever seen on PCM.
Even when the PCM is in failsafe, as soon as one good packet comes through
the servos are sent the good data. There is no waiting, no 'lockout'.
What looks like lockout is just a lack of good data getting through.
See if you can find that helicopter magazine article, I would like
to read it to see how they did their tests and what the results
were.
Another problem is that most pilots will have a hard time telling when
they have control and when they don't, in the environment of strong
interferance.
This means that some pilots will think that they are getting some effective
control through the glitching on a PPM and also think that it takes longer
to get control back on the PCM. The human observations are just not very good
for this sort of testing.
I still say PCM lockout is a myth just as the same of the myth of being able
to save a bird through the glitching on PPM. If the interferance is bad enough
to 'lockout' the PCM, you will have NO control on the PPM system either.
The problem is that it is very hard to do good simulation of the problem,
making it very hard to prove one way or the other.
The other problem is that legend, myth and advertizing hype are often
substituted for facts, especially in RC.
ALL RC radios have LOCKOUT, if the signal ain't getting through,
THE SIGNAL AIN'T GETTING THROUGH!
The question is, do you want the servos to be in a predictable position
or do you want them jumping around all over the place, perhaps even breaking
themselves by driving past their mechanical limits?
michael N6CHV AMA 77292
Jason Werner wrote:
>
> Michael,
> All PCM models have the lockout. Perhaps I did not explain it correctly
> and that is the problem.
>
> PCM works in 2 "stages". The first stage is the bad packet rejection.
> This occurs regularly as a bad packet or two goes through. These bad
> packets are generally too short to result in anything mroe than a packet
> rejection error. It jsut gets the next valid one and keeps moving.
> The second stage is when enough bad packets are recieved to cause the
> system to initiate the failsafe procedure. Most people will agree (and a
> helicopter magazine did a test on this) that once initiated, you will lose
> around a second of control once a valid packet is returned. This is
> inherent in the system's design, and to be honest is not a bad thing.
> The main time that this presents a problem is with reoccuring bad
> packets. Take 2 different situations that have similar results. For helis
> say your muffler bolt breaks and it starts vibrating. Normal results is a
> glitch. This could cause a crash yes, but normally the user can throttle
> down and the rf problem goes away. End result is that the user could get
> the heli down in one piece. With PCM you get a lock in which failsafe is
> initiated. Once initiated it takes about a second to regain full control.
> A second in a heli normally results in a crash.
> A soaring related problem can be loss of range. The PCM rx is designed
> to toss out bad packets. At long range, bad packets are more common. So
> eventually you will lose control of the plane. Even though good packets are
> still getting through, bad packets are as well so failsafe goes into effect.
> Plane flys away. With IPD the good packets still get processed though your
> control is lessened. But you at least have a chance to turn the plane back
> or track down the problem.
>
> IS PCM bad? NO WAY! It is fine. Most of the positives of PCM over PPM are
> true and good. But again, most are also not really needed. So it its up to
> you to decide.
>
> Jason Werner
>
> ----- Original Message -----
> From: "Michael Neverdosky" <[EMAIL PROTECTED]>
> To: "RCSE" <[EMAIL PROTECTED]>
> Sent: Thursday, July 13, 2000 12:56 PM
> Subject: Re: [RCSE] General sailplane radio: FM or PCM?
>
> > What system does this?
> >
> > I have a Futaba and Jr system and they do NOT LOCKOUT.
> > EVERY VALID FRAME of data results in an update to the servos.
> >
> > The only time delay is how long the receiver waits to go to the
> > preprogramed 'fail safe' position. On the JR this is 1/3, 1/2 or 1 second.
> > On the JR control is returned INSTANTLY when good info is received.
> >
> > Now as long as the interferance is so bad that no good data gets through
> > you have no control but that is true for EVERY system no matter what
> > fancy acronym you use.
> >
> > BTW I am willing to admit that *some* PCM systems might have a lockout
> > 'feature', but I have never seen one. I would be interested to hear
> > what systems are programmed this way?
> >
> > No one system is the answer to every possible interferance problem, at
> > least not in production for modlers, and not in a size and weight that
> > most of us would want to put into our planes.
> >
> > michael N6CHV AMA 77292
> >
> > Jason Werner wrote:
> >
> > > - And for the killer! The PCM lockout. When
> the
> > > PCM rx gets too many bad packets it then goes into a lockout or failsafe
> > > position. This continues for several refresh cycles after a valid
> packet is
> > > recieved. Most are around 1 second long before control is returned.
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