[NSRCA-discussion] RX choices

[John Pavlick]

Ahh. Now I understand. Yeah, that's really what you're trying to do. Not
de-sensitize a servo that's too responsive, but rather make the most out of
the stick movement so that you can control it effectively. I get it now.
Thanks!

John Pavlick
http://www.idseng.com


> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org
> [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of J.Oddino
> Sent: Friday, September 15, 2006 1:58 PM
> To: NSRCA Mailing List
> Subject: Re: [NSRCA-discussion] RX choices
>
>
> John;
>
> A servo cannot be fast enough by definition.  Ideally it would follow the
> transmitter stick position with no delay (and no overshoot).  Servos are
> sometimes tested by inserting a sine wave signal at the input and
> measuring
> the amplitude and phase delay at the output.  At very low frequency the
> output will follow the input.  As the frequency of the input is increased
> the out put never gets to the maximum displacement and lags the
> input.  You
> can see this if you move your stick from side to side slowly and then as
> fast as you can go.  So bottom line, fast is good.
>
> Why expo you ask?  Expo is a means of getting better resolution of the
> "Man-Machine" system.  Assuming a degree of stick gives a degree of servo
> travel, one would have a hard time holding 0.1 degree.  With expo changing
> the relationship to a larger stick movement to get a given servo
> movement it
> is easier for the pilot to hold small angles of deflection.  That
> is he can
> resolve more precise servo/control surface position.
>
> Jim O
>
> ----- Original Message -----
> From: "John Pavlick" <jpavlick at idseng.com>
> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
> Sent: Thursday, September 14, 2006 9:49 PM
> Subject: Re: [NSRCA-discussion] RX choices
>
>
> > Jim,
> >  The heli guys can feel the difference between the "old" Futaba 1024 PCM
> and
> > the new G3 - or so I'm told. One of my friends just got a 14Mz
> and said he
> > had some interesting moments with his Rap 90 until he got used
> to it (the
> > 2048 PCM with fast frame-rate). I'm still amazed at how we use fast
> digital
> > servos, then add expo to soften them up. I know there's more to it than
> that
> > but it seems kind of silly in a way.
> >
> > John Pavlick
> > http://www.idseng.com
> >
> >
> > > -----Original Message-----
> > > From: nsrca-discussion-bounces at lists.nsrca.org
> > > [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of J.Oddino
> > > Sent: Friday, September 15, 2006 12:32 AM
> > > To: NSRCA Mailing List
> > > Subject: Re: [NSRCA-discussion] RX choices
> > >
> > >
> > > PCM works better than PPM when both are working.  When you receive a
> good
> > > frame of PCM it is perfect, that is, it is exactly what was
> > > encoded.  PPM is
> > > always corrupted by the RF link.  RF noise shows up as pulse jitter in
> the
> > > decoded signal.  This is usually only noticed when the signal to noise
> is
> > > low as it might be at long range with bad antenna
> orientation.  This was
> > > very apparent in the PPM-AM systems that proceeded PPM-FM.
> > >
> > > The PCM system only has to decide it there is a pulse present or not.
> The
> > > PPM system must accurately measure the time between pulses.  This is
> easy
> > > with nice square pulses but impossible with distorted rounded pulses.
> The
> > > net result is the PCM will work better and this is easy to demonstrate
> at
> > > max range.
> > >
> > > The Berg and Multiplex receivers that use Digital Signal
> > > Processors minimize
> > > the jitter by essentially filtering the PPM signal.  I'm not
> sure of the
> > > algorithms used but typically filtering adds a delay.  Apparently
> > > it is too
> > > small to be detected by RC pattern pilots.  It would be
> > > interesting to know
> > > if the heli guys can detect it.
> > >
> > > Jim O
> >
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