Receiver Choices/PCM fail safe

Mon Sep 30 20:49:09 AKDT 2002

Jerry,

I've heard people say they use failsafe settings to put the plane into a
downward spiral or gentle circles etc., but in my opinion that is really a
bad idea. The problem with any preset settings, other than throttle back, is
that as Troy mentions most hits are very short interruptions in the signal.
So what ends up happening is you're flying along just fine and all of the
sudden your flight surfaces deflect to the failsafe position and then
quickly back again. When this happens there's no telling what position your
in, but in most cases it's going to cause more of a problem than if the
control surfaces all just held in the same position they were in. It would
be pretty sad for someone to loose their plane because their fail-safe
settings sent the plane into a spin and out of control just because it took
a two second hit.

Personally when flying PCM I have all control surfaces hold except for the
throttle which I drop to a low idle, but not low enough to kill the engine.
I've heard that some pattern flyers even hold the throttle so any hits will
have the least possible effect on their pattern when flying in a contest,
but I personally wouldn't do this.

What got a lot of this talk going is the situation where a plane went into
failsafe mode and flew quite a distance and hit and killed a young child
(this is what I heard, don't know if it's true). I don't think this is much
of a danger if you freeze all control surfaces except for throttle which you
put into a low idle.

Keith Black

----- Original Message -----
From: "Troy Newman" <tanewman at qwest.net>
To: <discussion at nsrca.org>
Sent: Monday, September 30, 2002 10:21 PM
Subject: Re: Receiver Choices/PCM fail safe

> Jerry,
>
> It is very rare in fact its so rare I have only seen it happen a few times
> in almost 22 years of flying...that a plane going into failsafe on a PCM
RX
> will lock out indefinitely and stay in hold until it hits the ground. The
> only times I have seen it is when there is a serious problem with the
> TX....like battery pack dead or something like this....
>
>
> Usually what happens is the RX will get interference (meaning bad signal)
> and will hold or go to failsafe position for a very short amount of time.
> This could be a sec or less sometimes its more...but in most cases the
model
> stays on track and the pilot pulls up and nothing happens then the plane
> leaps up as the communication is regained.
>
> Fail Safe is not intended to save an airplane....nor is it intended to
crash
> an airplane. Rather it will give the servos a predicted position to go to
> and hold...whether that was the last input of it was the pre set
> position.....either way the result you get from a Fail Safe condition is
> predictable. With FM or PPM Rx's you may get anything that is floating in
> the air......this can cause the plane to act violently and sometimes break
> the plane, the servos gear trains, the control surfaces,
> ect.......Interference is interference and its bad no matter what. I
choose
> PCM because it is better at the rejection of interference and it gives me
a
> predictable position for the servos......
>
> Some guys say when if it wasn't in fail safe I could have saved it.....yea
> right! It was in fail safe because your super human skill could not
generate
> the proper formatted signal to the tell the RX what to do......if it
crashed
> in fail safe its because you were getting interference anyway and had no
> chance or at least little chance of saving it.
>
>
> If you have interference issues get your equipment checked out......don't
> run FM because then you can see it. The thing some people bring up about
PCM
> is that it masks the interference so you don't know it. I honestly believe
> that if the interference is not felt by you the pilot and you never know
it
> was there.....then the PCM technology did its job!
>
>
> Now you should range test your equipment to the extreme and find out where
> things die....and keep checking this over the life of the equipment....its
> like a good car it will tell you the brakes need work....it will tell you
> the power steering pump is going out.....you just need to listen....
>
> Check out the article written in the Horizon Quarterly about a year
ago...it
> is available on the Horizon web site...
>
> www.horizonhobby.com
>
> Look under past articles.....It has a very good procedure to range test
your
> plane.....it also discusses the advantages of PCM and what you can do to
> find out when your radio needs a new set of brakes.......
>
>
> I have found that over time a couple seasons the output transistor in all
> the brands.....JR, FUT, and AIR will become weaker.....Have it replaced
when
> you see the degradation in range.....
>
>
> But to answer your question my opinion is PCM is the ONLY way to fly...its
> safest for you, your plane and the people and property around you.
>
> I know some will disagree but I have been running it since 1987 on both
> Futaba and JR radios......It is worth it.....It has saved planes countless
> times when I have had a problem with radio gear......it acts as an early
> warning system.......I'll pull up and nothing then all of sudden the plane
> responds...Land it! and get the radio gear checked out.......at the time
it
> was a synthesized module on a 9Z.....but failures and problems can happen
> with any radio gear.....regardless of age....components can fail...and
> sometime do with a little help from us.
>
>
> By the way I always recommend hold on all flying surfaces......low
throttle
> is good but I don't usually do it......I know of a guy that puts his gear
> down.....it doesn't matter if its going to crash a F/S position will not
> stop it.....and a hold setting may keep the plane flying on its track
until
> signal is regained......Like I said I have only seen a few cases of total
> F/S lock out and the plane flying for any length of time.....its really
> rare...usually the RX gets a good signal back in at worst case a few
> seconds.
>
> Troy Newman
>
>
> ----- Original Message -----
> From: "Jerry Wilson" <jerrywil at swbell.net>
> To: <discussion at nsrca.org>
> Sent: Monday, September 30, 2002 7:36 PM
> Subject: RE: Receiver Choices/PCM fail safe
>
>
> > I've heard it suggested that the right way to program a fail-safe/hold
> > position was to be sure a plane which was no longer under control was
> > brought to earth quickly so that the danger was minimized.  In other
words
> > the fail safe is to protect other people and property, not the
operator's
> > model aircraft.
> >
> > Personally I have not done this and am reluctant to do so.  But they
have
> a
> > point.
> >
> > Would like to hear comments from the list.
> >
> > TIA
> > Jerry Wilson
> > Houston, TX
> >
> >
> >
> > -----Original Message-----
> > From: discussion-request at nsrca.org
> > [mailto:discussion-request at nsrca.org]On Behalf Of Tony Stillman
> > Sent: Sunday, September 29, 2002 7:26 PM
> > To: discussion at nsrca.org
> > Subject: Re: Receiver Choices
> >
> >
> > The PCM receivers are what I like best, due to the fail-safe/hold
feature.
> > However, I use less expensive PPM receivers in my "sport" planes.  Most
> > times, you will NEVER see the difference between the two.  The PCM will
> work
> > in high noise (make that interference) areas much better than PPM
> receivers.
> >
> > You should have confidence with either!
> >
> > Tony Stillman
> > Radio South
> > 3702 N. Pace Blvd.
> > Pensacola, FL 32505
> > www.radiosouthrc.com
> >
> > 1-800-962-7802
> > ----- Original Message -----
> > From: "RC Steve Sterling" <rcsteve at tcrcm.org>
> > To: <discussion at nsrca.org>
> > Sent: Friday, September 27, 2002 5:54 PM
> > Subject: RE: Receiver Choices
> >
> >
> > > You are right-- I was thinking of the 148DF (not the P)which is PPM.
> > >
> > > Now I really don't know what would differenciate them. Maybe Tony
> Stillman
> > > will check in.
> > >
> > >
> > > -----Original Message-----
> > > From: discussion-request at nsrca.org
> > > [mailto:discussion-request at nsrca.org]On Behalf Of Brian Young
> > > Sent: Friday, September 27, 2002 2:01 PM
> > > To: discussion at nsrca.org
> > > Subject: RE: Receiver Choices
> > >
> > >
> > > Thanks Steve, the 148DP is a PCM receiver also (listed
> > > as such on Futaba site). Part of the reason I am
> > > curious about the difference in cost between the
> > > three, I can see the difference for an added channel.
> > > But the large price difference for the 138DP has me
> > > quite curious. I mean why pay $30 more if the 138 does
> > > the same thing.
> > >
> > > --- RC Steve Sterling <rcsteve at tcrcm.org> wrote:
> > > > The 138DP is an 8 channel PCM receiver. PCM
> > > > transmits a digital data stream
> > > > like a modem and the receiver has a microprocessor
> > > > to decode it all.
> > > >
> > > > The 148DP is an 8 channel PPM receiver. An old
> > > > standby. PPM varies the width
> > > > of FM modulation pulses to communicate servo
> > > > position.
> > > >
> > > > The 149DP is a 9 channel PCM receiver.
> > > >
> > > > PPM receivers see interference or low signal as some
> > > > different pulse widths,
> > > > so they tend to cause the servos to jitter and jump
> > > > and be pretty
> > > > unpredictable when there is a problem.
> > > >
> > > > When PCM receivers get interference or low signal,
> > > > they either just stay
> > > > put, or go to a pre-programmed setting, like low
> > > > throttle, wings level.
> > > >
> > > > PCM receivers generally have cost quite a bit more
> > > > than the PPM receivers,
> > > > so the 138DP price is encouraging. There is much
> > > > debate, particularly on
> > > > this list, on which is better/more reliable. PPM
> > > > proponents say that they
> > > > see problems coming when the plane starts jumping
> > > > around, and with the
> > > > warning, may have time to get down and solve it. PCM
> > > > proponents say they
> > > > don't see as many problems in the first place, and
> > > > would rather have their
> > > > servos do predictable things when faced with
> > > > interference.
> > > >
> > > > I run PCM in my pattern planes, PPM (cheaper) in my
> > > > sport, funfly, float
> > > > planes, etc. No problem with either. Have seen
> > > > others with failures in both
> > > > types of receivers. Because equipment does fail, you
> > > > will get anecdotal
> > > > stories from both sides, but nobody has done a
> > > > scientific study to really
> > > > determine which is better, and under what condtions.
> > > >
> > > > -----Original Message-----
> > > > From: discussion-request at nsrca.org
> > > > [mailto:discussion-request at nsrca.org]On Behalf Of
> > > > Brian Young
> > > > Sent: Friday, September 27, 2002 11:24 AM
> > > > To: discussion at nsrca.org
> > > > Subject: Receiver Choices
> > > >
> > > >
> > > > Im looking to buy a couple new receivers, flying
> > > > Futaba so thats my area of preference. I have an
> > > > 8UAP
> > > > currently. I notice Futaba has available a new 8 CH
> > > > RX, 138DP for about $100, then they have 148DP for
> > > > about $130, and 149DP for $160.
> > > >
> > > > Each of these receivers have the required capacity
> > > > for
> > > > my plane. Can anyone enlighten me as to a method to
> > > > evaluate the price of the expensive one vs. the
> > > > cheap
> > > > one? Does the extra money bring more reliability,
> > > > etc?
> > > >
> > > > The 138 is a new model, so may have the use of
> > > > latest
> > > > technology, the other two have been around awhile so
> > > > maybe they are more of a proven design.
> > > >
> > > > And if anyone has any spares they want to sell I may
> > > > be interested.
> > > >
> > > > =====
> > > > Brian Young
> > > > Tulsa
> > > > b4598070 at yahoo.com
> > > > 918-745-6046h
> > > > 918-838-0900w
> > > >
> > > > __________________________________________________
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> > > > http://sbc.yahoo.com
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> > > =====
> > > Brian Young
> > > Tulsa
> > > b4598070 at yahoo.com
> > > 918-745-6046h
> > > 918-838-0900w
> > >
> > > __________________________________________________
> > > Do you Yahoo!?
> > > New DSL Internet Access from SBC & Yahoo!
> > > http://sbc.yahoo.com
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