Receiver Choices/PCM fail safe

[Troy Newman]

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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> >
> > =====
> > 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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