[NSRCA-discussion] RX choices long club testing results

[Keith Black]

Wayne,

This is a great report and IMO should be turned into a K-Factor article.
Are you listening Mike? ;-)

I fully agree with the practice of having a Safety Office at local clubs and
contests asking pilots to turn off their radios to make sure the f/s is set
to low idle. It seems that not a year goes by where I hear about some awful
accident where a plane takes off due to f/s not being programmed and people
are endangered, hurt or in some cases killed. I just don't get why people,
especially with large planes, won't go to PCM (or FM with signal processing
and f/s). Now with the cheaper RX's there is no financial excuse, I guess
it's simply an education issue.

Wayne, thanks for your report.

Keith Black

----- Original Message ----- 
From: "Wayne" <Whinkle1024 at msn.com>
To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
Sent: Thursday, September 14, 2006 3:30 PM
Subject: Re: [NSRCA-discussion] RX choices long club testing results


> Bob, I understand how it works. The Carrier signal is still FM and I
> understand that. The fact that the signal is digitally encoded and how it
is
> encoded rejects bad signal or noise or what ever you call it better than
> straight PPM. I spoke to a semi local Team JR guy at a contest and he told
> it was like a little email package with PCM to simplify it. If the email
was
> formatted properly then the RX said OK you are my daddy. If the signal was
> not formatted properly it would reject it in favor of the proper format
and
> if none was found it would do what the Failsafe setting told it to do. In
> some cases that is Hold the last input on the channel and if you program
it
> to go to a specific position it would. In the case of straight PPM if the
RX
> sees the signal it passes it through after its been filter and so on. This
> is why you see a glitch in FM(PPM) and not in PCM
>
> Am I right?
>
>
> I know that F/S doesn't right the model but in reality if you are getting
> radio interference would you rather have the model do something
predictable
> like low throttle and hold other controls or do something totally
> unpredictable. I have played with F/S in the air by turning my TX on and
> off. The return of the signal is very very fast like a second or so. My
> thinking is that if you have enough interference to make the model go into
> hold "Lockout" for long enough to crash then I think its reasonable to
> assume this interference is bad enough that the model may very well not be
> controllable?
>
> We did some testing last fall at my local club as guys had questions about
> this subject. This followed a serious accident in which a 40% model at a
> Giant Scale fly-in was controlled by a little $60 FM RX and went to full
> power and cut through the pits and into another modeler. This guy almost
> died. A tragic event for sure but a $3000 or $4000 model controlled by a
$60
> RX? one of our club members was a witness to the event and came home with
a
> major agenda for our club to implement. Our club was  looking at a PCM or
> aftermarket F/S device requirement to help mitigate issues. Our big
concern
> is as with all flying sites the homes are getting closer and we don't want
a
> model heading off to meet the local neighborhood.
>
> We flew some trainers and foamy models. We took models high and simulated
> PCM F/S and shoot down situations. For our tests we only used Futaba and
JR
> radios. These were higher end TX's as we used the synth capabilities on
some
> of the systems to create the issues (JR 9303, 8103, 10X and Futaba 9C'S
and
> 9Z's also a 14MZ). We tried lots of different frequencies throughout the
> band. We used everything from little hitec foamy size rx's to the top of
the
> line 14MZ 2048 stuff. In the cases of the PCM system we found that in most
> cases the Futaba and JR PCM stuff was pretty bullet proof even in a shoot
> down. It took a very close TX of the same brand to cause a PCM HOLD
> condition (our test had engine go to Idle so we could hear it go in and
out)
> If the radio brands were mixed JR flying and Futaba as the shoot down it
was
> a rare blip of throttle and the longest hold was on the order of maybe a
> couple seconds. In the case of same brand shoot down the model would go
into
> PCM hold for longer until the shoot down TX was off. Then immediately the
> model was in full control again. Sometimes we could not even tell the
shoot
> down TX was on until its antenna was extended or the primary antenna was
> collapsed partially. If the primary was PCM and the shoot down TX was in
FM
> mode it was almost a non existent problem. A very very rare blip of power
> when the shoot down TX was closer to the model than the primary. And this
> was only with the shoot down antenna extended more than about 1/3 to 1/2
> way. In other rare cases the shoot down TX actually became the primary and
> started controlling the model. This was rare but we did se it happen. The
> 2048 didn't do it but the 1024 JR and Futaba stuff could easily. In fact
we
> had two 9303's and copied the program between them. We just swapped off
the
> TX that was off, then the pilot that was flying would shut his TX off and
> the next guy turned his on. Man it really was a cool experiment and proved
> the reliability and consistency of the systems.Pilot saying ready off, #2
Ok
> I'm on, got it.
>
> Our club was very impressed with the PCM rejection of the signal. In fact
I
> felt the model was in many cases better in control with the PCM holds
going
> in and out than the FM responses. The model never flipped upside-down,
never
> snapped or went wild. It just held its path and input. If that happened to
> be a roll or loop it would continue to roll or loop at the given rate but
> that was all. The other note was many club members felt PCM hold was a
> forever lockout thing meaning the hold meant the model was going to crash
> period and they wanted to have some control. Well we never had that. Once
> the interference (shoot down TX) was off every single time the primary got
> immediate control. And I mean right now as if it never had the issue
coming
> back.
>
> The FM systems in the same test didn't care about brand of TX, and didn't
> care about distance or antenna extension on the shoot down TX. In fact
most
> cases the models became uncontrolled and while it would still respond to
the
> primary TX in the middle of some of the glitching the models were just
> basically all over the place. It seemed like the RX was passing just any
> signal through. Of big note if the shoot down TX was FM mode also the
models
> were glitchy but the primary could still have an effect not really to fly
> the model in a save situation but it had an effect. . If the Shoot down TX
> was PCM there was no hope. The models were literally all over the place
and
> yes some primary control was getting through but you could not rely on the
> input to fly the model.
>
> We conducted this testing on several weekends and with lots of club
members
> present. Yes we took some risks but we really wanted to see if there was a
> difference. The result of this test made my local club hit the hobbyshop
> with a huge order of PCM RX's. I think he sold like (25) JR R770's over
the
> course of the next week. The old guys in the club found out their model
was
> better protected using the PCM over their FM and it was a black and white
> comparison. Besides most sport models they guys are flying are in the
> $400-800 range and what is the extra $40 from the R700fm to the R770pcm.
Now
> both of these are Synth so that is cool too.
>
> Our club now has requirements for a F/S device or PCM on all models over
> 7lbs. Why 7lbs? well we felt that we didn't want to discourage trainers
and
> new folks starting out, but we did want basically anything 60 sized and
> bigger to have some F/S capability and the club rule is a safety officer
can
> ask you to show it before you fly. I know most of the GS fly-ins in our
area
> and the Joe Nall now require this. Before you take off the flightline
> official asks you to turn off your TX to prove a low throttle setting. The
> groans came from the old guys for sure, but in the end they were the ones
> that really felt the clubs responsibility to our neighbors and to our
selves
> was more important. The next thing was a phase in period of 1 yr. We are
now
> coming up on that 1yr and the rate of crashes has dramatically reduced at
> our field. The concern was older FM TX's that could not use do PCM well H9
> answered the call with a  $20 F/S module for use on FM systems. Now I
think
> there are 3-4 different brands out there. So for the cost of a gallon of
> fuel and a few props you can have PCM or a FS device for FM.  We have a
log
> book that you are suppose to log any crashes or mishaps. We use it to razz
> the guys and also to keep track if we have an issue on certain channels or
> with a  specific brand or RX or the like. Well the 2005 log book was
always
> an issue of radio quit, glitched or what ever. Since the testing and mass
> exodus to PCM the crashes are greatly reduced and top it off the crashes
we
> are having with radio issues are the type of stuff than you would see like
> dead battery or bad switch not the mystery glitch or I got hit. Guys now
> know what radio problems look like and they are diagnosing crashes better
> and preventing them. Now with everybody flying PCM its really rare to see
> radio problems at the field. Our field is mostly JR thanks to our
semi-local
> Team guy. The most common radio now is the 6102, 8103 and the 9303.
>
> Seems that pattern guys tend to spare no expense in the TX department lots
> of 9Z's and 10X's as well as the 9303 and 9C systems yet I'm seeing many
use
> a PPM RX. My curiosity was peaked as I would have expected nobody to use
FM
> in this group. Before the NATs the young man was having issues with his
> system and when he told us what he was using for servos, leads and radio
> gear I was shocked. A competition level pilot using aftermarket extension
> leads and FM Rx'. I was always taught to stay within the brand. Servos are
> OK to mix brands with but for switches, extensions, and RX's stay in your
> own yard the OEM stuff is just a dollar more you have less trouble with
it.
> The models are expensive and we spend hours and hours building and
trimming
> them up. The real cost in loss of a model is the time trimming and setting
> up a new plane to be just perfect. The Money is one side but to me its all
> the time and passion working toward the perfect flying model. It sucks
when
> you are 1/2 way there or even 99.99999% and the model is gone hit the CLR
> key in the TX and start over with a new one.
>
> Just passing on some experience we had with it. We proved to ourselves
that
> PCM not only protected our people and neighbors better but it saved more
> airplanes too. I understand we really only tested a single condition shoot
> down situation and real interference is more random and rare in the real
> world. We felt that the shoot down was the worst case situation for our
> field as we are our away from industrial areas and other noisy environment
> stuff. We do have some homes about 1/2 mile back behind our pit area to
the
> south but models are never flown back there. We have a rule to keep
> everything North of our runway.
>
> By the way lots of guys locally are using the Spectrum DSM as it has a
> failsafe like PCM and it works great in those small parkflyer models. One
> guy is even flying it in his 40 sized trainer converted to electric.
>
> thoughts?
>
> Wayne
>
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