Conference vmszoo::rc

    Kay,
    
    Guess I never picked up on that one; frankly I'm not sure just "what"
    it might be or why you'd want it but, if I had to guess, it sounds
    like [maybe?] the rudder can be set up such that rudder throw varies
    as a function of throttle position, i.e. max throw at low throttle,
    min throw at high.  Might have some application in pattern, maybe
    even squirrelier taildraggers but I don't think I'd want it if I've
    hit anywhere close to what it "really" is. 
    
    Adios,	Al

    Another guess is that it switches "automaticly" togehter with ailerons.
                                          
    Regards
    

	My JR radio has this feature and yes it can be usefull in pattern
	but like all things, has a tradeoff or two.

	What it does is allow for the rudder dual rate to automatically
	switch on or off depending on the setable position of the throttle
	stick.  Typically, you set it so that you have low rate at high
	throttle and high rate at low throttle.  This gives a lot of rudder
	authority for low throttle manuvers like stall turns and start of
	the takeoff roll but smooths things out for slow rolls, point rolls
	and general correction during full throttle flight.

	Only thing I've found I don't like about it is that if you give a blast
	of throttle in your stall turn, the rudder suddenly goes from full
	high rate deflection to full low rate deflection which defeats the whole
	purpose of the blast of throttle to swing the tail over.

	Just another "goodie"?? to keep track of with all the other rate/mixing
	//// switches.

	Ron

    Ron,
    
    Sounds like my guess was right on the money.  Like you suggest,
    another bell/whistle I'll be happy to leave to others, preferring
    to "fly" [sorry, Willie] my own aircraft.
    
    Adios,	Al

    Chris and Al,
    I wish you guys would leave off the "quotation marks" [sorry, willie].
    
    Ken
    

    I understand the basic theory of AM and FM audio broadcasting but I
    am curious as to how this applies to R/C transmitters.  Is the
    tranceiver always transmitting or does it only send when when the
    controls are moved?  How are the channeds multiplexed onto the
    operating frequency; does each channel use a different frequency
    or is it a coded transmission? Etc.
    
    	Jeff Gilbert CSC/AT

    Jeff,
    
    I can speak to yer' question only in the most basic terms but, perhaps,
    that's the form you'd most easily grasp as you, like myself, are
    apparently not an electronics type.
    
    The Tx (transmitter) is sending a signal at all times once turned
    on, sending a series of reference pulses, one per function (usually
    incorrectly called channel), to the Rx (receiver) on a single frequency.
    Each pulse is a specific width at neutral and operating the applicable
    function's control (let's say elevator) varies this pulse's width
    plus or minus it's neutral value by an amount directly proportional
    to the amount the control was moved.  This series of pulses is repeated
    many times per second so the slightest change from neutral is noted
    and sent along to the Rx.
    
    In the airborne package, the Rx receives and decodes the pulse train,
    detecting any change(s) from neutral and compensating by moving
    the affected servo(s) an appropriate.  
    
    The newer types of encoding, like PCM (Pulse Coded Modulation) and
    PPW (not sure what this means) are somewhat different but a basic
    understanding of the above is sufficient knowledge for most of us.
    Being an expert at operating theory has no bearing on how competent
    a pilot one becomes or how much enjoyment he derives from the sport.
    This is quite fortunate as most of us have very little knowledge
    of what makes our radios work...recognizing when they're broke is
    the key. 

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

    I have a little more to add to Al's description of how RC works.
    AM and FM refer to the type of carrier modulation but the same
    information is transmitted by either type of transmitter.  The carrier
    is modulated by a series of pulses called a frame.  There is a chip
    in the transmitter that takes the voltage from the joystick pots
    for each 'channel' and generates a series of pulses.  The width
    of each pulse encodes the joystick position.  Each frame consists
    of  a pulse for each 'channel' or function that the radio encodes
    and the receiver decodes.  For AM, the carrier is just turned on
    and off, on when the pulse is high, off when the pulse is low. 
    The receiver demodulates this and reproduces the series of pulses.
    A chip in the receiver called a decoder separates these pulses and
    sends them to the appropriate servo.  The servo has a chip that
    decodes the desired position from the width of the pulse that it
    sees.  For FM, two frequencies are transmitted, one when the pulse
    is high, another when it is low.  The receiver decodes this and
    again reproduces the series of pulses.
    	PCM is another method of encoding the positon information that
    has more reliability due to some error detection capability.  THis
    is what is used in most garage door openers to encode your personal
    code so that your neighbor's control won't open your door even if
    it is on the exact same frequency.  In rc, everyone has the same
    code, but if the signal gets corrupted, the receiver knows and can
    prevent doing the wrong thing.  It can't uncorrupt the signal but
    it can prevent glitching.  Most PCM sets have a failsafe mode that
    can put all the servos in a preset position if signal is lost for
    more than a second.  This can at least prevent flyaways but it doesn't
    prevent crashes.  The biggest advantage to PCM in my opinion is
    that you can fly through interference without getting full control
    deflection.  The servos will hold last output until the signal is
    good again or fail safe takes over.  If most of the frames are getting
    through, you don't even know that you have some interference.  With
    conventional AM or FM, the surfaces would be glitching and chattering
    due to the servos reveiving some wrong pulses mixed in with the
    right ones.  By the way, PCM generally uses FM for modulation. 
    I microprocessor is required in the receiver to do the smart things
    like failsafe mode.  This boosts the cost and power consumption
    of the receiver.  PCM is the most reliable system we have as of
    now.  In the future, maybe we will have error correction capability
    as well as error detection.   Sorry for being long winded.
    
    Charlie
    
    

    Nice description Charlie.

    It's been over a year since I looked at the output of my Futaba
    Conquest with a scope, so I could be wrong, but...

    I think for AM Modulation, the transmitter is transmitting most of
    the time and off only when the pulses are transmitted.  (Carrier on
    for a low signal and carrier off for a high pulse.)

                                - Dan Miner

	What happens with my Futaba AM sets (i've had them on a scope)
	is that the transmitter is on most of the time and is turned off
	for very short periods to delimit the pulses. It looks something
	like...
                          <ch 1><---ch 2---><--ch 3--><--etc
	tx on  ----------+ +---+ +---------+ +-------+ +----- etc
                         | |   | |         | |       | |
        tx off           +-+   +-+         +-+       +-+

	After the signal is de-modulated at the receiver you've got
	a string of narrow pulses. The time period between
	pulses determines what position each servo goes to. The high time
	between pulses is somewhere around .5 to 1.5 msec (10**-3 sec)
	depending on where the transmitter sticks are held at
	and the low time is maybe .1 msec. After the last pulse in a frame
	the TX is left on for a longer period (longer than 2 msec or so) and the
	decoder in the reciever detects this longer than normal period to
	decide when it should start looking for the start of a new frame.

                     !
                   --+--
G. Schrader     o___<0>___o    CSS::SCHRADER
                  *  *  *

    You're both right about the tx being on during the non-pulse period.
    That's so the AGC in the receiver has the signal to average on.
    The frame is defined by the larger space between the first and last
    pulse.  The decoder looks for this large space and syncs on that.
    The major cause of a glitch is if something fills in that large
    space.  Then the next frame gets shifted to the wrong channels.
    If someone turns on on your frequency, he is sending an assyncronous
    frame of pulses.  The receiver will detect both of them and the
    decoder will not be able to send the correct pulse to each servo.
    This can cause a full throttle pulse to go to the elevator channel
    for example, giving a full up or down command to the elevator servo.
    
    Charlie
    
    

>    If someone turns on on your frequency, he is sending an assyncronous
>    frame of pulses.  The receiver will detect both of them and the
    
    Charlie,

    If someone turnz on on your freq, he is an ASS-ynchronous source of
    interference.  Well put, subtle, yet succinct, I like it.
    
    

>>    does any one make a radio that has a proportional 5th channel or
>>    even 6th?

    Sure, just about every popular manufacturer does!  The first four
    channels are on the two sticks (typically), and extra channels
    are on slide pots (still proportional but usually no trim on them),
    or an on/off switch for bomb drop or landing gear.

    On the Futaba 7FGK you have the 4 standard channels, two more channels
    on slide pots on the front of the transmitter (below the sticks)
    and one on/off channel.
    
    The Airtronics CS7P is the same except that the slide pots for channels
    5 and 6 are mounted on top of the transmitter.
    
	
    Bill

    Dan,
    thats a good idea about building some covers for the switches. How
    you going to do it? You might also consider passing that problem
    back to the manufacturer. Maybe they'll send you some free decals
    to make up the loss of your plane. 8^)
    
    Dan Eaton

    Gee I knew I liked JR for some reason,They all have guards on the
    sides of the on off switches. Also the switches are low profile.
    
    
    Dan, a suggestion might be a small wire loop that is just long
    enough to be placed over the switch when it's in the "on" position.
    
    Tom

    
    I knew a guy in CXO who used to leave his RX off on his sailplanes.
    Kind of a bitch when you hurl the ship and hit the winch. He made
    a set up where by a metal pin was inserted into the side of the
    fuse. To this pin he attached a ribbon. When the pin was removed
    the RX went "ON" He then inserted the pin into the TX . This turned
    the TX "ON".
    
    
    It worked
    
    Tom

    yeah, i wish every rc transmitter had a lock-out feature on the
    on/off switch such that you had to insert some kind of (standardized)
    key to turn it off.  this key could then be put on the freq pin
    so you can't turn on till you got the pin and you can't return the
    pin without turning off.  of course each radio would be sold with
    a key so you could defeat the whole system, but most shoot-downs
    are accidents which i bet the above would prevent.

    Dan, if it's any consolation I'm sure you're not the first idio... I mean
    poor guy that's done that to himself.

    My Airtronics transmitters have a plastic thing that is screwed on over
    the slide switch that has side plates that stick up as high as the
    switch on each side. You have to kind of stick your finger down between
    the plates to slide the switch - much more difficult and different than
    the trim sliders. I would think you could construct something like that
    easily enough, or maybe even buy one.

    I've also seen (don't remember where) a spring loaded cover that you
    have to flip up to get at the switch. I think it was for a standard
    wall switch so you might find one at an electrical supply house. It
    wasn't too big to consider using on the transmitter.

    A final comment - if the trim is off by enough that I have to hold
    the stick and can't momentarily let go of it to adjust the trim with
    the same hand, I try real hard to yell and get somebody to do it for
    me. I don't recommend reaching across with the other hand to adjust
    the trim, you might hit the power switch by mistake...

    Dave

    
    re: .-1  what is the price of it?
    
    Bill

    
    I agree that the drop you were seeing is normal.  The extra potential
    up and above 4.8v bleeds off pretty quick with a load, and slowly even
    without a load.  If you used Charlie's cycler then he probably gave you
    one of those nifty printouts that show the discharge curve of your
    battery pack.  Pretty neat, huh?
    
    Bill

    
    Charlie has already graciously offered schematics and software, but
    I've been too lazy to do anything with it.  I'd want to convert it
    to my son's Franklin (Apple) computer and probably put a serial
    interface on it.
    
    Bill

    I actually started to build a Watt-O-Meter for my PC.  Charlie gave me
    the schematics almost a year ago.  I started to redraw the schematics on
    a Schematic-CAD program for the PC, but, like Bill, ran out of
    time/motivation to complete my efforts.  I do intend to start doing it
    agin soon, though...

    Dan,
    	THis design would work in the tandy 1000 since it is IBM
    compatable.  I'm too busy to work with you during the next couple of
    months but I'd be glad to help you get one going on your computer. 
    Then you could help cycle batteries for people near your area.
    
    Charlie
    

================================================================================
Note 104.1                     Generic Radio Note                        1 of 10
AKOV11::CAVANAGH "R/C planes..The bigger the better" 32 lines  19-FEB-1990 09:43
                     -< The transmitter could be crap... >-
--------------------------------------------------------------------------------

  This weekend I took out my Futaba Conquest that was in the late J3 and did
some range testing.  Here is what I found....

  
   While standing right next to the receiver everything was solid until I
started shaking the transmitter  Every so often the servos would twitch.
I placed the receiver on the floor (all testing was done inside my living room)
and started to walk away.  As I was walking I accidentally bumped the antenna
on my leg (it was still collapsed).  The servos jumped when this happened.  I
was able to recreate this response by simply tapping on the end of the ant.
When I pointed the ant. away from the receiver (at a distance of about 10 feet) 
the servos jittered like crazy.  I was still able to give input via the sticks,
but the jittering continued.  At a distance of about 15 feet I put the ant. up.
The jittering continued no matter which way I pointed the ant.  So I turned the
transmitter off and the servos were quiet.  Turn it on and again they jitter.
I unscrewed the ant. and the servos went wild.
  I tried to make the receiver fail by shaking it and tugging on the wires and 
ant. and anything else at that end, but I couldn't get it to glitch that way.

  So my conclusion (correct me if I'm wrong) is that my transmitter is 
malfunctioning.  It could be a bad crystal (as suggested by others) or a bad
wire or........???

  What I would like to do is get together with someone who has a ch 46 
transmitter and see if my receiver acts the same with their transmitter as 
it does with mine.  That would help narrow it down.  The next DECRCM meeting 
would be a good time/place to do this.  

   Any volunteers?

			Jim

Hi Jim,
I just came across your note during my weekly scan of the DECRCM
notes file (man I hate this 2-conference fiasco!).  Anyhow,  here
are a few comments...

>>>I placed the receiver on the floor (all testing was done inside my living
>>>room) and started to walk away.

    The first problem may be the fact that you did this test inside your
    house.  This is not a good environment for radio testing because of
    all the reflected signals your receiver will be getting.  I suspect
    this is the main cause of jittering, and suggest you try it in the
    open outdoors (where it really needs to work!).

>>>As I was walking I accidentally bumped the antenna
>>>on my leg (it was still collapsed).  The servos jumped when this happened.  I
>>>was able to recreate this response by simply tapping on the end of the ant.

    Touching the antenna with anything even slightly conductive can affect
    the signal quality.  If you suspect a loose connection, push the antenna
    around using the eraser end of a pencil or something similar (also do this
    outside).  If there is no change in the servo jittering, you probably
    don't have a loose connection problem.

>>>When I pointed the ant. away from the receiver (at a distance of about
>>>10 feet) the servos jittered like crazy.  I was still able to give input
>>>via the sticks, but the jittering continued.  At a distance of about 15
>>feet I put the ant. up.  The jittering continued no matter which way I
>>>pointed the ant.  So I turned the transmitter off and the servos were
>>>quiet.  Turn it on and again they jitter.  I unscrewed the ant. and the
>>>servos went wild.

    Again this sounds like it could be because you were inside the house
    and getting reflections from windows, walls, etc - especially given
    the fact that it seemed to get worse when you extended the antenna!

>>>I tried to make the receiver fail by shaking it and tugging on the wires and 
>>>ant. and anything else at that end, but I couldn't get it to glitch that way.

    I'd recommend caution when you do this because you could end up breaking
    or damaging the very wires you are trying to check!

>>>So my conclusion (correct me if I'm wrong) is that my transmitter is 
>>>malfunctioning.  It could be a bad crystal (as suggested by others) or a bad
>>>wire or........???

    I doubt if it would be a crystal problem.  See how it acts outdoors.
    Let's face it, AM systems are not going to be as bulletproof as the
    new FM/PCM systems, but I wouldn't jump the gun and give up on it yet.

    If none of these things help, we can look at the output of the transmitter
    on a spectrum analyzer here in our lab.  This would quickly narrow down
    whether it was a transmitter or receiver problem.

    We can discuss this publicly in the RC conference if you would like,
    but I'm read-only (and not very often) with DECRCM until something
    is resolved to get everyone into one conference again.

Bill

    Here is another radio question.  What is the compatibility between tx
    and rx with different numbers of channels?  For example, I have a
    Futaba 4NBL (AM).  Will it work with a 2 channel AM receiver? 

    Well nobody seems to want to answer my question.  I asked Futaba and
    they said no, it would not work, although I cannot understand why. 
    Also, they seem to sell sets where the tx is say 5 channel and the rx
    is 7 channel, so it obviously works for the tx to have less channels
    than the rx, so why not the other way round?

>            <<< Note 473.37 by COOKIE::R_TAYLOR "Richard Taylor" >>>
>                          -< #Channel compatibility? >-
>
>    Here is another radio question.  What is the compatibility between tx
>    and rx with different numbers of channels?  For example, I have a
>    Futaba 4NBL (AM).  Will it work with a 2 channel AM receiver? 

I didn't answer because I wasn't sure of the answer.  That is I have
never had the Futaba 2 channel AM receiver and a Futaba 4 channel
AM transmitter.  But I can answer the back end part of the question.
Why.

Because a 4 channel set is set up so that
  (generally now - be careful not to quote me)

  Channel 1 = Ailerons
  Channel 2 = xxx
  etc.

Now if you power up a two channel Rx on the same frequency
and you are flying with only Rudder and Elevator then they had
to swap around the channel assignments.

Sure enough I had an Airtronics 4 channel FM Rx and 6 channel FM Rx
and when I switched Transmitters the sticks would control different
channels.  I had to move the servo connectors into different channels
to get it to work.

In other words you need a Map and a guide to determine if a specific
Tx is compatible with another Rx in terms of channel assignments.

The only thing you can be sure of is if you have more than 4 channels
the first 4 channels will map to the two control sticks.  In some
order Aileron, Elevator, Throttle and Rudder sticks will be the first
4 pulses send down the RF stream and any "Compatible" 4 or more channel 
receiver will route those 1st four channels to some existing servo connector.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

>>  compatibility between tx and rx with different numbers of channels?  

    I suspect (but without having owned/used a zillion different systems, I
    cannot be absolutely certain) that the general rule is that they will
    be compatible.  My own experience is this:

    	Receivers:	6 channel Airtronics dc FM    #92765
    			4 channel    "        " "     #92745

    	Transmitters:	6 channel Airtronics FM  Vanguard VG6DR
    			4 channel    "       FM  Vanguard VG4R
    			7 channel JR X-347 PCM used in FM mode

    All of these receivers work with all of these transmitters.  Re Kay's
    comment about re-ordering of the servo plugs --- there is no
    re-ordering when Airtronics receivers are used with Airtronics
    transmitters --- not with these, anyway.  JR ordering *is* different,
    but that is a JR issue, not a channel number issue.

    Re-ordering is a nuisance, not a problem *EXCEPT* if you use more than
    one transmitter with a particular receiver --- then you can get bitten
    much the same way that different servo reversing settings can bite you.  
    Careful pre-flight checkouts become very important.

    There are some very real incompatibilities:

    	between frequency bands and between frequency "channels"
    
    	between "modulation" technologies  (AM, FM, PCM)
    
    	between manufacturers (for FM and PCM)

    	between product lines of a manufacturer (for some PCM systems)

    I think that all of these are discussed in this file; do a 
    
    	Notes> SHOW KEY/FULL RADIO*COMPAT
    
    and read the appropriate 11.whatever note listed thereby.
    
    I suspect that most 2 channel receivers are car/boat receivers on 75 mHz.
    That would make them incompatible with a transmitter on 72 mHz and
    might be the basis for the response by Futaba.
    
    Alton

>    All of these receivers work with all of these transmitters.  Re Kay's
>    comment about re-ordering of the servo plugs --- there is no
>    re-ordering when Airtronics receivers are used with Airtronics
>    transmitters --- not with these, anyway.  JR ordering *is* different,
>    but that is a JR issue, not a channel number issue.

Whatever Rx comes with the Vanguard 4 ch system (It is a 6 or 7 ch Rx)
is not servo plug ordering compatible with the Vision SP Tx.

i.e.  When I bought my Vision SP I had to move the plugs in the Sagitta
and could not use the old Vanguard Tx as a backup.  This required surgery
to get to my Rx and move the plugs.

Smart computer radios should be able to map any function to any channel
number.  I don't know that anybody is doing this however.  The
Airtronics Vision and Futaba 9VAP do not.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################