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PICList Thread
'How to control an RC car'
1998\09\02@160229 by Norm Cramer

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I would like to know the easiest way to control an RC car from a computer
(could be a PIC).  I don't want the PIC on the car but to send the commands
to the car.  Ideally the car remains unmodified.

Thanks for any help.

Norm

1998\09\02@190058 by David Sprenkle

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I think a good way to control a RC car is to use the buddy cable that most
Airplane R/C units have.   Instead of connecting one end of the buddy cable to
another transmitter you could connect it to a PIC that could be talking to a
computer.  I don't really know what kind of signal the buddy cable is looking
for though.  You could use a Airplane transmitter with a crystal that is used
for cars.  The only drawback I could think of in this system is that you would
not get any feedback.

Norm Cramer wrote:

> I would like to know the easiest way to control an RC car from a computer
> (could be a PIC).  I don't want the PIC on the car but to send the commands
> to the car.  Ideally the car remains unmodified.
>
> Thanks for any help.
>
> Norm



--
David Sprenkle

1998\09\02@222220 by Sean Breheny

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Hi Norm and David,

I'm not a real expert here, but I think that you may have a problem with
using the buddy cable idea. Don't RC cars use a different set of
frequencies than the RC planes?

Well, if there is any way of getting it to work, I think that the
transmitter expects to find a variable resistance at several of the pins of
the buddy cable. I don't think that the trainer transmitter actually
generates any signals, I think that the buddy cable simply reads the
control pots.

I'd bet that a PIC wouldn't have aproblem generating the PWM that is the
actual modulating signal. If so, you could just canibalize a transmitter
for its RF unit and feed it the signal from the PIC.

I'm sure someone else on the list can shed more light on this. Perhaps Andy
Kunz?

Good Luck,

Sean


At 05:58 PM 9/2/98 -0500, you wrote:
>I think a good way to control a RC car is to use the buddy cable that most
>Airplane R/C units have.   Instead of connecting one end of the buddy
cable to
>another transmitter you could connect it to a PIC that could be talking to a
>computer.  I don't really know what kind of signal the buddy cable is looking
>for though.  You could use a Airplane transmitter with a crystal that is used
>for cars.  The only drawback I could think of in this system is that you
would
{Quote hidden}

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1998\09\03@011616 by David VanHorn

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>Well, if there is any way of getting it to work, I think that the
>transmitter expects to find a variable resistance at several of the pins of
>the buddy cable. I don't think that the trainer transmitter actually
>generates any signals, I think that the buddy cable simply reads the
>control pots.


I doubt that it's sending resistance through the cable. Most likely it's
encoded
pulsetrain output, which gets switched in or out by the master box.

>I'd bet that a PIC wouldn't have aproblem generating the PWM that is the
>actual modulating signal. If so, you could just canibalize a transmitter
>for its RF unit and feed it the signal from the PIC.


Well.. A pic could do it, but I just sent dontronics my "getting started"
code for the AVR8515 which happens to include code to generate eight servo
outputs. It would be an absolute no-brainer to hack that to output the
channels all on one pin. It has programmable position for all eight
channels, plus programmable frame rate. I was thinking along the lines of a
robot controller or some such, with the servos local to the CPU, but this
application would work as well.  It would be a very quick hack to make this
an RS-232 to servo controller, as int driven serial comms are also in the
package. Feedback would be possible, in that you could read back the current
channel settings. You have no way to know where the servos are at the other
end of the link, but you could know where you last told them to be.

It also includes a 19 bit PN generator, and stepper motor control, and a few
other little functions.
With all that, the VAST majority of the CPU time is idle.

1998\09\03@012430 by Sean Breheny

face picon face
Hi David,

At 12:05 AM 9/3/98 -0500, you wrote:
>>Well, if there is any way of getting it to work, I think that the
>>transmitter expects to find a variable resistance at several of the pins of
>>the buddy cable. I don't think that the trainer transmitter actually
>>generates any signals, I think that the buddy cable simply reads the
>>control pots.
>
>
>I doubt that it's sending resistance through the cable. Most likely it's
>encoded
>pulsetrain output, which gets switched in or out by the master box.
>

Well, I must admit to not knowing, but what I do know is that the trainer
box (the one that the student is holding) is turned off when in use, and
doesn't even need to have a battery in it. So, unless power is being sent
from the active transmitter over the cable to run the PWM electronics in
the buddy box, the only alternative that I can think of would be to have
the resistance sent over the cable, so to speak.

Sean

+--------------------------------+
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| Electrical Engineering Student |
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1998\09\03@014531 by David VanHorn

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>>I doubt that it's sending resistance through the cable. Most likely it's
>>encoded
>>pulsetrain output, which gets switched in or out by the master box.
>>
>
>Well, I must admit to not knowing, but what I do know is that the trainer
>box (the one that the student is holding) is turned off when in use, and
>doesn't even need to have a battery in it. So, unless power is being sent
>from the active transmitter over the cable to run the PWM electronics in
>the buddy box, the only alternative that I can think of would be to have
>the resistance sent over the cable, so to speak.


Assuming it's a voltage per wire, then you'd need a 10 conductor cable, at a
minimum. 8 channels, plus power and ground.  If they send the pulse train
across, then you'd only need three wires..

How many wires in your buddy cable?

1998\09\03@015204 by Sean Breheny

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Hi again David,

At 12:35 AM 9/3/98 -0500, you wrote:
>
>Assuming it's a voltage per wire, then you'd need a 10 conductor cable, at a
>minimum. 8 channels, plus power and ground.  If they send the pulse train
>across, then you'd only need three wires..
>
>How many wires in your buddy cable?
>

If I remember correctly, it is a 5-pin DIN. I am using a 4-channel RC
aircraft transmitter, so it is possible that the pin assignments are one
per channel, and then a ground. Or, 1 per channel, a n extra pin, and then
the shield is ground. Each pin in the pin-per-channel idea, would I assume
be connected to the wiper of a pot which had one end grounded and the other
end floating.

Again, I may be way off, you may be correct, but I am simply introducing
the possibility. My transmitter is an old Futaba AM system, about 7 years
old. Maybe they also do it differently now.

Sean

+--------------------------------+
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| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
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1998\09\03@020912 by David VanHorn

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>
>If I remember correctly, it is a 5-pin DIN. I am using a 4-channel RC
>aircraft transmitter, so it is possible that the pin assignments are one
>per channel, and then a ground. Or, 1 per channel, a n extra pin, and then
>the shield is ground. Each pin in the pin-per-channel idea, would I assume
>be connected to the wiper of a pot which had one end grounded and the other
>end floating.
>
>Again, I may be way off, you may be correct, but I am simply introducing
>the possibility. My transmitter is an old Futaba AM system, about 7 years
>old. Maybe they also do it differently now.


They may have a different system on each radio :) how else to get us to buy
more accessories?
Well, I'd say it's meter time.  With the more complicated radios, it's hard
to imagine that they could do servo mixing and reversing with only analog
components, I know it's possible, but YECCCHH.

You could always use a xicor EEPOT, they make them up to 6 in a package,
pure resistance output on two pins.

1998\09\03@022803 by Sean Breheny

face picon face
At 12:57 AM 9/3/98 -0500, you wrote:
>
>They may have a different system on each radio :) how else to get us to buy
>more accessories?
>Well, I'd say it's meter time.  With the more complicated radios, it's hard
>to imagine that they could do servo mixing and reversing with only analog
>components, I know it's possible, but YECCCHH.
>
>You could always use a xicor EEPOT, they make them up to 6 in a package,
>pure resistance output on two pins.
>

I wouldn't doubt it if they have changed their system several times. You
are right about it being "meter time", but unfortunately my transmitter is
back home and my meter and I am here :) I'll check when I get a chance.

I agree that it would be a MAJOR kludge to accomplish servo mixing,
nonlinear rates, etc. with all analog components, but remember, AFAIK, all
that is done in the _active_ transmitter.

Now that I think about it, one does have to check to see if the servo
reverse switches are the same on the main transmitter and on the buddy box,
so I am not sure if that indicates that it is more complex than just pots
connected to wires. Also, the dual rate switch on the the buddy box works
independently of the controls on the main box. However, reverse and dual
rate would be fairly easy to accomplish in just passive components. I
DUNNO. As you suggest, I'll check with my ohmmeter.

OTOH, isn't all this irrelevent to the original question? AFAIK, the RC car
equipment works significantly differently from the RC plane equip
(different freq., different controls, fewer channels, different box style).
Also, there are no buddy boxes for cars, are there? (what's the worst thing
that you are going to do with an RC car :), as opposed to killing
someone(possibly) with an RC plane in an 100 MPH+ dive). So, my main
original point is that it would seem to me that since there are no buddy
box capable RC car transmitters (that I know of), one would need to adapt
an RC plane box to work with the car's receiver. If you can't get an RF
module for the plane box that is the same freq. as the car's receiver, the
whole point is suddenly very academic :)

Sean

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1998\09\03@082147 by Norm Cramer

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At 12:57 AM 9/3/98 -0500, you wrote:
>>
>
>You could always use a xicor EEPOT, they make them up to 6 in a package,
>pure resistance output on two pins.
>
>

This thought had crossed my mind.  I was hoping that there might be another
simpler way to do it.  The airplane controller with the buddy interface may
be the easiest solution (not the cheapest).  I think the cheapest is to
hack into the radio control transmitter and put EEPOTS on the controls.  I
could use a PIC to provide a serial to RC interface and control it that way.

Any more ideas?

Norm

1998\09\03@090152 by Keith H

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Norm Cramer wrote:
>
> the buddy interface may be the easiest solution (not the cheapest).Indeed, if
you have no ham radio licence you'll have to
buy a transmitter anyway.
I presume this buddy interface feature adds to the cost?

> I think the cheapest is to hack into the radio control transmitter
> and put EEPOTS on the controls.

The Tx signal is Pulse-Width-Modulated FM.
The joystick resistances are used to control the width of pulses.
Analogue Txs did this directly.

You only need one output bit to drive the PWM signal
that switches the carrier between the two frequencies.
Thus you can skip the EE pots.

You can use a PIC. I have an article about a commercial product
that used an H8. If you use a PC you won't want it to
be driving the PWM all the time, in which case the EE pots
would be the better bet.

1998\09\03@093708 by ken

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The cable is a sort of "command override".  The buddy box is the actual
transmitter in use, and requires that it be crystalled to match the
student's transmitter.  The trainer holds a "dead-man" switch to enable the
student to operate.  When the student gets into trouble, the trainer
releases the switch and the student transmitter shuts down.

The process at work is probably a detectable voltage drop or change in
resistance, but there is no data sent over the cable.  It's just a switch.

Ken

{Original Message removed}

1998\09\03@093852 by ken

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Well, it's academic, then.  I've used a Airtronics 8ch helicopter
transmitter with a car-freq crystal in it for many years to control things
from sailboats to model tanks :)

Ken

{Original Message removed}

1998\09\03@110611 by stenulson

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Hi-

Just signed onto this list - missed the earlier discussion; (will
examine the signal to noise ratio to see if I can stay on this list-
little useful in the first ~100 messages... ? )

Look at the JR RC systems; they use a single pair wire for the buddy
cord, with an 1/8" plug on either end; note that also, in buddy box
operations, all trims must be matched on both master & slave, and all
servo reversing switches must match on both...

(Done a lot of RC flying - have Airtronics, Futaba, JR systems on hand)

Bruce

1998\09\03@111030 by stenulson

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David VanHorn wrote:

>
> How many wires in your buddy cable?

Correction on my note on the JR system; just went to look; it's a 3
wire, as you noted; mini stereo headphone type plug on either end...

Bruce

1998\09\03@122745 by Peter L. Peres

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There are 3 kinds of master/slave systems on RC Txes that I know of:

1. Dry pots. The pots are read out through a wire each by the master
transmitter, plus GND. Slave has power off while doing this. This is what
Sean has indicated. Often has a 5 pin DIN (old system).

2. PWM rules. The slave has power off but receives power from the master
through the cable. Only the PWM part of the slave works, the Tx is off.
Often has 5 pin DIN.

3. uC to uC. The computers in the two Txs talk over the cable using a
proprietary protocol. Almost never uses DIN 5 pin, excepting some older
semi 'home-made' designs based on 8051 uCs.

hope this helps,

Peter

1998\09\03@124957 by shadedemon

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All modern systems simply route the gate signal from the
first tranmitter to the second, instead of feeding the
first's transmitter module.  10 one to two ms pulses in the
case of my PCM 10.  Servo reversing having to match has
nothing to do with it being analog.  If the plane/heli is
set to go UP when the signal is shorter, then my signal
better be shorter when I push up or your heli's gonna go
down.  Other than that, my mixing works when I'm in control,
and your's works when your in control.  If my mixing is
doing something you don't like you let go of the switch.
All the switch does is pick whether my pulse train or yours
is going through your transmitter module.  NO, they do not
have to be the same frequency, because ONLY your transmitter
module is working, and we're flying YOUR plane.  Almost no
one would be able to use a buddy box otherwise because you
don't want to have the same freq's for normal flying.  The
other pins on the trainer cord that are used are to turn off
the first tranmitters output.
 For controlling the car, just buy a cheap used JR
transmitter.  Since the beginning of time they've had a
seperate transmitter module in the back with a connector
with 6 or 7 pins.  (The module from my 1981 apollo heli
plugged straight into my 90's PCM 10 and works well.)  One
of these is a pulse train to gate the RF for all the
servos.  INSERT your pic here.  What you pump out here will
control the servos.  If you need to then read the
transmitter coming in, modify the signals as needed, and put
the result out into the module.  Not that hard.  If you use
a non-JR transmitter without seperate module it is still
easiest to find this signal before it enters the RF and
intercept it.  It is probably not TTL-CMOS so buffer
accordingly.
 Sorry for the long post but you guys are making it a lot
harder than it is talking about hacking in eepots and
crap..  Even for just a couple of channels it's still easier
to get into it.
 Just checked and it's five pins to the JR module.  Power,
ground, signal out, feedback for the signal meter, and
probably a different power.  Shouldn't be hard to find and
tap the signal.  Should also be about the same as what comes
out the DSC / trainer jack..

Alan

1998\09\03@125630 by Ken

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My earlier post was slightly erroneous.  The setup I was describing was #3
below.  It seems that the setup in question is probably #2.

My system uses two fully-featured transmitters, either can be master or
slave.  Whoever is designated as master has to hold a switch down to turn of
his radio transmitter, and let it up to turn off the other transmitter.  The
protocol is complex, and is a frame-based serial protocol.

Ken

{Original Message removed}

1998\09\03@125733 by David VanHorn

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>OTOH, isn't all this irrelevent to the original question? AFAIK, the RC car
>equipment works significantly differently from the RC plane equip
>(different freq., different controls, fewer channels, different box style).

Only if you use a dedicated car radio. I've always used sticks for
everything.
Plane radios can be re-rocked to ground frequencies, some are even
synthesized and don't need new rocks.

If you can't get an RF
>module for the plane box that is the same freq. as the car's receiver, the
>whole point is suddenly very academic :)


You can. unless he's talking about the 49/27 mhz stuff.  Still, that may be
even easier, I've seen them using standard pulsecodes, so it should be easy
to find the point that says "cut here to insert external pulses" :)

1998\09\03@131102 by David VanHorn

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>>
>> How many wires in your buddy cable?
>
>Correction on my note on the JR system; just went to look; it's a 3
>wire, as you noted; mini stereo headphone type plug on either end...
>
>Bruce

I'd submit that this looks an awful lot like a cable that would pass servo
pulses, with ground and maybe a signal to disable the TX on the student box.
I've got JR gear here, but no buddy cable, I never thought to dig mine up
and look at it.

1998\09\03@133213 by David VanHorn

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>  Sorry for the long post but you guys are making it a lot
>harder than it is talking about hacking in eepots and
>crap..  Even for just a couple of channels it's still easier
>to get into it.


Ok, that's pretty much what I expected. I only suggested the EEPOTs as a
workaround if the interface was sending individual voltages through the
cable, which didn't seem to me like a very workable method, but others have
asserted that they have, or know of gear that works that way.

Generating the pulse train is easy, On the AVR, I have a 16 bit timer loaded
with a base value for 1mS, plus the servo width byte which adds an
additional 0-1mS. I set the active channel's bit high, and start the timer.
The timer ISR sets all channel bits to zero, and advances the active
channel. This gives me 4uS resolution, without blowing the CPU away in
nop-loops.

Init loads a frame rate byte with a frame constant, usually about 20mS, and
there is a control byte in RAM for each channel. (0-255)

The servo routine checks if we are on servo 1, and if so, it waits till the
frame rate byte hits zero before proceeding. All other channels ignore the
frame byte, so they are sent directly after the first channel. The frame
rate byte is dec'd to zero by the 1mS opsys ISR. Once it sees zero, we set
servo 1 active, and reload the frame rate byte.   You would need to add a
pulse delay so that there is some fixed space between servo pulses, since in
your application they are all output on the same pin.

http://www.dontronics.com/8515.html has the source for the AVR
implementation, and I think it wouldn't be hard to implement it on a pic or
whatever else.

1998\09\03@133429 by Andy Kunz

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>Well, if there is any way of getting it to work, I think that the
>transmitter expects to find a variable resistance at several of the pins of
>the buddy cable. I don't think that the trainer transmitter actually
>generates any signals, I think that the buddy cable simply reads the
>control pots.

No, it carries the data in the demodulated format so that the RF deck on
the other transmitter can put it on the airwaves.

>I'm sure someone else on the list can shed more light on this. Perhaps Andy
>Kunz?

Why me?

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\03@133433 by Andy Kunz

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>Well, I must admit to not knowing, but what I do know is that the trainer
>box (the one that the student is holding) is turned off when in use, and
>doesn't even need to have a battery in it. So, unless power is being sent
>from the active transmitter over the cable to run the PWM electronics in
>the buddy box, the only alternative that I can think of would be to have
>the resistance sent over the cable, so to speak.

No, power is available if needed.  It depends on the brand.  Earlier
comments are based on Futaba and what I did for FMA, although they haven't
manufactured that (yet).

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\03@133438 by Andy Kunz

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>Again, I may be way off, you may be correct, but I am simply introducing
>the possibility. My transmitter is an old Futaba AM system, about 7 years
>old. Maybe they also do it differently now.

Hey, join the club!  I was wrong once, too.  I thought I had made a
mistake, but I hadn't <G>

Futaba has done it this way for ages.

Say, you aren't using that illegal WIDEBAND transmitter these days, are you!

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\03@133443 by Andy Kunz

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>OTOH, isn't all this irrelevent to the original question? AFAIK, the RC car
>equipment works significantly differently from the RC plane equip
>(different freq., different controls, fewer channels, different box style).

Actually, most of them are just limited by what they put in the box.
Futaba might be different due to volume, but basically they only pay for
one development.

>box capable RC car transmitters (that I know of), one would need to adapt
>an RC plane box to work with the car's receiver. If you can't get an RF
>module for the plane box that is the same freq. as the car's receiver, the
>whole point is suddenly very academic :)

You can kludge one in very easily.  A little probing with a scope and
you'll find the traces to cut.  You can also figure it out by comparing a
Conquest to a Magnum directly.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\03@133448 by Andy Kunz

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>The Tx signal is Pulse-Width-Modulated FM.

No, they are Pulse Position Modulated.  The PWM is a function of the
receiver shift register.

Why not contact me offline and I might be able to share some pointers on
this whole deal.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\03@140544 by Sean Breheny

face picon face
Hi Andy,

At 11:06 AM 9/3/98 -0400, you wrote:
>
>No, it carries the data in the demodulated format so that the RF deck on
>the other transmitter can put it on the airwaves.

Do they all work this way? If so, why did any ever have 5 pins?

>
>>I'm sure someone else on the list can shed more light on this. Perhaps Andy
>>Kunz?
>
>Why me?
>

Because I've seen you answer lots of RC questions before, and you used to
work for (own?) a company that had alot to do with RC (your old signature
line, "keep the wet side down" etc.)

>Andy
>
>
>==================================================================
>Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
>==================================================================
>
+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
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1998\09\03@140551 by Sean Breheny

face picon face
At 11:07 AM 9/3/98 -0400, you wrote:
>
>No, power is available if needed.  It depends on the brand.  Earlier
>comments are based on Futaba and what I did for FMA, although they haven't
>manufactured that (yet).

So, power is usually fed to the trainer (non-transmitting) box?

>
>Andy
>
>
>==================================================================
>Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
>==================================================================
>
+--------------------------------+
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| Electrical Engineering Student |
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1998\09\03@140759 by Sean Breheny

face picon face
At 11:09 AM 9/3/98 -0400, you wrote:
>
>Hey, join the club!  I was wrong once, too.  I thought I had made a
>mistake, but I hadn't <G>

That's about as recursive as GNU's Not Unix <G>

>
>Futaba has done it this way for ages.

"this way"= sending PPM data?

>
>Say, you aren't using that illegal WIDEBAND transmitter these days, are you!
>

That's a good question. I'm not sure of the exact age of my transmitter,
but it DOES have an AMA gold sticker on the bottom, so I think its
narrowband. Put it this way, it is channel 54, and conforms to the standard
channel allocation system in use at my flying club.

>Andy
>
>
>==================================================================
>Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
>==================================================================
>
+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
@spam@shb7KILLspamspamcornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\09\03@144640 by Quentin

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Andy Kunz wrote:

> No, power is available if needed.  It depends on the brand.  Earlier
> comments are based on Futaba and what I did for FMA, although they haven't
> manufactured that (yet).
>
> Andy
>
Aha! So you the one who designed FMA's TX?
How about some inside info on what functions it got?
hehe

Quentin

1998\09\03@170527 by Andy Kunz

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>Do they all work this way? If so, why did any ever have 5 pins?

There are several methods.  I don't have the schematic for my FMA
transmitter here, but it had that.  I believe it was pwr, gnd, switch, and
data.

>Because I've seen you answer lots of RC questions before, and you used to
>work for (own?) a company that had alot to do with RC (your old signature
>line, "keep the wet side down" etc.)

Oh, I worked for FMA Direct for a while, still do stuff for SubTech, and
still sell my own R/C stuff.

I was kidding - as in the persecuted whine, "why [does it always happen to]
me?"

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\03@170529 by Andy Kunz

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>"this way"= sending PPM data?

Yes.

>That's a good question. I'm not sure of the exact age of my transmitter,
>but it DOES have an AMA gold sticker on the bottom, so I think its
>narrowband. Put it this way, it is channel 54, and conforms to the standard
>channel allocation system in use at my flying club.

Gold sticker doesn't mean anything anymore.  You should have it checked at
an AMA Licensed Station.  The guy locally who does this is Rock Leone.  He
goes to a lot of the trade shows, I understand.  Met him at WRAMS a couple
times in a booth.

The guys in our club use him because he's local and cheap - $25 will
certify your tx as narrowband, gets a narrowband sticker on it instead of
the AMA Gold.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\03@170531 by Andy Kunz

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>Aha! So you the one who designed FMA's TX?

I designed the original one, PIC-based.  The schematic I did on a napkin in
their office as I was heading home one night and we were all parting.  I
cleaned it up a bit in a CAD package and sent that down, next time I saw it
Tim had a gorgeous schematic to mil-spec stds in Autocad.  Fred had the
ideas for the case and the programming method (which is the same one Futaba
used in the 3PDF, developed independently).  The idea of programming it was
"wiggle the channel you want to program."  Very intuitive.

After we parted ways (unfavorably, sad to say) I understand they bought the
rights to the Airtronics tx - I forget which - and were looking for a new
case.  From the grapevine I've heard horror stories about tooling the tx
case.  It's a shame - I was putting finishing touches on the code when they
cancelled the project.  They were > < that close to having it!

>How about some inside info on what functions it got?

Mine had 10 model memory (artificially set <G>), 16 channel-capable output,
20 channel input (trims were counted as channels internally and mixed in to
derive commands on channels 1-4, so 20 channels - 4 trims = 16 output),
full mixing, dual rates, exponential wasn't done yet.  It included support
for a synthesized RF deck (PLL) as well.  All in PIC assembly, and the chip
was VERY full.

I learned a lot in the process.  After we parted, I ended up rewriting it
in HiTech C.  I moved to a '76/77 part and had all kinds of room for new
features, and may someday go ahead and market this myself.  I work with an
RF engineer who is doing prototyping on the synthesized RF deck.  Maybe
we'll sell it to somebody and get rich <G>.  It's based on the schematic I
drew on the napkin, though improved in areas that I found were problems
with the original one.

I have no idea what FMA is doing nowadays, or if they are still planning to
do a tx.  When I was working for them, they had this perpetual "6 months to
go" policy because they couldn't work with the mech engr close enough.

I use their receivers almost exclusively - they are EXCELLENT!  I have the
S-200 servo in a lot of my stuff, too.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\09\05@130555 by Peter L. Peres

picon face
On Thu, 3 Sep 1998, Norm Cramer wrote:

> be the easiest solution (not the cheapest).  I think the cheapest is to
> hack into the radio control transmitter and put EEPOTS on the controls.  I
> could use a PIC to provide a serial to RC interface and control it that way.
>
> Any more ideas?

imho an EEPOT is overkill for this. Radio pots are almost always
referenced to GND or Vdd. All you need is an 8 bit PWM converter followed
by a low pass filter driving a JFET in the well-known linearized
potentiometer configuration. In this case, due to the high Z of the JFET,
a very simple RC smoothing unit will do (probably 2 cells). A PIC can be
programmed easily to output PWM even if it has no internal support for
PWM.

my 2 bits

Peter

1998\09\05@154221 by Peter L. Peres

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On Thu, 3 Sep 1998, Ken wrote:

> My system uses two fully-featured transmitters, either can be master or
> slave.  Whoever is designated as master has to hold a switch down to turn of
> his radio transmitter, and let it up to turn off the other transmitter.  The
> protocol is complex, and is a frame-based serial protocol.

If you are SURE about this then borrow a DSO and perform some of what is
sometimes called 'hacking'. There are only 2 kinds of protocols in wide
use for this kind of application:

1. Dumb: All state data is encoded in a large packet, and sent. Packets
are the same size, always. May be SPI or RS232 on TTL levels. Pay
attention to the number of bits in ALL packets, some 'far-sighted' designs
use the 9th bit available with some UARTs for extensions (such as
slave/master addressing).

2. Smart: A full state frame is transmitted once a second or so, meanwhile
nothing if no change in state, else a code with the item that has changed
vs. the previous data. This is less likely to use the 9th bit and may be a
bit-banging protocol with less than 8 bits per word for some messages.

3. You may still have been fooled by the PWM data travelling in both
directions to allow either Tx to become a master. To check this, examine
the cable. It should not be a 1:1 straight through cable if this is true
and the Txs are identical (some pins may be reversed for the double PWM
system), at least 2 in fact, probably 4.

hope this helps,

Peter

1998\09\05@172422 by David VanHorn

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I just looked at my local hobby shop for a trainer cable for my JR radio.
It's two conductors. A MONO 1/8 inch plug.

There appear to be a large number of systems!

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