Conference vmszoo::rc

    The symptom you describe smacks of motor interference.
    
    You may not have had the problem before, but answer this.  Do you
    clean the motor on a regular basis?  Do the brushes need changed?
    Motor Maintenace is critical, especially in the dirty offroad types.
    
    I cleaned my motor after every race or about 1 time a week in cleaner
    environments.  The fact that you run the motor cases the brushes
    to wear and creates carbon dust inside the motor.
    
    I suggest, 1) remove, inspect and clean the motor.  Use a quality
    motor cleaner (I like Trinity brand).  Change brushes if needed
    (don't forget breakin) and reassemble motor.  2) install caps on
    the motor.  This is especially important if you're using an Electronic
    Speed Controller.
    
    G'luck,
    Chris
    dtn 445-6577

The strange thing about that one is that its only one servo;
because you didn't mention the other one I assume that its
function is ok.  Is the new servo located very near a motor or
the wires carrying current to the motor?  Sometimes this causes a
problem by inducing noise into the servo leads or directly
into its components -- that feedback loop inside the servo is
very delicately balanced for sensitivity.

The cure is either to move the wires or the servo, or put a cap
on the motor (which is what I would try first).   This happens a
lot in electric planes because of the in-line nature of the
installations -- the motor on/off servo is by nature close to the
motor battery leads, and to its own input from the Rx. 

The motor noise may not have been critical before because of the
location of the components.

Check for any metal-metal contacts, they're deadly, but would
cause general interference to both servos, not whats happening in
your case.  Still, an ounce of prevention...

Funny this should come up, I'm rebuilding an electric model and
am now installing the motor on/off servo   I use a small servo
with a microswitch -- one of these days I'll build a solid state
on/off controller, they're simple enough.

I've learned a lot about the installation from the first time I
did it and am redoing all the wiring and connectors.  Its a real
stinker getting the stiff motor battery wires down into place
inside a delicate balsa fuse.  I'm thinking of installing bus
bars along either side of the fuse and making the connections to
them at each end with the good ol' Deans 4-pin connectors.  And
its only a ferrite .035 with about 7 amps draw: you folks with
the larger motors have to deal with 15 amps and up in your
connections! 

    Just a short comment related to .1 where the radio mentioned is a 7
    channel FM.  If this isn't a boat radio (I've never seen a 7 channel
    FM car radio) It should have a red flag at the end of the antenna
    labelled AIRCRAFT USE ONLY, and it shouldn't be in a car !!  Myabe
    the radio knows its being missused, and is simply rebelling against
    authority.

    re: .1
    
    I don't have normal R/C motors in the vehicle, it's been converted to
    some motors from daisy wheel printers that have 4 brushes each and put
    out lots of torque, but turn relatively slowly.  When I was installing
    them, I checked them out and they seemed OK, and I wouldn't even know
    where to find replacement brushes anyway... The case of the motor
    is sealed, so there isn't any dirt getting in there.
    
    They only draw 3 amps max from the 12 volt supply, so I doubt it's a
    current problem, though it could be noise, I'll try caps tonite (what
    value is reasonable, I assume I should use ceramic disc caps?). 
    
    Willie

    re: .2
    
    The really strange thing is that it's only one servo and it's the
    original steering servo, not the new one!  Everything else is mounted
    just where it was before the conversion.  In fact the new servo
    has the motor leds running right next to it (practically wrapped
    around it) while the original servo is pretty far away from anything
    else.
    
    You mentioned metal to metal contact, does this really make that
    much of a difference?  I replaced the old 'servo tray' with a piece
    of aluminum, but that was a while back.  Should I tie the aluminum
    to the (-) supply?
    
    Willie
    

    When I read your problem I immediately had the same thoughts as
    mentioned in the first reply (i.e. clean the motor). But since your
    using different types of motors who knows?  I would try the caps
    but don't use electrolytics (cannot be reversed).  You want ceramic
    caps with good high frequency characteristics.  They are normally
    mounted directly on the motor.
    
    Even if the caps don't work I would still suspect the motors based
    on my own experiences and the experiences of others.
    
    Todd
    

    re: .3
    
    Do you have any idea how hard it is to get a 7 channel radio for
    car frequencies?  Do you have any idea the strange looks you get
    when you ask for one?  Can you guess at the response when you explain
    that you need:
    
    1)	throttle
    2)	front steer
    3)	rear steer
    4)	camera pan
    5)	camera tilt
    6)	plow blade position
    7)	RFU
    
    Yes, you have caught me out, but I do have a complete set of
    transmitter and reciever modules on order, and as soon as Futaba
    builds them for me, I'll be 'legal'.  In the meantime, I leave the
    transmitter antenna all the way down and only drive around inside
    my apartment (it's too wet and snowy outside).
    
    While we are on the subject of what's legal, are you allowed to
    have a transmitter module on the vehicle sending data back to the
    operator?  Once I get my new modules I'm planning to have the old
    aircraft frequency modules rebuilt for car frequencies for sending
    data the other way.  Will a transmitter on another channel in the
    same band in close proximity to a reciver cause problems?
    
    Willie
    

On the motor noise caps: You know, I never really noticed what it
was.  The cap on my Astro is a little teeny bugger about 1/4 inch
diameter -- does .002 sound about right?

    I was successful with the (3) .1 uF and (1) .47 uF as follows;
    
    one .1 between the motor case and each brush (2).
    one .1 between the brushes
    and with the ESC use an additional .47 at the power connector as
    close to the ESC as possible
    
    This was the arrangement recommended by NOVAK (they make ESC's)
    
    Chris
    
    

    Hmm, since each motor has 4 brushes, does that mean I need 8 caps
    brush-to-case, 8 caps brush-to-brush, in addition to the ones on
    the ESC?  Why wouldn't ESCs have bypass caps in them anyway?
    
    Oh, well, I'm nome now, so it's time to start trying things....
    
    Thanks for all the response!
    
    Willie

    re -.1
    
    I don't know.  I had a lot of problems until I used that setup.
    
    Keep in mind that those values are for standard 540 type motors.
    
    keep trying until you find a combo that works, and be careful not
    to over do it with the caps.
    
    Chris

    Close proximity transmitters on adjacent or near adjacent frequencies
    will probably cause you no end of pain and frustration (not to mention
    crashing).  Aircraft modelers are constantly on the lookout for
    potential interference problems, which include, but are not necessarily
    limited to, adjacent channel interference, Third Order Intermodulation
    interference (also known as 3IM), and simple RFI/EMI from non-RC
    related sources.  For you, however, the problems caused by interference
    are minimized by the fact that you can always just go and get your
    car if it runs away, unlike airplane flyers, who typically have
    to learn to duck.  Just try different frequencies until you get
    two that don't conflict.

    I thought it was my computers (none of them meet any FCC regs, as I
    built a few of them from scratch), but I just took it for a walk around
    the building and it still happens.  There is some kind of interference.
    cuz I can watch the vehicle go berzerk when the transmitter isn't
    powered up, so maybe I'll wait until my new tx/rx modules get here and
    see if the problem goes away.  I did find one way to solve the problem,
    hook up a DVM to the BEC output of the ESC!  In fact, hook up just the
    DVM leads to the output and the problem goes away....
    
    Is there any easier way to find a clear channel than spending $40
    and 4-6 weeks per try?
    
    Willie 

    Willie,
    
    Turning off the transmitter is not a valid check for interference...
    without the reference pulse from the transmitter, the receiver
    _will_ [see, I'm learning :-) ] go nutz hunting for some reference
    to lock onto.  I don't pretend to understand the technical reasons
    for this but I know that almost anything, e.g. fluorescent lights,
    power tools, even mechanical metal-to-metal noise will bug the re-
    ceiver/servos when the transmitter signal is absent.
    
    Adios amigo,	Al

    Al,
    
    Gosh, an entire reply without a single quote, I'm proud of you! :+)  I
    found the problem yesterday, it was an assembler error and was real
    obvious once I finally saw it.  See, I had wedged the R/C reciever in
    between the TV transmitter and the speed controller, where it was sure
    to pick up the maximum amount of intereference from both....  Moving it
    back behind the TV camera solved the problem, and now I don't even get
    the 'transmitter off' berserk_servos problem unless I get my hand close
    to the R/C reciever antenna.  I still think it's all magic!
    
    Willie

> hook up a DVM to the BEC output of the ESC!  In fact, hook up just the

Willie; what's the BEC output of the ESC???  Glad to see you
found the problem.  I wasn't reading this note too carefully and
didn't know there was a TV signal in there.  Of course, the video
signal, has harmonics right there in the passband of the
receiver.  Any explaination for only one servo being effected?

    WIllie,
    	You will definately have interference problems if you try to
    put an RC transmitter near the receiver even if you put them on
    different channels.  The transmitter will overload the receiver
    if the antennas are close, and swamp out the desired signal.  Your
    only chance of success would be to separate the antennas as much
    as possible and maybe lower the output power of the transmitter
    in the car to prevent overpowering the received signal.  I am not
    sure whether it is legal to transmitt from a vehicle on RC frequencies.
    
    CHarlie
    

    >Willie; what's the BEC output of the ESC???
    
    Sorry, too many TLAs!  The Electronic Speed Controller has a Battery
    Eliminator Circuit, so you don't need a reciever/servo battery in
    the vehicle.  I suspected that the added load of the additional
    servo might have been too much for it, especially since I'm running
    it on the equivalent of a 10 cell nicad battery pack.  No idea at
    all why only that one servo was effected, but the problem is gone
    (for now?) and I'll wait for it to come back till I worry about
    it too much more.
    
    Oh, well, it mystifies the neighbors properly, having a vehicle
    driving around with no visible operator!  :+)
    
    Willie

    If the problem goes away when you hook a DVM to the BEC of the ESC,
    then put a SCC (Small Ceramic Capacitor) between BEC and GND and you
    should be in good shape. 
    
    (translation: You apply a mostly-capacitive load when you hook your
    meter leads to the battery-eliminator power output.  Since this makes
    the problem go away, putting a Small Ceramic Capacitor there will do
    the equivalent.  Small Capacitors can act like noise filters, eh?)