From: hutto@SMTC.engr.scarolina.edu (Brent Hutto)
Subject: Re: RC10T steering problem
Reply-To: hutto@smtc.engr.scarolina.edu
Organization: NIST Southeast Manufacturing Technology Center
Date: Wed, 14 Oct 92 22:30:45 GMT

In article <Bw4ICB.L08@ux1.cso.uiuc.edu>, kmiller@ux1.cso.uiuc.edu (miller kendall w) writes:
>I just got a RC 10 team (aluminium) car and I love it, but I am having one
>major problem.  First, my steering doesn't auto center right when I release
>the controler-- if I release it from the right, it ends up a little pointing
>right.  From the left, a little left, etc.  This makes it, as you can imagine
>very difficult to control at speed (I drive on concrete/dirt) To reduce
>this, I moved the rod down on my servo so that it was attatched to a lower
>radius.  while this reduced it did not eliminate the afore mentioned problem,
>and it increased my turning radius because the servo only pivots thru
>about 100 degrees of it's travel. 
>
>I am using the Futaba Magnum Sport remote control,
>1) how can I eliminate or reduce to a minimum the centering problem, and
>2) how can I do #1 and at the same time keep a good turning radius?
>
>Any things you could come up with would be good.  I have tried both the 
>middle and outer position on the RC-10 servo saver, in combination with a
>couple places on my servo.
>
>--Ken

    0) Turn the radio and car on, place the car on a surface similar to what
    you run it on, mash the front end down to make the front wheels bite on
    the surface and work the steering wheel back and forth back and forth.
    This simulates the actual steering during the running of the car.

    1) If you are using "servo tape" to hold the servo to the chassis, it can
    let the servo case move relative to the chassis.  Just a little of this
    type of motion can cause steering problems.  If you see any flexing of the
    tape, bolt the servo down using nylon mounts.

    2) If the servo is secure to the chassis, look to see if the "servo saver"
    arrangement built in to the Team Car steering mechanism is flexing under
    load. That's actually a rhetorical question, the built-in steering
    mechanism always has slop in it.  Use a small nylon wire-tie around the
    built-in so-called servo saver to disable it.  Buy a Kimbrough servo
    saver and put it directly on the servo.

    3A) Take the servo loose from the steering and pick up the car.  With no
    servo, you should be able to start with the front wheels at one extreme
    and just barely tap them with your hand to make them swing all the way
    to the other extreme. If they don't move that freely, there is some
    binding in a linkage or something.  You must fix that in order for the
    servo to have enough oomph to accurately center the wheels, which brings
    us to...

    3B) You didn't say what sort of servo you have. If it is an S148, then
    the problem is most likely slop or binding of some sort.  If it is a
    S132, the problem may be insufficient strength (torque) from the servo.
    Other denizens of the net will tell you that a S132 is plenty strong
    for a 2WD car.  I don't think it is.  With an S148, the wheels must move
    pretty much freely with no binding.  For an S132 to work at all, there
    can be *absolutely no binding* anywhere in the steering. One other note
    about the S148.  It does not have ball bearings and therefore can't
    possibly center accurately.  However, if it is new and the nylon bushing
    isn't worn out, it is capable of centering more closely than you're
    likely to notice in an off-road car.

    4) A very severe case of the problem you stated is the symptom of a
    cracked gear in the servo.  If this is the case, you won't be able to
    control the car at all at speed, it will wander everywhere.  To tell
    if you have a cracked gear, either open up the case and look or take
    the servo off the car and move the shaft back and forth and see if it
    has smooth, steady resistance to turning of if it has a vague, broken
    feel to it.

    That's all that pops into mind right now.  Check these things out and
    let us know what you find.  BTW, the suggestions about eliminating slop
    and bind are worthwhile whether you have another problem causing your
    symptoms or not.  You can only drive as well as your car will steer.
    If you take a little care to avoid sloppiness and binding, the car will
    steer better than you can for quite a while ;-)

-------------------------------
Brent Hutto
hutto@SMTC.engr.scarolina.edu