servo question

[JOddino]

I've heard others say how they can feel the improvement in loops when they
use digitals on ailerons.  Sounds like a case for flaperons coupled to
elevator.
Jim
----- Original Message ----- 
From: "Troy Newman" <troy_newman at msn.com>
To: <discussion at nsrca.org>
Sent: Sunday, August 03, 2003 2:25 PM
Subject: Re: servo question


> Very good stuff....
>
>
> I learned a little too....
>
> I subtrim the servos to get the pushrods square to the arms....This is the
> way I was taught to do it.
>
> The built expo thing will be radically changed when using the radios expo
> function so I can see that one going away for all practical purposes...
>
> But yes with the servo arms square to the pushrod....This is putting the
> neutral point in the worst place on the servos rotation for power. You are
> giving the force applied from the other side the max moment arm to push
the
> servo against its will....But at neutral control throw how much force is
> being applied to the servo.....very little would be my guess compared to
> when the servo is deflecting.
>
> The one time that ailerons for example are neutral and have huge forces is
> in a pull or push. The forces of pushing or pulling a corner even a wide
> radius will cause the ailerons to deflect....This is where the digital
> servos EXCEL...they hold the ailerons tighter to the neutral position by
the
> fact of their increased holding power....So your loop segments are
> straighter...because as the ailerons blow-back the question is are they
> going to move the same amount....?
>
> The answer to that is probably not....and you know they are "trimmed" at
the
> neutral position. So if you can just hold them at neutral what ever it
takes
> it will help the looping segments.....
>
> Yes this power of the servo comes at a little cost the battery packs need
to
> be a little larger...The power in the servo comes from somewhere and its
the
> battery pack.
>
> These forces in flight are another reason to have very stiff control
> surfaces and linkages.....If the aileron can flex they will...An no matter
> how good of servo you install it won't help...Wood varies and the two
> ailerons if allowed excessive flex will not flex the same as each
other....
> so minimize the flexing by making the surfaces as rigid as possible...
>
> You will get more consistency in your flying....Just like running a
voltage
> regulator...consistent voltage means same power and speed on the servos
> throughout the flight and from flight to flight....The name of our game is
> consistency...If the model flies the same everytime then you can really
> practice and learn to fly the maneuvers....If the model is changing under
> different conditions all the time,  all your practice time is spent
learning
> the model and it faults and flaws under that days conditions.....Makes the
> advancement of your flying skills take even more fuel burning than needed.
>
> A quote from a Famous Pattern flyer....."Make the model do the
work....tune
> the model so that it does it for you and makes the flying as easy as
> possible."
>
> TN
> ----- Original Message ----- 
> From: "JOddino" <JOddino at socal.rr.com>
> To: <discussion at nsrca.org>
> Sent: Sunday, August 03, 2003 4:11 PM
> Subject: Re: servo question
>
>
> > Hi Troy,
> > The reason I asked this question is that I heard a guy claiming his
> neutrals
> > were more positive if the servo horn was perpendicular to the pushrod at
> > neutral.  I see you recognize the system becomes stiffer the closer you
> get
> > to the servo arm being parallel to the pushrod.  That is why we used 180
> > degree servos on landing gear.  So the servo arm perpendicular to the
> > pushrod doesn't improve holding power at neutral.
> >
> > In the old days before computer radios we used to offset the servo
> neutrals
> > on purpose to get more up than down ailerons for example.  Now we can
set
> it
> > anywhere we want so the angle isn't critical from that point.
> >
> > As far as expo (non-linearities) caused by linkages, it is insignificant
> > (with reasonable linkages) compared to the expo we add.  Forget about
> linear
> > distances, look at angles.  The change in lift is a function of the
angle
> of
> > attack, an angle.  The angle of attack is a function of the surface
> > deflection, an angle.  The surface deflection is a function of the servo
> > rotation, an angle.  Therefore the airplane responds to the servo angle
> not
> > the linear change of pushrod distance.  It takes a special linkage to
get
> a
> > linear relationship between servo angle and control surface angle but
even
> a
> > setup that looks bad really isn't too bad after we adjust end points and
> add
> > expo.  It seems to me it is more important to make sure the angles and
> push
> > rod lengths are the same (speaking of two elevator servos or two servos
> > coupled to one surface)  rather than worrying about a non-linearity that
> is
> > difficult to measure.  It seems to me it is much easier to set the
servos
> > arms  90 degrees to the case than to try to figure out the angle that
will
> > make them 90 degrees to the pushrod.  In fact I'm not sure how you'd do
it
> > other than by cutting and trying.  I normally strive for both,
> perpendicular
> > to the case and the pushrod. However, I'm building a new plane with the
> > servos on their sides in the wing and stab where I can't have both so
I'll
> > have to look at this a little closer.  I'm still betting it is
> > insignificant.
> > Jim
> > ----- Original Message ----- 
> > From: "Troy Newman" <troy_newman at msn.com>
> > To: <discussion at nsrca.org>
> > Sent: Friday, August 01, 2003 5:02 PM
> > Subject: Re: servo question
> >
> >
> > > Oh come on Jim....
> > >
> > > For the rest of the guys...The servo moves in a  rotational
motion...So
> > the
> > > linear distance traveled by a pushrod attached to the arm or wheel
will
> be
> > > greatest right off of center and will reduce the amount of linear
travel
> > of
> > > the rod as it rotates around. A linkage not setup this will have a
funny
> > > expo like knee in it...But it will be as the arm passes through the
> square
> > > position so it would be like adding expo on only one side of the
servos
> > > travel...and reverse expo on the other side of travel.......
> > >
> > > Also it could be way up high on the travel of in a funny middle
> spot...and
> > > you will get more throw one side than the other....
> > >
> > > This sq to the pushrod also gives the servo best mechanical advantage
> > > through the range...as the servo gets to the endpoints say full travel
> up
> > > elevator..the highest force is being applied the surface...and the
servo
> > arm
> > > is rotated in such a way to reduce the moment arm on the servo by the
> > > pushrod pushing back.....The arm travels in an arc and the arm gets
> closer
> > > to the center of the servo as it rotates off of "center"....This
moment
> > arm
> > > is leverage for the pushrod to pushback on the servo.....So if you
> reduce
> > > this distance when the forces are higher then it will make the servo
> have
> > a
> > > mechanically better shot and holding its position.
> > >
> > > did I get it right Jim?
> > > anything to add Jim?...I'm by far not the expert on this stuff...
> > >
> > > Ok Still TMI....
> > >
> > > TN
> > >
> > >
> > >
> > >
> >
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> >
> >
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