servo question

[Troy Newman]

Yes control surface flexing is an important issue also. They may be flexing
too much on your plane?
They need to be stiff.....and how stiff is stiff enough? Well In my opinion
if they is any movement its too much....but in reality this can't be
achieved...weight issues....building issues....and material issues....

I have seen some guys stick light balsa false ribs in the aileron area and
then when they get laminated top and bottom with the sheeting its
stiffer...I have also heard of guys stick CF laminates in the Aileron...I
have also though of using small CF tubes or solid rods like the 0.070" CF
rods to stiffen the aileron....

Then there is the control horn hard point...The dowel that most of us
use...needs to be into balsa...maybe a large balsa "pad" that is under the
sheeting...Or better yet instead of the dowel maybe the thin Ply plates top
and bottom are best....and having them very oversized like 1.5-2" wide..this
will help spread the load and reduce the flex in this part of the
aileron....Next where is the horn in relation to the rest of the
aileron...Is it very inboard say 2 inches from the root end of the aileron
or is out near the centroid of the aileron...notice I didn't say middle of
the length!

Carry that further and the grain choice of the sheeting for the aileron area
is important...don't want the really soft spongy stuff.....And maybe even
the grain direction can play a critical role here also....

Lots of stuff to consider to make a model better!

Do all of these things play a role in how a model flies sure they do...how
much effect they have is another story...They all have some effect the
question is it worth fixing or not!

TN
----- Original Message ----- 
From: "RC Steve Sterling" <rcsteve at tcrcm.org>
To: <discussion at nsrca.org>
Sent: Sunday, August 03, 2003 6:21 PM
Subject: RE: servo question


> If we are really going to consider that a good coreless servo is going to
be
> blown-back enough to notice, what are the effects of control surface
flex??
> The area around the control horn is locked tight, but the farther away
from
> the control horn area, the less stable the deflection?
>
> -----Original Message-----
> From: discussion-request at nsrca.org
> [mailto:discussion-request at nsrca.org]On Behalf Of Troy Newman
> Sent: Sunday, August 03, 2003 2:26 PM
> To: discussion at nsrca.org
> 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
> > >
> > >
> > >
> > >
> >
> > =====================================
> > # To be removed from this list, send a message to
> > # discussion-request at nsrca.org
> > # and put leave discussion on the first line of the body.
> > #
> >
> >
> =====================================
> # To be removed from this list, send a message to
> # discussion-request at nsrca.org
> # and put leave discussion on the first line of the body.
> #
>
> =====================================
> # To be removed from this list, send a message to
> # discussion-request at nsrca.org
> # and put leave discussion on the first line of the body.
> #
>
>
=====================================
# To be removed from this list, send a message to 
# discussion-request at nsrca.org
# and put leave discussion on the first line of the body.
#