servo question

[george kennie]

<<<<am I all wet on this?>>>>

No toweling required on this one.Sounds like a very dry guy to me!

Troy Newman wrote:

> So you are saying Pre-load ailerons down so when they blow back...they go to
> neutral?
>
> I'm not saying that.....I'm saying that if the ailerons are held as stiff
> and with as little blowback as possible....it will help the loops
>
> The amount of blowback the aileron gets in a push or pull will likely vary a
> little depending on the servo, linkage, and servo mounting...By limiting the
> amount they blow back with eliminate the amount of error seen and will help
> the corners...The issue is not so much that they are moving....its that they
> are moving un-equal amounts....The more they are allowed to move the more
> error there can be.
>
> The digital servo with its huge holding power will limit the movement thus
> the error is limited as well.
>
> am I all wet on this?
>
> TN
> ----- Original Message -----
> From: "JOddino" <JOddino at socal.rr.com>
> To: <discussion at nsrca.org>
> Sent: Sunday, August 03, 2003 6:00 PM
> Subject: Re: servo question
>
> > 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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