Notes to Self 3

[spbyrum]

If I'm following this correctly, putting the servo on its side so that
servo arm and control horn move in the same plane makes this simpler.
As the servo arm rotates and becomes shorter and less effective the
control horn becomes shorter and more effective.  If they were the same
length to begin with, the effects should cancel each other and we get
linear movement.  Right?
 
Steve Byrum 
-----Original Message-----
From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]
On Behalf Of Jon Lowe
Sent: Thursday, February 10, 2005 10:18 AM
To: discussion at nsrca.org
Subject: Re: Notes to Self 3
 
What he is saying is this:  As the servo arm rotates from 90 degrees,
the effective length of the servo arm gets shorter, meaning that for
each incremental degree of rotation of the servo arm from 90 degrees,
you get less incremental movement of the pushrod.  Therefore the control
is inherently more sensitive around neutral than it is at the ends of
the servo throw, assuming linearity in the rest of the system.  Expo can
be used to counter this natural tendency.
 
HOWEVER, the effective length of the surface control horn also gets
shorter as the surface moves from neutral, increasing movement with each
incremental movement of the pushrod.    So it is a race between
decreasing effectiveness of the servo output arm vs. increasing
effectiveness of the control horn.  Then you get into non-linearity of
the aerodynamic surface effectiveness itself as it moves from neutral,
and you can get confused real quick.  You are dealing with several areas
of non-linearity, and trying to compromise between them all.
 
Jon Lowe 
-----Original Message-----
From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]
On Behalf Of Tim Taylor
Sent: Thursday, February 10, 2005 8:28 AM
To: discussion at nsrca.org
Subject: Re: [SPAM] Re: Notes to Self 3
Troy let me get this straight in my mind, You said
 
"The reason is the servo wheel is round and its Y axis distance changes
for each degree of travel as the servo rotates around the back side."
 
Now It took me a few readings and some pondering to understand what you
said. It doesn't matter what type arm you use,correct so far? What I
take this to mean is as the servo arm moves the point at which the servo
is connected to the driving rod and the center arm screw is at it's
farthest point at 90 degrees to the servo case (assuming the servo case
is 90 degrees to the hinge line) as it moves forward or backwards the
distance between the pivot points decreases with each degree of
rotation. Correct?
----- Original Message ----- 
From: Troy A. Newman <mailto:troy_newman at msn.com>  
To: discussion at nsrca.org 
Sent: Friday, February 11, 2005 11:05 PM
Subject: [SPAM] Re: Notes to Self 3
 
8103, 9303 and 10X expo are the same Positive is softer and Negative is
harder feel. I'm writing an article for the KF right now that talks
about Expo and how to use it. When to use it. And the effects of it.
Sometimes a reverse expo (faster response) at center can be of benefit.
We have played with this in snaps and found that it has some
promise...Lots of regular expo on the ailerons and rudder and reverse
expo on the elevator...The result is the model will pitch harder on
entry before the rotations.
 
Another thing depending on the radio it takes 20-30% expo just to get
the output to be linear. The reason is the servo wheel is round and its
Y axis distance changes for each degree of travel as the servo rotates
around the back side.
 
This is March KF stuff so I won't elaborate here but I have some data to
back up my words. 
 
Troy
 
 
----- Original Message ----- 
From: T <mailto:tncbrown at charter.net> &C Brown 
To: discussion at nsrca.org 
Sent: Wednesday, February 09, 2005 8:42 PM
Subject: Re: Notes to Self 3
 
That is odd Tim.  I wonder why JR decided after all these years to
change from a pos. setting to a neg. for a "softer feel".  I'm a firm
believer in "If it ain't broke, don't fix it"  
I made the same mistake a few years back when I switched from a Futaba
7UAP to a JR 8103 and inadvertently put neg. expo in the 8103.  Talk
about pucker factor for a few minutes. 
Maybe Fu-tuh-boo-boo is rubbing off on JR!  (BG)
 
T-Bone
 
----- Original Message ----- 
From: Tim Taylor <mailto:twtaylor at ftc-i.net>  
To: discussion at nsrca.org 
Sent: Wednesday, February 09, 2005 12:18 PM
Subject: Re: Notes to Self 3
 
That's the whole point in the story Ron, I ASSUMED I was right and
didn't NEED to RTFB and could have screwed up big time. I've been flying
JR radios for years but always a PCM10 of some sort, this 9303 is a new
radio for me. What I did was get in a hurry, I wanted to fly and trim
this airplane and didn't do what I should have done first. I hope my not
so comical errors will help someone else from making the same mistake I
did.
----- Original Message ----- 
From: Ron Van Putte <mailto:vanputte at cox.net>  
To: discussion at nsrca.org 
Sent: Wednesday, February 09, 2005 12:01 PM
Subject: Re: Notes to Self 3
 

On Feb 9, 2005, at 8:28 AM, Tim Taylor wrote:
As our Continuing story unfolds........
 
Timmy T is looking out of the shop door and sees that the weather is
just perfect for some trim flights
 
So we pack up the trailer and go for some trim flights. Recalling the
last flights  all control throws too sensitive so I dial in less rates
on low and put high rates to what low was before. Ok time to dial in
some Expo on all surfaces, pop up the screen on the 9303 and dial in
30%. Ok time to fly. Airplane seems pretty stable now but the controls
feel a bit "Twitchy" hmmm no problem continue the flight land and have a
look. Ok maybe I didn't get enough expo dialed in so add some more. Next
flight about the same but the controls seem a bit more "twicthy" hmmm
something's not right here. Ok times up for flying for today pack up and
head home. On the way home I get to thinking about the last flight and
how the airplane changed the "feel" after I added the expo. Ok I get to
wondering where the heck did I put the book for this new radio, Ok lets
review the book on page A20 is the expo directions, it states "NOTE: Use
only positive percentages unless there is a distinct need to do
otherwise". Hmmmmmm that don't sound right! Turn the transmitter on and
look at the expo I've got dialed into the radio,
*&%^$*&#)(#&%^%)@(_*&_(^#  Everything is done to the NEGATIVE !!!!!! No
damn wonder! So "Note to self" today's lesson is READ THE FRIGGIN BOOK
!!!!!!!!!
 
Ok while I'm at it lets program a little down elevator  trim at low
idle, I wonder what page that is on in the book.................. "Fade
to Black as Timmy T reaches for the book."

My guess is that he's using a JR radio, because negative exponential is
what you want on a Futaba transmitter to soften the control response.
That's why well-meaning people at the field need to find out what brand
of transmitter the guy being counseled has before telling him how to
change the expo. 

I had a similar situation when I was helping a novice trim out his
airplane. After I flew a trim flight for him, I told him he needed 50 -
60% exponential on elevator and aileron. I asked him if he knew how to
do that and he said that he did. The airplane was a handful on the
subsequent flight, because he put in the wrong expo!

Ron Van Putte
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