Notes to Self 3

[Ron Van Putte]

On Feb 10, 2005, at 10:31 AM, spbyrum wrote:

> 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?

Yep.

Ron Van Putte

>  -----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
>
> 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&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
>
> 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
>
> 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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