[NSRCA-discussion] Random tip on ATV and setup

Sat Feb 21 10:38:05 AKST 2009

So Jim it's a good thing to set your ATV/AFR +100?

JLK

From: joddino at socal.rr.com
To: nsrca-discussion at lists.nsrca.org
Date: Sat, 21 Feb 2009 11:31:58 -0800
Subject: Re: [NSRCA-discussion] Random tip on ATV and setup

That is correct.  I'll talk about Futaba but the same applies to other brands though the numbers and terminology may be different.  The maximum resolution available is 2048 increments.  This means that a receiver channel output pulse width can be at any of 2048 values between 0.9 and 2.1 milliseconds.  This translates to... the servo output arm can be at any of 2048 angular positions.  In actual use we will have less resolution because to get to 0.9 or 2.1 you'd need to put the trim and subtrim hard over in opposite directions respectively.  But you do want to maximize the pulse width range and you do this by keeping the ATV and AFR high (over 100). I try to keep the pulse width in the 1.0 to 2.0 millisecond range.  I use a spline curve and don't use Dual rates.  Then one must use the mechanical linkage to get the proper throw.  

And yes if you reduce ATV or AFR you will reduce the range of pulse width values but it would not be correct to call that clipping or compressing.  I would call it lowering the dynamic range, but I better Google that to see what they say.

Jim

On Feb 21, 2009, at 9:40 AM, J N Hiller wrote:

Jim, I was under the impression that reducing travel using duel rates reduced the resolution unnecessarily. I never did really understand if the pulses were clipped or compressed with rate changes. Help!
Jim Hiller

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of James Oddino
Sent: Saturday, February 21, 2009 9:18 AM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Random tip on ATV and setup

Hi Don,

You lost me with this one and I must confess I didn't study the previous posts.  I did question your basic premise that using Subtrim was a bad thing.  I agree it is bad if it is being used to make up for a bad linkage setup but it is okay to use it as long as the servos are going through identical angles and the servo speeds are the same.  ( The servo speed, measured in degrees per second, is not a function of the transmitted signal.)

The way to approach twin elevator servos, is to match the servos prior to installing them in the airplane by installing the control horns as close as possible to their neutral positions with the stick, trims, and subtrims at zero and then touch up the neutrals with the subtrims.  You need a large protractor and pointer on the servo to do this. Then set the end points to the same maximum throws, to more than you would ever want.  Then touch up the neutral with the subtrim again and the endpoints again until they track exactly.  Then never touch the Subtrims and ATV again.  

Use the AFR or Dual rates to set your desired throws in the plane and do any neutral trimming with the normal trim.  These functions affect both channels equally if you are set up right.  Never use ATV or independent channel subtrims or end point adjustments to set the throw in the airplane.

Hope this helps.  I know it will force you to make perfect linkage setups if you want the elevators to track.

Regards, Jim O

On Feb 21, 2009, at 8:00 AM, tocdon at netscape.net wrote:

Bob,

Good article.  If the right elevator ATV is set up at lets say 120 percent (down elevator) then the other side is set at like 90 percent (up elevator)- what would the speed be to go down more than the speed to go up.   This is with respect to the left elevator, assuming its set at 100 percent up and down.  Since its less steps, and same step speed (1.17us per step) times 1024 equals 1.2 milliseconds times 60 degrees if throw is like .024 seconds, but with a servo speed of .2 seconds per 60 degrees times 2 (120 degrees throw total up and down) puts it at about 2 percent difference (of .4 seconds).  Maybe I should have gotten up early and gone with Chris to the WRAM...

Bottom line his program setup was straight out of the mad kitchen chef show.   When I asked him why he originally did not take the time to set it up mechanically, I just got kind of a blank stare-  like if the radio CAN do that, then what's the problem.   When we set everything to normal, zero sub trim, and mechanically adjusted the servos and control arms- everything worked fine.  Now this is an extreme example but I got to thinking that if you minimize these electronic setup things it will help with precision.   I try to use little or no subtrim, but do use ATV in the amounts up to 5  or 7 percent to get the end point throws just right. 

Cheers,
Don

-----Original Message-----
From: Bob Richards <bob at toprudder.com>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Sent: Thu, 19 Feb 2009 8:55 pm
Subject: Re: [NSRCA-discussion] Random tip on ATV and setup

Don,

If I am understanding this correctly, the servos are actually moving the same speed (degrees/second). However, because of the mechanical setup differences, the two servos were having to travel different amounts to get the two elevator halves to move the same amount. Regardless, you are correct that a problem in the linkage geometry should never be corrected using radio settings.

The step size of the 1024 Futaba radio is fixed, at 1.17us. I discovered this when I wrote about the Futaba radios in the Kfactor back in Jan '95.

http://www.toprudder.com/hobbies/fut7uap.pdf

Bob R.

--- On Thu, 2/19/09, tocdon at netscape.net <tocdon at netscape.net> wrote:

From: tocdon at netscape.net <tocdon at netscape.net>
Subject: [NSRCA-discussion] Random tip on ATV and setup
To: nsrca-discussion at lists.nsrca.org
Date: Thursday, February 19, 2009, 10:32 PM

Sub trim is a function that moves the servo to get the control surface centered. This in conjunction with end point adjustments can have an adverse effect on servo speeds. You are basically stretching the number of steps for the same amount of travel, among the servos. I was at the FARM club helping out a giant scale newbe last fall and he was flying a third scale H9 Extra 330 with Futaba 8 channel and Hitec servos. One of his servos literally trailed the other one by about 20 or so degrees when moving the elevators up and down in a rapid fashion. He said a servo was bad. Actually, backing up a bit- when he was flying he asked my help to trim his plane and handed me the transmitter . When I tried some waterfalls, it peeled off really bad. When I landed, that is when I saw the elevators moving at different speeds. Upon inspection I found he used the electronic sub trim to get the servos aligned and massive atv end point to get the ends the same throw. He also had the ATVs set at nealy 150 percent. I think he was like, off one complete servo arm tooth and used the sub trim to get the servo back to center. After about 2 hours getting everything mechanically adjusted, the plane flew so much better. It went from something nearly crashing to a competitive IMAC and 3D setup. Any case, I had an identical experience when helping a flyer in Vanceboro, NC last year (after the pattern contest completed). Exact same issue on his (scal e) plane. He thought the Rx was bad until I showed him what the deal was. After mechanically adjusting to get it close, all was well.

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