[NSRCA-discussion] Random tip on ATV and setup
James Oddino
joddino at socal.rr.com
Sat Feb 21 10:32:04 AKST 2009
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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