[NSRCA-discussion] Futaba and pattern ( A plus for Futaba)

[James Oddino]

Bob,

I would think that 256 resolution would mask poor stick centering.   
Think about 3 step resolution. Right, neutral left.  When you select  
neutral it is always the same unless you move the stick to the extreme  
where you get right or left.  The problem is you can't trim neutral  
unless you do it with another channel like folks did back in the reed  
days.  Move the servo with another servo.

You had many factors affecting trim in your 8 bit system starting with  
drift in the servos and an AM link that introduced large changes in  
pulse width to the servos as signal strength changed.  You could  
adjust linkages everyday and not keep up with everything that was  
fighting you.

So if low resolution masks poor stick centering then more resolution  
must emphasize it.  This has always bothered me.  I learned long ago  
that the servos can resolve pulse widths that would appear to be in  
the servo deadband.  In the early dual rate schemes we had to adjust  
the neutral if we changed the dual rate setting.  I tried using a  
servo to do this.  Adjust the pot until the servo didn't move as I  
switched the dual rate switch back and forth. Go fly.  Every time I  
threw the rate switch the trim would change.  Went home looked at it  
on a scope and sure enough the pulse width was changing.  Adjusted it  
so it didn't and the trim didn't change with the position of the rate  
switch when I flew.

This week I got a Futaba 14MZ.  I checked the stick centering with a  
scope.  Not perfect.  Plus or minus a few bits.  Now a bit in a 2048  
is only about a half of a microsecond change in pulse width to the  
servo so most folks don't care.  However I found that with the line or  
spline curve programming of the control sicks I can put in a plus and  
minus .5% deadband in the stick.  Now the centering is perfect no  
matter how I return the stick to neutral and I can trim it in .5  
microsecond increments.

I love this high tech stuff.

Jim O


On Dec 23, 2007, at 5:37 AM, Bob Richards wrote:

> Jim,
>
> You may be correct, the stick centering depends on the quality of  
> the stick. But, throw in 256 instead of 1024 resolution, the step  
> size is now 4 times as much and it would be much more noticeable.
>
> Ok, if we were flying the 4 channel Conquest transmitter (cheap  
> plastic gimbals) with 148 servos (non-ball bearing) in a slow moving  
> trainer, we probably could not tell the difference between 256 and  
> 2048 resolution. So, would I be better to fly a Conquest radio in  
> pattern? That seems to be the type logic I would get from people  
> that say 256 is "better than most servos".
>
> Oops, I forgot the Conquest is an analog radio. No steps  
> whatsoever. ;-)
>
> Bob R.
>
>
> J N Hiller <jnhiller at earthlink.net> wrote:
> Guys I don’t believe the mechanical stick centering is absolute  
> enough especially on a somewhat used radio at least on less than top  
> of the line transmitters. The detent design and pivot bearings are  
> less than shall we say industrial quality. Bob, I had the roll- 
> centering problem you described with my super 7 and felt it was due  
> to stick centering not being equal from either left or right. I  
> think my 9-C is better but not absolute. I wish I had one of those  
> little devices that displayed the signal count to verify my suspicion.
> Jim Hiller
>
> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org 
> ]On Behalf Of Bob Richards
> Sent: Saturday, December 22, 2007 3:37 PM
> To: NSRCA Mailing List
> Subject: Re: [NSRCA-discussion] Futaba and pattern
>
> Ron,
>
> All I can say is, I flew the Micropro with every intention of  
> competing at the '93 NATS with it. I had trimming issues with my  
> plane that I could not tune out. Some flights would be good, some I  
> could not trim the plane for level flight (slight roll left or  
> right). And, yes, I had taken out all the throw I could mechanically  
> so I had 100% throws programmed into the radio. Frustrated, I  
> decided to put my 7UAP in the plane, and it immediately felt good.  
> That is when I decided to do a little digging and discovered the  
> resolution issue.
>
> Whenever I mention that 256 is not good enough, I hear all sorts of  
> reasons why 256 should be sufficient. Yes, once the stick is moved  
> away from center, 256 probably is good enough. But when the stick is  
> at center, the darn servo better go back to the same position every  
> time. And you need fine resolution at center so the neutral position  
> can be varied in small enough amouts to arrive at precisely the  
> desired position.
>
> With a slightly worn stick or pot, the neutral position might be  
> bouncing between two adjacent steps. With 256 resolution, this can  
> be VERY noticeable. With 1024 or higher resolution, not nearly as  
> noticeable, if at all.
>
> Given the outcome of the '93 season with my old 7UAP, I'm glad I  
> switched out the radios.
>
> Bob R.
>
>
> Ron Van Putte <vanputte at cox.net> wrote:
> Hmmmm, I never thought of blaming my radio's resolution for my bad  
> flying.  Let's see now..........
>
> Ron Van Putte
>
>
>
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