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

[J N Hiller]

Thanks James that was quite informative. I had no idea that the high-end
radios actually addressed the stick centering problem that well. Maybe they
are worth the extra cost, than again with thumbs similar to Ron’s and wings
out of level a good part of the time the benefit will likely be lost to many
of us especially when our turnaround returns aren’t a third of a mile ling
anymore.
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: Sunday, December 23, 2007 10:09 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Futaba and pattern ( A plus for Futaba)

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 <mailto: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>  [
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 <mailto: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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