[NSRCA-discussion] Twin elevator servo issue using Futaba 9 ZAP

[Jay Marshall]

Can't you determine if it is a radio problem by switching the servos &
channels?
 
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Bob Richards
Sent: Friday, August 11, 2006 6:31 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Twin elevator servo issue using Futaba 9 ZAP
 
Brian,
 
I think there are two problems. 1) Movement commands from the radio arriving
at the servos at the same time (dynamic) and 2) Control surface throws
matching through the entire range (static).
 
What you are describing is a dynamic problem, ie: does the radio do all the
mixing and send the information to the servos *at the same time*.  In other
words, while the servos are moving, one is lagging behind the other since
the radio is processing one channel before the other. Also adding to the
dynamic problem are the speeds of the servos, they must be the same.
 
The other problem is what I was talking about, when the servos stop, are the
control surfaces tracking together. This depends on the linkage geometry as
well as the servos being linear.
 
A matchbox attempts to correct both problems. However, a matchbox only
matches 3 points in the entire travel range, and the problem described (as I
understood it) is that the throws don't match halfway between the neutral
and endpoints.  It would be nice if there were multiple points in the range
(5, or 7) that could be programmed in the matchbox. This feature could even
be used to program in expo, seperate from the transmitter.
 
Servos can have linearity problems due to the manufacturing tolerances of
the feedback potentiometers. I have seen pots (not from servos) that were
"adjusted" by milling away material around the perimeter of the conductive
material, but I wonder if anyone does this for the small servo pots used in
our systems.
 
IMHO, the processing speed is not as much of a problem for us, at least in
pattern, as we might think it is. It is much more important that the
surfaces end up at the same position, since that will affect the flight more
than the small difference in position *while the surfaces are moving*.
 
Bob R.


brian young <brian_w_young at yahoo.com> wrote:
I think this is a problem with the processing capability of the TX. You have
a progammed mix, it reads one channel then the next. I had a 9CAP where this
problem was very noticable. Now on my 9Z its not as noticable, it looks like
the slave servo is a little slow to catch up. Only real solution in my
opinion is a match box, y-cable or similar device.
 
I can sit back and pick which servo is the slaved just watching the
surfaces. 
 
Im understanding that your endpoints match when the surface are finished
moving, and the middle is matched as well. You should be able to stop at any
point in the travel and the pointers line up, when they stop moving. If this
is the case your linkage would be ok. 
 
I think the speed of the servos has passed the processing speed of the
radio.

Bob Richards <bob at toprudder.com> wrote:
That might be the cause, or it could simply be a difference in linearity
between the servos.
 
Bob R.


 
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