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

[brian young]

I agree, I reread his post after sending my initial response and posted my error. 
   
  I do feel like when I replaced a program mix w/ a matchbox my vertical tracking was better. This was on the 9Cap and its worse than the 9Z. 
   
  As you pull through a radius if one surface is slower it should induce a small amount of roll untill the surface catches up. How much difference does it make? I dont know, but its something I can make not happen with a match box. I guess just depends on how picky you want to be, usually im not that picky as pattern guys go but had this vertical tracking problem once driving me nuts and noticed that slaved surface going slower so tried a matchbox. (Plus double checked and made my links as good as I could.)
   
  Anyway thats just my take.

Bob Richards <bob at toprudder.com> wrote:
    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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