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Servo Resolution

Old 11-07-2010, 02:50 PM
  #1  
JohnMac
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Default Servo Resolution

I am looking for some advice regarding the 7950 TH servos. I have installed these servos throughout my F14, but the pair I am concerned about drive the tailplanes. On this model the all flying tailerons utilise a hard closed loop system, with 4 high quality ball links on each, and 3mm hardened steel link rods. However this means that the angular movement of the servo arm is directly translated to the taileron, and it is much too much movement.
In an ideal world the servo movement should be split roughly equally between aileron and elevator travel, totaling around 100% travel, in order to maximise the mechanical advantage and utilise the enourmous power of this servo to its best. In reality I have had to reduce aileron and elevator tral on the transmitter to around 20% of movement for each, so only around 40% of the servos travel is utilised. Hardly ideal, and the result is very jerky taileron movement and poor centreing.
So to my question. If I reduce the servo travel in the servo itself using either the Hitec programmer or Multiplex Multimate, will I get better resolution at the end or will it make no difference to the end result?
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Old 11-08-2010, 11:08 AM
  #2  
Brendan Lugo
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Default RE: Servo Resolution

You should still have the same full resolution with the new shorter travel range.
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Old 11-08-2010, 01:35 PM
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JohnMac
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Default RE: Servo Resolution

Hi Brendan,
Thanks for the reply. So I would be better to reduce the servo travel with the programmer, and use full travel on the Tx, right?
Thanks,

John
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Old 11-11-2010, 09:13 AM
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mglavin
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Default RE: Servo Resolution

John,

Why not provide linkage ratios that allows more servo angle first?
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Old 11-11-2010, 03:38 PM
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JohnMac
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Default RE: Servo Resolution

Hi Michael,
Because the system is not designed in such a way as to allow this. The all flying tailplane pivot rod is clamped into a a tube within two bearings, supported by a metal cage. This cage also suppots the servo. Each side of the clamp tube is a horn fitted with ball links on 3mm steel rods. These lead to the servo output arm which is double sided and the centres are exactly the same as the clamp tube horns. The system is designed to minimise any possibilty of slop, which it does extremely well, but at the expense of any gearing from servo to control surface.
The next problem is that this model is so large that it needs exemption certification from the CAA (same as your FAA) and to alter a proven design is a default fail. I would have to redesign the system and PROVE that it would not fail. Huge can of worms that I have no intention of opening so I have to find another solution. If reprogramming the servo down to circa 50% travel results in the standard resolution being available over the remaining travel, I will be quite happy.
As it is now, with the travel reduced at the Tx, the tailplane movement is very jerky.
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