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  #1  
Old 10-01-2017, 06:22 PM
JDA_BTR JDA_BTR is online now
 
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Default Roll trim, G3X and the 50-50-90 rule....

Any good nuke submariner knows that if you take a 50/50 shot you will get it wrong 90 percent of the time; and so it is with roll trim. I'm trying to improve my odds:

I'm installing the roll trim kit in my 14, with the wings still on the stand. No roll servo in yet, but soon/later. The plans say to just wire up the servo; no problem if it is backwards later we can just switch wires. But it isn't just a simple switch system. In the G3x system a stick switch drives the GAD27, and that drives a trim line (by relay in the GAD27), on to the roll servo, and then to the trim motor.

So one feature of this is that the roll servo will trim the ailerons to reduce torque on the roll servo, automatically. Thus make it live longer, use less power, all that good stuff. But how does it know which way to go? How would I know if the line is backward later between the roll servo and the trim motor? Does it even work if the wiring is backwards?

For that matter, how do you know what is up and what is down at the GAD27 to connect to the roll servo correctly.

Looking at the G3X Install manual (Rev AB here) on page 25-3, we find that the GAD27 J272 pins 9 and 10 have that function out to the roll servo "left or right". Is pin 9 "left"? Lets say we connect it to pin 11/12 on the roll servo J281, and it outputs to J281 pins 13/14. Then output pin 13 should be left? And I would make sure that wires to the trim motor in such a way that hot out of 13 turns the plane left?

Taking that one more step, at the trim motor connector, pins 4 and 5 are the pins for the motor drive. Pin 5 on the trim motor connector maps to pin 13 on the servo output using the supplied wing harness. So in the end it seems I should set up the wires on the trim motor so hot 5 and ground 4 moves the trim to turn the plane left.

Plane turns left when right aileron is down. This is when the aileron push tube moves toward the tip and away from the fuse. So it would seem that I need to figure out which wire is hot when the lever on the trim motor moves to the tip, and get that into the connector on position 5 of the trim motor connector...... so it is on pin 13 of the roll servo trim output.....

But all that assumes that on the GAD27 J272, pin 9 at 12V and pin 10 at gnd is intended to turn the plane more left. Is that true? Did I mess anything else up in this analysis?
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  #2  
Old 10-01-2017, 06:52 PM
rvbuilder2002 rvbuilder2002 is offline
 
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If I remember correctly (it's been 6 months already since I worked on a G3X install), since the G3X is all software controlled you get to teach the system which way is trim left and right so it doesn't matter if the wires are reversed.
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  #3  
Old 10-01-2017, 06:59 PM
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g3xpert g3xpert is offline
 
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Hello JDA,

It is pretty easy to follow the wiring guidance from the GAD 27 to pins 11,12 on each servo, but knowing which way to connect the two trim motor wires to pins 13,14 on the servo are probably best verified by testing.

Here is a simplified version of the steps explained in the G3X Installation Manual to configure/test your trim installation.
  1. Power off the servos.
  2. Use aircraft trim switches to run the trim motor. If the trim motor runs in the wrong direction, swap the trim motor wires at the control stick, at the servo on pins 11,12 (switch inputs), at the servo on pins 13,14 (trim motor drive wires), or at the trim motor itself.
  3. Verify that the trim now runs in the correct direction with the servos powered off.
  4. Apply power to the servos.
  5. Use the on screen controls on the servo configuration page to drive the trim motor for that servo.
  6. If trim motor runs in the wrong direction, change the trim motor direction setting on that page from Normal to Reverse (or Reverse to Normal if it is presently Reversed).
  7. Re-verify that the trim operates correctly in both the servo powered on and servo powered off conditions.

Let us know if you have questions.

Thanks,
Steve
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  #4  
Old 10-01-2017, 07:09 PM
Mark H Mark H is offline
 
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The trim direct is configurable on the G3X as Scott said. Just make sure if you have two switches for the trim that they are wired the same. You cannot switch the direction on just one switch, so if one moves it right and the other left, then when you will need to rewire one of the switches.
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Old 10-01-2017, 07:36 PM
n982sx n982sx is offline
 
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I had to switch mine via software in the G3x touch system. Easy, no rewiring.

Pitch trim is configurable the same way, but mine was fine.
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  #6  
Old 10-01-2017, 08:14 PM
JDA_BTR JDA_BTR is online now
 
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Thanks good info! 50/50 doesn’t seem so bad now!

Just for my own curiosity which pin goes hot on the servo connector for a normal left turn?
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Last edited by JDA_BTR : 10-01-2017 at 08:18 PM.
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  #7  
Old 10-01-2017, 11:56 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by JDA_BTR View Post
Thanks good info! 50/50 doesn’t seem so bad now!

Just for my own curiosity which pin goes hot on the servo connector for a normal left turn?
The two wires on the servo for driving the motor are both white, so there is no way to know without testing it.
A common 9 volt battery can be used for function testing if you want to check.
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  #8  
Old 10-02-2017, 07:08 AM
JDA_BTR JDA_BTR is online now
 
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Yes, I had to do that to drive the arm to center, and to see which wire moved the servo. I think that all of the input/outputs on the daisy chain are likely 1/1 and never swap down the line so if I use the convention left turn is the first pin I'll get it right first time..... But it would be nice to know which way the servo picks it. But since it is in software too it doesn't really matter at that point.
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