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  #11  
Old 11-28-2018, 12:04 PM
Raiz Raiz is offline
 
Join Date: Nov 2009
Location: Cambridge, UK
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Thank you Steve and Mark, I hadn't appreciated how it works. One more question though, is it the 5 amp autopilot breaker (supplying the GSA 28) that limits the current to the trim motor while the GSA 28 is powering it or is there some other mechanism at work?

Ray
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  #12  
Old 11-28-2018, 01:47 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
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Quote:
Originally Posted by g3xpert View Post
One thing to remember is that the trim motor(s) are rarely powered by the GAD 27.

In normal operation the GSA 28 servos are always powered-up, and even when the autopilot is disengaged, the servos are providing speed scheduled variable voltage to the trim motors independent of the GAD 27. The GAD 27 is only providing trim direction signals to pins 11,12 of the GSA 28 the majority of the time.

It is only when the GSA 28 is powered off (a trim bypass relay drops) and non speed scheduled direct drive power is being supplied by the GAD 27 to the trim motor does the size of the GAD 27 trim power circuit breaker make any difference.

Thanks,
Steve
Hi Steve,
I have this setup as well and just began flying so I am at the very early stage of it. One thing that I have noticed when I operate the pitch trim servo all by itself (i.e. Auto pilot is powered off) the trim servo runs in a steady mode as long as I am pressing the switch on the stick but if the A/P is powered on and disengaged, the trim motor does not seem to run steady.

This observation is primary based on the sound that the trim motor makes. with the A/P turned off, I hear the trim motor (Ray Allen) noise continuously but with the A/P powered on it sounds as if it is pulsing rather a stead noise.

One other thing that I have noticed during the initial setup of the auto pilot, if I touch the trim switch on the stick it will disconnect/disengage the A/P, is that a normal operation?
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N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Phase one
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  #13  
Old 11-28-2018, 01:50 PM
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g3xpert g3xpert is offline
 
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Location: Olathe, KS
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Quote:
Originally Posted by Raiz View Post
Thank you Steve and Mark, I hadn't appreciated how it works. One more question though, is it the 5 amp autopilot breaker (supplying the GSA 28) that limits the current to the trim motor while the GSA 28 is powering it or is there some other mechanism at work?

Ray
Hello Ray,

Yes, since the GSA 28 servo is providing power to the trim motor, the circuit protection provided for the GSA 28 is sourcing the power.

Thanks,
Steve
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  #14  
Old 11-28-2018, 02:33 PM
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g3xpert g3xpert is offline
 
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Quote:
Originally Posted by Bavafa View Post
Hi Steve,
I have this setup as well and just began flying so I am at the very early stage of it. One thing that I have noticed when I operate the pitch trim servo all by itself (i.e. Auto pilot is powered off) the trim servo runs in a steady mode as long as I am pressing the switch on the stick but if the A/P is powered on and disengaged, the trim motor does not seem to run steady.

This observation is primary based on the sound that the trim motor makes. with the A/P turned off, I hear the trim motor (Ray Allen) noise continuously but with the A/P powered on it sounds as if it is pulsing rather a stead noise.

One other thing that I have noticed during the initial setup of the auto pilot, if I touch the trim switch on the stick it will disconnect/disengage the A/P, is that a normal operation?
Hello Mehrdad,

Congratulations on your new RV-14A. Really beautiful!

When you power off the servos and run the trim motor, it is running full speed at a steady max voltage and there is no speed scheduling which affects the trim motor speed/voltage.

When you run the manual trim with the servos powered, speed scheduling is being applied, which is done with a pulse width modulated (PWM) signal.

Depending on the speed scheduling setup, the trim motor will run slower in some conditions, and this could make it sound different.

There is a limit to how much the servo can reduce the voltage to the trim motor and still have it move, so at some point it even pulses the motor to further reduce speed, so this is something else you might have heard.

If the pilot pushes the trim buttons when the autopilot is engaged (with auto-trim enabled), it assumes the pilot is trying to take over control of the trim motors, and disengages the autopilot.

Let us know if you have additional questions.

Thanks,
Steve
__________________
Garmin G3X Support
g3xpert@garmin.com
1-866-854-8433 - 7 to 7 Central Time M to F
Please email us for support instead of using Private Messaging due to the limitations of the latter.
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  #15  
Old 11-28-2018, 02:49 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 2,506
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Quote:
Originally Posted by g3xpert View Post
Hello Mehrdad,

Congratulations on your new RV-14A. Really beautiful!

When you power off the servos and run the trim motor, it is running full speed at a steady max voltage and there is no speed scheduling which affects the trim motor speed/voltage.

When you run the manual trim with the servos powered, speed scheduling is being applied, which is done with a pulse width modulated (PWM) signal.

Depending on the speed scheduling setup, the trim motor will run slower in some conditions, and this could make it sound different.

There is a limit to how much the servo can reduce the voltage to the trim motor and still have it move, so at some point it even pulses the motor to further reduce speed, so this is something else you might have heard.

If the pilot pushes the trim buttons when the autopilot is engaged (with auto-trim enabled), it assumes the pilot is trying to take over control of the trim motors, and disengages the autopilot.

Let us know if you have additional questions.

Thanks,
Steve
Thank you Steve, I really appreciate the clarification. This all makes sense, the only puzzling part is that my speed schedule is set to 100% for 70knots but I was on the ground when I was testing this and speed was Zero. I would have thought that it would give me the full speed with the A/P on.

But I wasn't looking at the trim tab since I was in the cockpit so could not verify if the speed was slower, only could hear a pulsing sound.

Lots to learn with the new toys
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N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Phase one
Dues paid
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  #16  
Old 11-28-2018, 03:14 PM
Raiz Raiz is offline
 
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Thanks Steve
Ray
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