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  #1  
Old 09-01-2016, 09:36 PM
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Greenley Greenley is offline
 
Join Date: Jan 2007
Location: Dowagiac, MI
Posts: 276
Default Connecting Garmin GAD 27, GSA 28, and trim

Looking for info on how to power the GSA 28 AP servos and trim when you have the GAD 27. The GAD 27 shows connecting the trim through it, but what about the GSA 28 servos, they also show connecting the trim to them. The GAD 27 install information makes no mention of the GSA 28 AP servos. I have seen a diagram someone posted showing the AP servos being powered from the GAD 27, and the trim from the AP servos, but no idea if this is right.
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  #2  
Old 09-02-2016, 08:13 AM
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g3xpert g3xpert is offline
 
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Location: Olathe, KS
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Quote:
Originally Posted by Greenley View Post
Looking for info on how to power the GSA 28 AP servos and trim when you have the GAD 27. The GAD 27 shows connecting the trim through it, but what about the GSA 28 servos, they also show connecting the trim to them. The GAD 27 install information makes no mention of the GSA 28 AP servos. I have seen a diagram someone posted showing the AP servos being powered from the GAD 27, and the trim from the AP servos, but no idea if this is right.
Hello Bill,

Since you have GSA28 autopilot servos and will likely want to use auto-trim, please connect the trim motors to the servos like shown on page 24-10 of the Rev. Z G3X Installation Manual.

This page also shows how to connect the trim switch inputs/outputs on the GAD27 to the pilot/copilot switches and to the servos.

Let us know if you have questions.

Thanks,
Steve
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  #3  
Old 10-11-2017, 02:58 AM
tgmillso tgmillso is offline
 
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Location: Launceston, Tasmania, Australia
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Hi All,
Does anyone know the reasoning behind why the power wires from the autopilot servo to the trim servo are shielded? The 5 core 26AWG wires supplied with the Ray Allen trim servos are not shielded, and nor are the power wires to the autopilot servo, so I'm a little confused as to why just this section of wire is.
Cheers,
Tom.

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  #4  
Old 10-11-2017, 05:26 AM
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g3xpert g3xpert is offline
 
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[quote=tgmillso;1210180]Hi All,
Does anyone know the reasoning behind why the power wires from the autopilot servo to the trim servo are shielded? The 5 core 26AWG wires supplied with the Ray Allen trim servos are not shielded, and nor are the power wires to the autopilot servo, so I'm a little confused as to why just this section of wire is.
Cheers,
Tom.

Hello Tom,

As you probably know, the GSA 28 servo doesn't simply turn the trim motor on/off to operate it in different directions using +12Vdc and ground.

It performs speed scheduled trim control where the trim motor is run fast at low air speeds and slower at high air speeds.

The trim motor speed is controlled by varying the trim motor drive voltage, and this is done by varying a high speed pulse width modulated (PWM) signal.

If you don't shield the wires carrying this signal to the trim motor, it can cause interference with other systems in the aircraft. In extreme cases we have even seen it break the COM radio squelch.

Thanks,
Steve
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  #5  
Old 10-11-2017, 05:52 AM
tgmillso tgmillso is offline
 
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Excellent. Thankyou Steve. This makes perfect sense. I knew there must have been some logical reasoning for it, I just couldn't quite put my finger on it.

Regards,

Tom.
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  #6  
Old 10-12-2017, 08:27 AM
YvesCH YvesCH is offline
 
Join Date: Feb 2015
Location: Basel, Switzerland
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Ouff thank you very much Tom for asking this! I did not realize that there is a requirement for shielded wire and wanted to rivet my turtle deck very soon! It would have been a pain in the a... to do it afterwards!

cheers, yves
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  #7  
Old 10-15-2017, 05:58 AM
tgmillso tgmillso is offline
 
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Location: Launceston, Tasmania, Australia
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Hi Steve. Do you need to run this shielded cable all the way to the trim servo, or can you just terminate the ground at the aft deck for the roll servo and assume that this far back on the fuselage you should be out of the danger zone from an interference perspective, and just run unshielded from the elevator to the trim servo? The only other equipment I have down the back of the aircraft is a shielded LED tail light (the magnetometer is in the wingtip). The reason I ask is that setting up a grounding point in the elevator is going to be much more difficult than on the aft deck.
Cheers,
Tom.
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