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  #1  
Old 06-02-2021, 03:30 PM
mratzburg mratzburg is offline
 
Join Date: May 2017
Location: Madison, WI
Posts: 20
Default GMC507 Serial Connection to GSA28?

Myself and another builder were working together to add the GMC507 and GSA28 to my existing G5 system. While we were wiring the roll servo we wired in the serial pins on the roll servo. I only realized while pinning out the GMC507 connection that the GMC507 does not call for the serial connection as did the previous controllers. Is there any undocumented advantage of pinning it (as a backup for the CAN bus, for example) or is it simply unused with the GMC507?

Thank you,
Mark
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  #2  
Old 06-02-2021, 06:50 PM
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g3xpert g3xpert is offline
 
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Location: Olathe, KS
Posts: 3,050
Default GMC 507 Wiring

Quote:
Originally Posted by mratzburg View Post
Myself and another builder were working together to add the GMC507 and GSA28 to my existing G5 system. While we were wiring the roll servo we wired in the serial pins on the roll servo. I only realized while pinning out the GMC507 connection that the GMC507 does not call for the serial connection as did the previous controllers. Is there any undocumented advantage of pinning it (as a backup for the CAN bus, for example) or is it simply unused with the GMC507?

Thank you,
Mark
Mark,

The serial connection is unused in this case. With a GMC 305/307, the GMC controller communicates with the roll servo via serial, the roll servo then relays that information to the rest of the autopilot system via CAN. If you were to have an issue with the CAN bus, the servos would be unable to communicate with each other and the ADAHRS, and the Autopilot would be inoperable. The ability of the GMC 507 to communicate with the roll servo would be of no advantage in this type of failure.

Thanks,

Justin
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  #3  
Old 06-02-2021, 06:56 PM
gfb gfb is offline
 
Join Date: Jul 2014
Location: Madison, WI
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Default

Thx Justin.

Just looking for a little clarification. With the 305/307 is the serial a backup communication method? So the 507 just doesn’t have this backup?
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  #4  
Old 06-02-2021, 07:58 PM
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bjdecker bjdecker is offline
 
Join Date: Jun 2005
Location: Georgetown, TX
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Default

Quote:
Originally Posted by gfb View Post
Thx Justin.

Just looking for a little clarification. With the 305/307 is the serial a backup communication method? So the 507 just doesn’t have this backup?
The RS-232 channels are the *only* communication mechansim from the GMC 305/307 to/from the Roll Servo and the G3X Touch.

GMC 507 only supports CANbus.
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2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
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  #5  
Old 06-03-2021, 07:49 AM
mratzburg mratzburg is offline
 
Join Date: May 2017
Location: Madison, WI
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Default

Thanks Justin. That is what I thought but wanted to make sure.

Quote:
Originally Posted by g3xpert View Post
Mark,

The serial connection is unused in this case. With a GMC 305/307, the GMC controller communicates with the roll servo via serial, the roll servo then relays that information to the rest of the autopilot system via CAN. If you were to have an issue with the CAN bus, the servos would be unable to communicate with each other and the ADAHRS, and the Autopilot would be inoperable. The ability of the GMC 507 to communicate with the roll servo would be of no advantage in this type of failure.

Thanks,

Justin
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  #6  
Old 06-03-2021, 08:26 AM
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g3xpert g3xpert is offline
 
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Location: Olathe, KS
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Default GMC 3XX Mode Controllers

Quote:
Originally Posted by gfb View Post
Thx Justin.

Just looking for a little clarification. With the 305/307 is the serial a backup communication method? So the 507 just doesn’t have this backup?
As Brian mentioned, the GMC 3XX Mode Controllers do not communicate via CAN bus, the serial connection is the primary and only method of communication with the servos, displays and the rest of the LRU's. Page 27-9 of the AN revision of the Installation Manual provides guidance for using these units.

Thanks,

Justin
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  #7  
Old 06-03-2021, 10:40 AM
gfb gfb is offline
 
Join Date: Jul 2014
Location: Madison, WI
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Quote:
Originally Posted by g3xpert View Post
As Brian mentioned, the GMC 3XX Mode Controllers do not communicate via CAN bus, the serial connection is the primary and only method of communication with the servos, displays and the rest of the LRU's. Page 27-9 of the AN revision of the Installation Manual provides guidance for using these units.
Q: two scenarios:

1 - CAN dead: The serial connection still allows the GMC30X to drive the roll servo and keep wings level?

2 - Serial dead: you still have full autopilot control by using the G3X touch screen autopilot controls?

Thanks!
-Guil
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  #8  
Old 06-03-2021, 12:40 PM
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g3xpert g3xpert is offline
 
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Default Failure Scenarios

Quote:
Originally Posted by gfb View Post
Q: two scenarios:

1 - CAN dead: The serial connection still allows the GMC30X to drive the roll servo and keep wings level?

2 - Serial dead: you still have full autopilot control by using the G3X touch screen autopilot controls?

Thanks!
-Guil
1. No, if there is an issue with the CAN bus, the servos are unable to communicate with each other and the ADAHRS LRU. In this case the autopilot is inop, but your ADAHRS and EIS should have serial backups connected to the GDU so you would still have critical flight information available on your display.

2. Yes

Edit: One more interesting scenario to throw in there, if you have just one GDU and were to lose it in flight (or 2 or more GDU's and lose all of them), as long as the CAN bus is functioning properly, and the GSU 25/73, GSA 28 servos, and GMC Mode controller can communicate, you have basic wing leveler and altitude controls.

Thanks,

Justin
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Last edited by g3xpert : 06-03-2021 at 12:45 PM. Reason: Additional Note
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  #9  
Old 06-03-2021, 12:51 PM
gfb gfb is offline
 
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Thanks. Is this where the hidden ADAHARS inside the GMC507 comes in to play?
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  #10  
Old 06-03-2021, 09:27 PM
jliltd jliltd is offline
 
Join Date: Sep 2013
Location: Rancho San Lorenzo
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Quote:
Originally Posted by gfb View Post
Thanks. Is this where the hidden ADAHARS inside the GMC507 comes in to play?
I have never heard the GMC 507 has an internal ADAHARS. It doesn't have pitot and static lines so I don't know where the air data would come from. I guess maybe it does because I know the GFC 600 does. Or perhaps if the GMC 507 had anything it would be a backup attitude like a GDL 50 or GTX 345, but not a full ADAHARS like a G5. Also G3X Expert's post said you need the GSU 25 for the display failure wing leveler to work so I am assuming that the GSU 25 ADAHARS is the one it works with. I wonder if a G5 was on the CAN Bus network it too could stand in for a failed GSU 25 in the same scenario.
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