[fasilpereira]

I'm installing a G3X system on a COMPOSITE airframe, with GSA 28 servos and Ray Allen trim servos with autotrim function as per G3X/G3x Touch Installation Manual. I'm using Figure 24-1.8 GMC 507/GSA 28 Interconnect Drawing as a reference for this installation.

The trim motor wires are connected to TRIM OUT 1/2 on the GSA 28. Figure 27-1.8 shows the trim motor wiring as a twisted shielded pair, with shield terminated to Garmin shield block ground on the GSA 28 connector and to the airframe ground on the trim motor end.

The problem is that I don't have any airframe ground near the servos. Will I have to take an additional ground wire up to the rudder, aileron and elevator for that?

Another weird thing to me is that the TRIM 1/2 wires are shown as unshielded wires. These are the wires that comes from the trim switches and are basically the same signal as TRIM OUT 1/2, but before the GSA 28.

Have you, RV builders, used a shielded pair for TRIM OUT 1/2? Have you grounded it to the aircraft structure or to a dedicated ground inside the control surfaces?

Thank you,

Fabricio

 

[g3xpert]

GSA 28 Trim Wiring

I'm installing a G3X system on a COMPOSITE airframe, with GSA 28 servos and Ray Allen trim servos with autotrim function as per G3X/G3x Touch Installation Manual. I'm using Figure 23-1.8 GMC 507/GSA 28 Interconnect Drawing as a reference for this installation.

The trim motor wires are connected to TRIM OUT 1/2 on the GSA 28. Figure 23-1.8 shows the trim motor wiring as a twisted shielded pair, with shield terminated to Garmin shield block ground on the GSA 28 connector and to the airframe ground on the trim motor end.

The problem is that I don't have any airframe ground near the servos. Will I have to take an additional ground wire up to the rudder, aileron and elevator for that?

Another weird thing to me is that the TRIM 1/2 wires are shown as unshielded wires. These are the wires that comes from the trim switches and are basically the same signal as TRIM OUT 1/2, but before the GSA 28.

Have you, RV builders, used a shielded pair for TRIM OUT 1/2? Have you grounded it to the aircraft structure or to a dedicated ground inside the control surfaces?

Thank you,

Fabricio

You will need to run a dedicated ground wire if that is what is required to meet the interconnect guidance. It is important to handle the shield grounding exactly as shown in the Installation manual for this connection. The signal generated by the GSA 28 that is sent to the trim motor is PWM, which is what makes it noisier than the switch wiring.

Thanks,

Justin

 

[Graham D]

Send a ground wire to a ground wire?
I would suggest blindly terminate the shield at the trim servo end as the trim servo is plastic anyhow.

 

[Walt]

I helped a friend install G3X AP in a Glasair III, in the end, after trying many different ideas, we were never able to eliminate the trim noise in the com radio. The com antenna is mounted in the VS, eventually we gave up.

 

[fasilpereira]

Walt,

My COM2 antenna is also at Vs….

What do you mean by “gave up”? Did you have make a direct wiring to the trim servo? That way you lost the auto-trim function…

Fabricio

 

[Walt]

Walt,

My COM2 antenna is also at Vs….

What do you mean by “gave up”? Did you have make a direct wiring to the trim servo? That way you lost the auto-trim function…

Fabricio

Yes, no auto trim, went back to stock electric trim setup.

 

[fasilpereira]

Ouch! Did the trim installation complies with all the G3X Iinstallation manual recommendations?

I hope I don't have the same issue. I have another aircraft with direct wiring to the trim and I'd really like to have the autotrim feature.

Thanks Walt!

Fabricio