February 23, 2020

Pitch Servo Connector Issue

As I was laying out the wiring to the pitch servo, I realized there is a slight issue. Can you spot the problem in the next picture?

Pitch servo backshell

As you can see in that picture, there’s not much room between the autopilot connector and the neighboring rib, meaning the wires coming out of the plug backshell would crash into the rib. No good! Especially once I populate all the wires into the backshell, the wires will want to come straight out of the backshell 2-3 inches, much like my already-completed connector for the roll servo as seen in the next picture. I don’t want to risk the wires failing from being pressed up against the rib, subjecting them to rubbing under vibration.

Picture shows how the wires want to exit the backshell in their relaxed state

The backshell that Garmin supplies is custom, having a few airplane-specific features, like integral strain relief and threaded holes to screw down the shield drains. Garmin sells a 90-degree backshell, available via Aircraft Spruce, but it’s unreasonably expensive (almost 3X the price, $110 vs $30) compared to the straight backshell ! I decided to turn to my other usual electronics suppliers, since the plug type is a very standard 15-pin d-sub. Fortunately, I was able to find something made by NorComp, though it lacks screw holes for the shield drains. It will route the wires upward as desired, which should eliminate the fatigue problem. It also has a nifty strain relief. I will figure out a way to attach the shield drain – probably via the screws that clamps the two halves of the backshell together. A very reasonable solution, and this part cost only $6.

Here’s a link to the part I ordered: https://www.digikey.com/products/en?keywords=981-015-130r121.

90 degree shielded backshell – NorComp part 981-015-130R121

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