GMU11 Part 2

Time: 3 hrs

Things done today:

  • Removed old cabling for GMU22
  • Ran new #22-3 between GMU11 location and instrument panel
  • Ran CANbus cable between GMU11 and pitch servo
  • De-pinned CANbus pins from pitch servo connector
  • Pinned and installed 9 pin connector for GMU11

Today I did some prep work for the GMU11 even though I don’t have the new mount yet. The factory said they should be shipping them by the end of the week and sent me a drawing of where it will be mounted.

TAF photo of the new GMU11 mount and location in the rear fuselage. It should be doable from the access hole in the bottom.

I ran the power and CANbus wire for the GMU up the left center longeron. I probably would have picked a different route if I had more access to run the wire. I think this was the  best way for my situation since I can get to most of the longeron to drill and install cable ties. The cable splits here near the pitch servo. The #22-3 (power1&2 and ground) go to the instrument panel and the CANbus wire runs to the pitch servo connector to tie into the CANbus there. I ran a single bundle back from here to the GMU. I used a multicore wire wire for the power and ground rather then single wires just because the Garmin manual said to do this to cut down on any EMF.

Note (9-3-2017): Just realized that I should have used #20-3 wire since I’m tying this into a 5A breaker. Well the device isn’t going to pull nearly enough to heat up the wires (it only pulls 0.1A), but the wire would technically fry before the breaker pops. So I think I may move it to a smaller breaker (it was on a breaker shared by other Garmin stuff) and then it should be fine. Also it’s really hard to find #20-3 cabling so I probably would have had to use #18 which is really overkill.

The one problem with this route is the wire gets a bit close to the pitch servo. The tie in the upper right of the photo helps keep it away from the servo. I didn’t shrink the heat shrink here yet because I may have to adjust the split point a bit once I get the GMu installed. I wanted to leave enough cable on the GMU side so I could put the connector on.

Cables on the GMU side with pins and labels.

Connector almost done. I put silicon tape where the cable strain relief is to protect the wire and add some resistance. One important note is that the metal bar part of the restraining clamp has the raised part facing away from the wire. If you flip it over then it can eventually damage the wire.

All done, just need to get a stainless steel 8-32 screw and lock washer to attach the shield of the CANbus. I didn’t put a drain wire on the other multicore wire because you really should only connect the shield at one end of a shielded cable to minimize ground loop issues. The CANbus is one except to that rule. It would probably be OK to ground the shield for the other wire, but just keeping consistent. Also the terminator will be installed here as well since this will be the end of the CANbus. The GMU11 uses an external adapter for termination rather then a jumper.

NOTE: The ring terminal is a Raychem B-106-1401, I believe I ordered it from Mouser Electronics. It’s nice because it’s a crimp connector, but also is heatshinkable. This saves a step of crimping the connector and then adding heatshrink over the end of the connector.

Now just need to wait for the new mount and get that riveted in.


Miscellaneous Work

Time: 1 hr

Nothing exciting done today so no photos. I had been talking to another builder about the placement of the GMU. The manual puts it under the luggage area, but both the Garmin GMU22 and GMU11 specify a 10ft clearance from any motors. Well the pitch servo is only about 3ft away. I knew this but figured TAF had tested this… and they probably did with the GMU22. The Sling 4 at Torrance is all Garmin with an autopilot and the GMU is mounted under the luggage area and there’s no issue. The only difference is I’ll be using the newer GMU11 and not the GMU22. They both have the same distance requirements but it’s never been tested in that area. The builder I spoke with can and probably will move thiers further back in the rear fuselage. This isn’t so easy for me because my rear fuselage is already closed up. Mounting the GMU wouldn’t be too much of an issue, the problem is running the cable with limited access. So after looking and thinking a bit here’s my plan. I’ll remove the GMU mounting bracket so that I can more easily drill the new mounting holes. Then I’ll mount it back under the luggage area, but as far back as possible. I can get another 2ft or so clearance from the servo… anything will help. I also need to rewire a bit because the new GMU uses CAN bus. I’ll split off the pitch server for the CAN and make sure to use a terminator on the GMU since it will now be last in the change. And then I’ll just hope for the best. If there is a problem I can mount it in the wing or move it further back in the fuselage and deal with trying to run the cables at that time. 

I also installed the BNC ends for the Com1 and 2 antennas. I still need to purchase those. And lastly I messed around with some of the AN fittings on the parking brake lever and installed an AN fitting on the brake reservoir. 

Oh yeah I almost forgot to mention. I disassembled the throttle section so I could take the mounting plate to see if I can get it made up in Carbon Fiber. I’d also like to do the instrument panel and the guy said they can do all the instrument cut outs once I have that figured out.