Avionics: AHRS Bracket.

Because I'm using GRT avionics, I am unable to use the AHRS tray provision in the stock wing kit, as the GRT box has a different shape and location requirements.

GRT requirements for AHRS installation:

1. Should be mounted in the cabin to prevent condensation.
2. D-sub connector should be pointed aft.
3. Length of box must be aligned with longitudinal axis of airframe and that box must be level in roll.
4. Pitch orientation isn't critical, though should match longitudinal axis of airframe.
5. Alignment between the magnetometer and AHRS should match with 0.5° in all directions. 
6. Should not be exposed to direct airflow from any source.
7. Must be mounted on a rigid structure.

These requirements exclude mounting in the wing.  So, my friend suggested I copy the approach he used in his RV-9A, which is to create a welded, rigid shelf mounted against the firewall on the aft side.

Doing some simple trigonometry, we found the correct angle and part lengths to create the below temporary proof-of-concept tray out of 0.125" thick stock.

I then created the parts in my CAD program for precision and had it cut and welded at a local waterjet joint.  It probably cost about $100.  Here's the CAD file I made.

Following priming the tray and the addition of flush-mounted nutplates, the AHRS unit was mounted on the tray and the assembly was then bolted on to the firewall with AN3 bolts.  The angles of the AHRS, the magnetometer (already mounted in the tail) and longitudinal axis of the plane (as referenced by the F-01418A longeron) all agree to the 0.1° precision of my digital level.

Should the unit need to be serviced, I'll have to get on my back and shove myself into the footwell, but it will be easy enough to release the d-sub connector, pitot, static and AOA lines and then unbolt the tray to lower and remove the box.

Don't mind the crazy wires.  I'm not done routing and affixing them.

Update 11-Sep-16:  I added some lightening holes, cut area away from the bottom to match AHRS base's footpring and removed some area from the upper corners.  I foolishly neglect to add (subtract?) those in my CAD design.  I wanted to put a hole on each triangular piece, but I didn't want to risk it.