Avada 2 - Improved duct guards

I remixed DaveDux3D's work. His design was a bulkier TPU effort, where he wanted the TPU to act as a bumper of sorts. However, I don't feel that approach is very effective, as the TPU transfers too much kinetic energy directly into the Avata's frame. The new approach I've taken, I've eliminated more than half of the material (make them MUCH lighter), and I'm actually printing them in PLA. The main reason for this, is that the guards are simply meant as a mounting mechanism to allow you to zip-tie on Polyurethane Foam (like what you find in high end packing materials) to the drone. The benefits of this are many:

1) Polyurethane Foam is MUCH better at absorbing kinetic energy than TPU.

2) You can have as much or as little Polyurethane Foam as you want! Allowing you to dial in the amount of impact resistance you'd like to have, verses flight characteristics.

3) You can easily shape the Polyurethane Foam to allow you to have more protection above and below the drone, giving