Lens protector and 30 degree tilt mount for the Xiaomi YI camera. The lens protector is designed to fit snugly over the lens of the camera with a friction fit. When the camera is inserted into the base, you can then attach the entire assembly by looping a velcro strap around the camera and through the frame of your quad. The mount is designed for a 15mm velcro (battery) strap. The channel for the strap is designed to make the power button accessible while it's still fastened to the frame.
There are two versions of the lens protector assembly - with and without the side mounting slots. If desired you can use the side slots to wrap an additional velcro strap around the camera horizontally to secure the assembly to the camera. In practice this isn't really needed as the strap securing the entire mount and camera to the quad also holds the lens protector firmly on the camera.
To protect the lens, cut a 31mm X 31mm piece of clear lexan (up to 2.5mm thick) and attach to the assembly. The mounting holes are in a 25mm square and accept M3 hardware.
Recommend you print the lens protector in black otherwise you may get some color reflection back into the lens from the lexan shield. Optionally use a black sharpie to color the ring around the lens as shown in the photos.
Here's a video log by a friend showing the mount and how to assemble it.
March 10, 2016 - Update
Added a vertical style lens protector and related base. The vertical style is meant to have a strap go throughout the top/bottom tabs and wrap around the base and quad frame. The protective lens dimension is 34x34mm. The related base has a cutout to fit the vertical lens protector. The vertical version has been printed and fits properly, but it's never been flight or crash tested. Since the strap doesn't go completely around the camera and is instead connected to the tabs, this style is potentially less robust. The failure point will likely be the tabs.
Recommend at least 3 shells for strength. You can adjust infill to balance strength vs. weight, but I recommend at least 50% - particularly for the base. You might be able to use a lower infill for the lens protector piece.
I have only printed and tested this with PLA. The parts are meant to be a tight fit so you may have to make some adjustments if you print with ABS to account for shrinkage.