Update V2: Strengthened some weak spots in the design and removed excessive fillets, simplifying the structure. Print with the hooks facing upwards. Only use supports in the upper triangular windows, otherwise it gets messy to remove them.
Battery compartment for the Quad. Best used in conjunction with these landing feet in order to get the space necessary underneath. I like my multis with a low CG. The comparment is made for 3S 1300 mAh LiPos and should fit most makes out there.
The little thingy between the upper an lower platforms on the rear view photograph is a BT module support that comes in many different configurations.