BlueDog V4: Unibody Quadcopter

This is the version 4 of http://www.thingiverse.com/thing:973089.

Some of the changes from previous version, after test flying:

* Increased inter-arm distance on each side to 120 MM from the center of motor shaft.

* Main plate is 50 MM shorter at 150 MM

* Arms are thinner now, for a better air flow

* Arms and Main Plate can be printed separately and glued together.