Another tricopter inspired by the RCExplorer design.
The design does not require the hacking of any components; and keeps the none printed parts as few and inexpensive as possible.

Update: YCOPTER is compatible with RotorBits parts from HobbyKing. I used 2X RotorBits motor mounts (SKU:171000355-0), 1X RotoBits Servo Mount Set w/gear (SKU:171000393-0), and 3X carbon fiber square tube 10X10X250mm (SKU:078000007-0)
See new photos with the RotorBits parts.

KK2 flight controller case: http://www.thingiverse.com/thing:124122
APM 2.5 flight controller case: http://www.thingiverse.com/thing:129411

Print and assemble using lots of zip-ties. See photo for zip-tie locations.
The YCOPTER is designed for the standard RCExplore tricopter motors (DT750) and servo (BMS-385DMAX), other components may or may not fit.
Additional parts and instructions:

• 10mmX10mm bass wood or carbon fiber booms. 2X 275mm for the front arms, and 245mm for the tail.
• 2X 3mm, 25mm bolt + 4X washers + 2X lock-nuts for the arm pivots. The pivot hole for each arm is located 5mm for the end, on center. (6-32 X 1" bolt/washer/nut set will also work with some drilling)
• One 5mm X 50mm long bolt + 2X washers for the tail motor mount. (10-24 X 1" bolt/washer will also work) The tail boom needs to be drilled and tapped for the bolt thread. The printed tail motor mount through hole needs to be reamed out for a perfect fit. Lubricate the hole with Teflon or graphite powder.
• Some 50lb Spectra fishing line or equivalent as the servo control cables. String the line as shown in the photo. Each side is a separate cable. Wrap some rubber band between the two cables to take up the slight slack.
• 2X #4, 3/8" wood screws for mounting the servo.
• 4X 3/4"id O-rings. Two O-rings on each arm keep it in place during flight. Slip them off to fold the arms during transport.
• After the YCOPTER is assembled and aligned, improve rigidity by adding a bit of epoxy adhesive to the joins between the booms and printed parts; motor mounts, servo mount, legs and tail boom to body. Also put some on the cable knots to prevent them from untying.