Interesting topic on Gizmag.

According to van Loenen, all the plastic parts, which include the clamps to attach the motors, can be 3D printed in ABS, with the appropriate files made available on van Loenen's website. The clamps used may not work with more unusually shaped objects, but there's nothing stopping anyone from designing their own custom variants.

http://www.gizmag.com/drone-it-yourself/28209/