Printing moving parts as one whole???

[JustAddMilk]

the best ones are just brilliantly designed.
Check out the lefab shops stuff on thingiverse.
The robot has 13 moveable joints and prints without supports.
amazing

elephant: http://www.thingiverse.com/thing:257911
robot: http://www.thingiverse.com/thing:331035

OK? but didnt answer my question, should be more clear.
Do you need a special printer to make these moveable parts or will abs work?
Also how can you design these?