I created a new version of the quadruped. I recreated all of the parts for add configurations. Now, the quadruped has AX12/AX18 configurations (it is easy because the motors have the same design), I add the MX28 configuration. So it is easy to choice the quadruped that you want 
AX18 :
MX28 :
I also created an hexapod with configuration AX12/AX18/MX28.
AX18 :
MX28 :
I added the raspberry-pi 2. I still have to add battery, maybe camera (pan-tilt or not) and the toso for putting Poppy on the quadruped/hexapod.
So with the assembly, you have quadruped with AX12/AX18/MX28 configurations and hexapod with AX12/AX18/MX28 configurations.
For now, it is impossible for me to test the mechanics because the motors are too expensive but I will continue to improve the all of the parts(reduce weight,ameliorate the design…).
If you have ideas to improve the creature, I take it and the contributions are appreciated. I didn’t put the part online for the moment, I try to put the first version this week. 