Hi, I have not done more tests yet but, i can tell you is I use a Futaba Servo S3003, working at 5V with 3,2 Kg of torque. With this power approximately can be pulled a 17% of the string maximun lenght.
To improve this value, we should make lighter vertebrae, use flexible wire instead of string (there are much friction now), and of course increase the power. And i want reduce the wheel radio (I have do more tests).
This is the first prototype, but with a desing upgrade, could catch objects, this
idea it may be interesting.