How to make a robotic hand with hydraulic/pneumatic syringes?

Here are some ideas:

http://www.vtnews.vt.edu/articles/2009/10/2009-738...

http://www.scientificsonline.com/bionic-robotic-ha...

These use articulated fingers that have elastic ligaments or springs to cause them to curl and grasp or return from their actuated position. The curling is just the way the levers are oriented. They are nowhere near as good as a human hand, but still useful learning. The first link seems to use air in internal cylinders like syringes, that push or pull the fingers and cause them to curl around the joints. It needs a high level of skill to make the mechanical parts for this.

This link shows how someone used a bicycle chain to get flexible joints. Soinds like a brilliant idea to me.

http://www.instructables.com/id/DIY-200-Robotic-Ha...

A more complete hand uses ligaments that go back up the arm, more like the human hand. The actuators are then hidden in the arm. The simplest actuators would still use some sort of spring return. This is more suited to the idea of using medical syringes as actuators. I would be inclined to use water not air, as it provides a little lubrication, and less dramatic if anything breaks. Leaks are a problem though. This link shows the basic idea:

http://www.sciencebuddies.org/science-fair-project...

An actuator with a position feedback is always going to be better. This is what pulls the strings (ligaments). This is called a servo system. The electric actuators used for model planes are a low cost way of getting this controlled movement. They can be remote controlled (by radio) or controlled directly by a simple micro-controller like an Arduino. With proper design an actuator can close with a measured force, important if you intend to pick things up. Human fingers have position feedback, as well as touch and force sensing. Some pages about radio control servos for model planes:

http://en.wikipedia.org/wiki/Servo_%28radio_contro...

http://www.pololu.com/category/23/rc-servos

These have an arm that can moves through about 90 degrees to the specified angle, and are used for moving rudders etc. on the planes. They can push and pull, and resist a force that tries to move them off position.