Pneumatic and Hydraulic Actuators?

I've been researching the construction of a rudimentary legged robotic platform using either pneumatic or hydraulic cylinders. After seeing
the system's complexity coupled with the difficulty and expense of finding parts, I can see why there seems little interest in this style of locomotion, especially among hobbyists. My knowledge is still limited, but the basic method of cylinder control seems to consist of solenoid valves, compressor tanks, pressure sensors, and a complex array of other components. This high level of complexity leaves the system error prone and awkward when fit into a space and weight conscious mobile platform.
Therefore, I propose a simplified numatic system in which the ports of a double action piston are connected to each other. Placed in the middle of this circuit would be a simplistic pump actuated by a servo or stepper motor. Since each actuator would be a closed system, the failure of one actuator would not necessarily cause the failure of the entire system. These small, closed circuits would be ideal for hydraulic fluids, and without the need of other components, the individual actuator would be simple and less prone to failure. However, a possible shortcoming might be the system's strength, which might only be as powerful as the actuator's pump, negating traditionally numatic's usual strength.
Overall, this is a fairly simple idea, so I'm sure someone else has thought of it before. However, I've yet to find any products matching this description, which leads me to believe that there's a flaw in my logic. Does this design seem reasonable? Why aren't numatic systems used more in robotic actuators? When will we see an affordable and robust linear actuator? What's the best way to construct articulated robotic legs and actuators?
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Hi Kris
Don't you immediately lose the advantage of hydraulics with your revised system? ie: the one big motor.
The Shadowbot tried seperate valves and pneumatic actuators and they seemed to wind up with a chest full of switches, no room for an integral motor/battery and seem to have given up. Brave effort though.
best regards
Robin G Hewitt
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