Hydraulic limbs

[Arislan]

Can someone tell me if only one single hydraulic pump is needed for all limbs in a biped? I'm studying some theories on bipedal bots, and one idea that occurred to me was to have a "muscle" system of hydraulic cylinders electronically controlled by hydraulic valves. I read this article:
http://www.intelligent-systems.com.ar/intsyst/robby.htm
and it gave ideas on a pneumatic system. The builder chose pneumatics because of the overall weight of the robot.
But I'm uncertain how many pumps would need to go into this design.  And also, what hydraulic valves are available. But if I found out there were electronic valves, I would look into it and try to design a sample limb.

[Admin]

Can someone tell me if only one single hydraulic pump is needed for all limbs in a biped?

Theoretically possible, yes. But Ive never seen it done very well.

This is because they are generally weak, compliant (meaning not accurate), require huge/heavy air compressors, and from a controls perspective its a nightmare . . . Not too different from muscle wire, I think . . .

If you want to use them, do your math first 

[gamefreak]

couldnt you use a solonoid?

My idea would be have 1 solonoid for each leg and have them move out to create a stepping motion, I dont know much about solonoids but if you can make it move in and out slowly then with servos to move the legs back and forth then you would have a wobble/walk, If soloniods dont work slowly but shoot out rather then you could try a cam pushing a cylinder down and a spring to pull it up.(just like a soloniod but have a servo control the cam)

Hope it helps

[Shags]

I too have considered using hydraulics for a robot,  I looked up micro solenoids, micro values (like they use in medical equiptment)  etc.  It is doable but even the larger sized hydraulics and values can require a bank roll.  You can definitely move a lot with hydraulics but to get down to the size you want you are going to be spending thousands of dollars.  I have since given up on the idea (at least until I am rich)

[gamefreak]

what about the air muscles? They are pneumatic, but they work by filling a bladder covered in a flexible mesh, the mesh is securly connected to either end of the bladder, so that as it gets wider it also contracts, Now I dont think they have hydrulic "Air Muscles" although it seems to me like it would be a simple switch.

[ed1380]

it'd be the same except for the reservoir tank and the valves. also the exces liquid would have to be sent to the reservoir tanks instead of just being exhausted