- It’s the equivalent of syringes filled with fluid, and as one empties, the other fills.
- Hydraulics is a completely different system than servos and it’s hard to compare the two. The Owi kit uses microhydraulics, whereas more powerful robots use (for lack of a better explanation) “real” hydraulics because of the forces involved. Hydraulic force is linear whereas a servo’s is rotational. To compare the two you need to understand the concept of torque (force times distance). Each hydraulic actuator would still need an actuator. Small hydraulics = small forces. Note that the force you get out will be slightly less than the force you put in.
Owi makes a “hydraulic” robot arm which you can play with to see the results: https://www.robotshop.com/en/owi-hydraulic-arm-edge.html - Worm drives are not required. If you look at Owi’s system on the arm, you can push fluid into the cylinders however you want - even servos would work well. However, whatever you use should ideally have position feedback to prevent the motor from “over-pushing” or “over-pulling”.
- Hard question to answer - in theory, the tube can be quite long without any losses since you’re using force to fill and empty cylinders.
- RC servos seem easiest, but you’ll really need to compare the rotational torque which the servo can provide to using it to actuate a hydraulic cylinder. You may end up getting significantly less force out of a hydraulic system which uses the RC servo than the RC servo produces by itself.
- Normally not, but that doesn’t mean it’s not possible to create a system which is lighter. See the section below which better explains “proper” hydraulics.
- Too many factors at play to give an easy answer here. You will really need to understand the concepts of torque and converting pressure to a force. Do the exercise on ONE joint.
- Not sure what you mean given that the hydraulic force you are referring to is linear rather than rotational.
So, a bit about hydraulics: there are many reasons why you don’t see hydraulics being used in almost any small to medium sized robot, let alone industrial robot arms - they are complex, expensive, prone to leaking and very heavy. A basic hydraulic system would consist of:
- Reservoir (contains enough fluid to fill all pumps, and a bit to spare_
- DC pump (powerful enough to fill several hydraulic cylinders at once without significant losses in force to each)
- Hydraulic cylinders, each with their own actuated valves
- Battery pack to power the pump
The pump alone is normally really heavy, making a hydraulic system quite impractical for a robot which needs to be lightweight. The requirements of adding a liquid reservoir and a separate battery make it even less practical. Since each cylinder still needs either a solenoid driven valve or its own DC type actuator, the complexity of the electronics just gets worse.
This having been said, for a full scale humanoid robot, you might consider either geared servos, semi-pro servos or DC linear actuators, or a combination thereof.
https://www.robotshop.com/en/actuators.html
https://www.robotshop.com/en/servo-motors.html
https://www.robotshop.com/en/smart-servo-motors.html
Consider the M100RAK which is roughly the size of a real human arm and uses geared 785HB servos:
https://www.robotshop.com/en/robotshop-m100rak-v3-modular-robotic-arm-kit-no-electronics.html
Adding additional degrees of freedom and/or a gripper will obviously reduce the payload.
A full scale exoskeleton system which is used to provide very high forces may have to use a hydraulic system, but most still use DC motors, and the more expensive ones use “torque motors”.