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Best actuator options for a Biped?

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ErikY:
Would most people consider servos to be the best overall option for actuators for a Biped?

I have been reading a lot on this, and while very expensive, it seems like you can get the best combo of speed, power and control using servos.

Others I have been looking into are:

Linear Actuators

DC Motors with a built in feedback system, either potentiometer, encoder, other.

Pneumatic actuators

I would be curious to hear if anyone feels I am missing any other options, and what anyones opinions are on the subject.

One thought I have is for different types of joints, and different types of applications, perhaps different actuators may be best suited for the job.

jwatte:

--- Quote ---DC Motors with a built in feedback system, either potentiometer, encoder, other.
--- End quote ---

What do you think a servo is? ;-)

There are only so many ways of developing force that can be well controlled. Rotary motors, linear motors/solenoids, pneumatics, heat contraction wire, hydraulics, and direct electromagnetics are the main ones I can think of. Combustion engines are not great, because there's no good/immediate/robust way to directly control the amount of torque/force per-joint. (Slip couplings wear out, throttle response is sluggish, etc.) I guess you could use them for driving the compression in a pneumatic or hydraulic system...

Given those constraints, DC motor based servos are the best trade-off. Even so, there's a big difference between a $5 Chinese analog hobby servo, and a $500 robot servo like a Dynamixel EX-106. The robot specific servos (Dynamixel, Herculex, some specific HiTecs) are much better, having idlers on the back, digital feedback systems, etc.

ErikY:

--- Quote from: jwatte on January 20, 2013, 07:35:11 PM ---
--- Quote ---DC Motors with a built in feedback system, either potentiometer, encoder, other.
--- End quote ---

What do you think a servo is? ;-)

There are only so many ways of developing force that can be well controlled. Rotary motors, linear motors/solenoids, pneumatics, heat contraction wire, hydraulics, and direct electromagnetics are the main ones I can think of. Combustion engines are not great, because there's no good/immediate/robust way to directly control the amount of torque/force per-joint. (Slip couplings wear out, throttle response is sluggish, etc.) I guess you could use them for driving the compression in a pneumatic or hydraulic system...

Given those constraints, DC motor based servos are the best trade-off. Even so, there's a big difference between a $5 Chinese analog hobby servo, and a $500 robot servo like a Dynamixel EX-106. The robot specific servos (Dynamixel, Herculex, some specific HiTecs) are much better, having idlers on the back, digital feedback systems, etc.

--- End quote ---

I understand about the servos being DC motors :)

I probably should have put more verbiage into that one. I have seen some people do some really cool things with DC motors, making some very powerful joints at a fraction of the cost as a powerful servo. I was really factoring cost into the equation as well, as the high end servos as you mention are extremely expensive, ecspecially if you want to get any significant DOF in your Biped.

I also was throwing stepper motors into the DC motors category, which was probably a bad idea since they do behave quite differently.


idee17:
I have various dynamixel servos in the passed and have had very good experiences with them just remember that they use half-duplexed communication instead of the traditional PWM signals. This way you can get feedback from them.

~Idan

ErikY:

--- Quote from: idee17 on January 24, 2013, 03:44:18 PM ---I have various dynamixel servos in the passed and have had very good experiences with them just remember that they use half-duplexed communication instead of the traditional PWM signals. This way you can get feedback from them.

~Idan

--- End quote ---

I have some AX-12A Dynamixels.

The functionality is very cool, no doubt.

They are very expensive however, and the cost of using them adds up quickly, but that really goes for any quality actuator I suppose.

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