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Author Topic: Questions about robot actuators  (Read 1600 times)

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Offline ganvarelTopic starter

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Questions about robot actuators
« on: October 16, 2014, 10:26:14 AM »
Hi to all, I'm new to this forum ( but not to robotics ). I'm no pro but just a hobbyst, however ( being a programmer ) I have a basic knowledge of physics and other stuff necessary to build robots.

I have built some simple robots ( some crawlers and a bioloid, plus some wheeled robots ) and I have always used dc motors and servomotors. But I'm trying to build something more interesting, a two legged humanoid the size of a child to experiment with AI and machine learning in robots.

I have made my homeworks and researched a bit the topic of actuators. What I have seen is that hobbysts use servos ( obviously ), but pros use custom built motors, linear actuators with dc motors, linear motors ( the ones that work like the maglev ), pneumatics, hydraulics, and so on.

For various reasons I don't think that hydraulic or pneumatic actuators are a good practical choice, so the only remaining realistic actuator type is the electric motor.

I have seen that the universities and labs around the world use frameless dc brushless motors ( torque motors ) + harmonic gears or custom built linear actuator with springs and other mechanisms to implement compliant joints.

But there is another type of electrical actuator, the so called linear motor ( also called direct drive linear motor ). I'm talking about this thing https://www.youtube.com/watch?v=SHTvv47Cs-E

This type of motor is fast, has great peak force, no bearings, pulleys, gears, etc... It seems a really good choice, but no humanoid or legged robot in existence uses them. Why? Is there a catch?

Offline Kohanbash

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Re: Questions about robot actuators
« Reply #1 on: October 19, 2014, 04:40:37 PM »
I am not positive why they are not used.

In most of my past projects we have used brushless DC motors with various types of gearing. I think one advantage to this approach is the ease of using your own gearing to modify speeds and torques.

I have used frameless motors before and they are very tricky to get right. You need to be very careful with the mechanical design and assembly to get the rated performance specs of the motor.
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