By bizn_fun 
To bring a robot to life, motion-activating components, or actuators, are essential. Generally speaking, actuators can either go in and out, or spin around in a circle, and there are many different ways of doing this.
Combining actuators with artificial bodies or limbs allows you to create things like a robot arm, a robot dog – or a humanoid.
If robots are to become more sophisticated, they will have to have more efficient, more precise and more intelligent actuators.
Relatively few firms today can manufacture actuators at scale with a high level of precision, and these components are still a long way from the incredibly engineered muscles that allow animals to move with such grace and efficiency.
A new generation of actuators could in theory enable the transition from stumble-bots to far more balletic machines.
“For a long time, roboticists have used DC [direct current] motors to make robots move,” says Mike Tolley at the University of California San Diego.
Such a motor is great if you want to spin a fan, for example, because it functions well at high speeds with low torque.
Torque is the measure of a twisting or rotating force that can move something, like a wheel, around an axis.
However, Tolley points out that humans don’t move the way fans spin, at all. “We want to be able to lift things, and push things, and do things that require a lot of force and torque.”
And, if a robot arm were to swing out towards you, for safety reasons you would want to be able to immediately stop it and push it back without harming yourself, reverse that motion instantly. For one thing, that requires a back-driveable actuator.
Simple actuators without this capability are a bit like manual transmission cars that need to be shifted into reverse.
“Another problem with today’s robots is they rapidly run out of batteries,” adds Jenny Read, programme director in robot dexterity at Aria, a technology funding agency. “Electric motors are terrible at that.”
Finally, really small actuators made using traditional electric motors tend to get too hot for their own good at such scales – another headache.