Criteria: small, fast, zero force / load required, cheap.
I'm planning to build a very simple robotic face and I am not sure what kind of actuators I should use. I'd like the eyes to move back and forth about an inch but to be able to do so quickly (in under a second at least). I also want to open and close a mouth at a rate comparable to human speech... maybe a couple of times a second over at least 1/2" gap.
I'm aware of motor driven linear actuators, but they seem large, slow, and expensive... I'd need these to fit in a tight space. I've also seen the Nitinol actuators, but those seem to require a lot of power and behave unpredictably... My project will have to run on batteries.
Are there other options I should consider?