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A brushless motor with an encoder and a feedback loop is a servo. It's just not a crappy integrated RC model servo motor assembly.

The (ab)use of the term "servo" is a major pet-peeve of mine.

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Sure. I should have written "rc-servo". But in this context it was not ambiguous and the point stands - anything that uses rc-servos is a dead end. Personally I'm also skeptical of series elastic actuators - it seems like a half-assed solution where the proper solution is to embrace full direct-drive digital control of electrical <-> force conversion.

The "problem" I've seen with a lot of walking robot projects is, where an RC car needs 2 motors and a quadcopter 4, most "interesting" walking robots need 12 - which means they instantly have to start making compromises due to cost and weight.

This robot ain't exactly large - but it's already needed $450 worth of Dynaixel AX-12A servos.

We have a hexapod (18 Dynapixels) at work ... apart from giving demos to visitors it's not used at all. Gait patterns and (inverse) kinematics are a solved problem ... dynamic gaits are becoming more mainstream now, but those require motors that are reasonably backdrivable. Maybe the Dynapixels can be configured to do that, but I think the high gear ratio will prevent that.

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