Those are all custom made cyclic gear motor servos. They are powered by high torque stepper motors. They cost a great deal of money, if you want a good start look at printing your own based on someones design already avail.

thanks, where to look, please?

The best place to start is probably the Open Dog project by James Bruton. It is ongoing so don't buy anything or start cutting materials yet. Here is the first video in the series-

https://www.youtube.com/watch?v=0BoPoWF_FwY

Also check out Mike's Robot Dog- https://www.thingiverse.com/thing:2793101

9g Nano Robot Dog https://www.thingiverse.com/thing:3145690

The Greyhound https://www.thingiverse.com/thing:73530

Dog Bot https://www.thingiverse.com/thing:6776

Or if you prefer cats https://www.thingiverse.com/thing:3054677

I think these are all works in progress or abandoned, or the designer has not released all code, but they are worth taking a look at.

Forgot one:

https://hackaday.io/project/157812-3d-printed-robot-actuator

These should get you started. Let us know how it goes!

these r super great, thanks.

Jason Bruton is the demi god of open source robotics. I guess you could build a simple one with EZB parts using a stack of servos. Probably have enough if you take SIX and mod him to form a robot dog. (Take 2 legs off and add one servo to each of SIX's legs) Then try and get him to walk, Actually could be an interesting project.

edit oh looks like Richard is all over an EZB robot dog, Excellent https://synthiam.com/Community/Questions/11705