XDog (2013~2016), as far as we know, should be the first four-legged robot driven by outrunner brushless motor (8108 Motor) in the world. Check XDog videos: https://www.youtube.com/watch?v=4ZPBL1zsLCg.
In the early 2014, the knee joint of XDog was tested driven by synchronous belt. The belt-driven video is as follows: https://www.youtube.com/watch?v=4QaANF4JWQs. But it was changed to link transmission afterwards.
8108 outrunner brushless motor have many manufacturers, such as T-motor.
For more details, please check our Youtube channel: https://www.youtube.com/channel/UCsMbp4V8oxzHCMdOUP-3oWw.