Re: Mechanical linkage of front legs to back legs.
I have thought of that, but I don't see a way to make it look really good. A friend once made a passable centaur by making a foam horse body, and just using string to attach the rear legs to hers. It looked ok, but was too “fake” for my tastes.
There is also the problem of proportion. The front legs vs upper body size of most centaurs (that I like) aren't even close to human proportions. Either my legs are way too long, or my upper body is way too short.

From: Bruce Mai
We've seen someone do a centauroid moving the legs by a nylon string tied opposite to the front legs, but it seemed only partially successful. We're working on sort of the same mechanical problem. The original electrical solution just seemed too heavy (almost knocking Nora off her feet because of the battery, motors and the wooden framework). So, we may try an aluminum framework next time and use a system of pulleys..