Ha, I bought a Grand Carpet Mill and couldn't get any of my dogs to run on it. You're better off buying a used electric treadmill. Not all dogs take to a carpet mill because it's self-powered and some see no point. Check out some pit bull message boards for info. A lot of folks with that breed have plans for building carpet mills.
I don't think I would pay someone professional to teach my dogs to do something they don't want to do. They're dogs, not robots. And yes, I know many people have no trouble getting their dogs to run on a carpet mill. But I'm not going to force mine to do it if they don't want to.
I doubt anyone here can help you with pictures of the roller mechanism of a carpet mill. They only place you're likely to find that is on a pit bull message board since that is the main breed that carpet mills are used for.