As long as you can attach it to the axle securely it will work. Mine is moving at a pretty good clip. If it came apart it would cripple me and the dog.

Although it is a circle, the larger the diameter the more the dog is going in a straight line, if that makes sense. A smaller circle he is in more of a turn, sort of contorting his body and it will "run out from under him" and he will skip a step to catch up/get his feet under him and that could lead to an injury nail/pad etc..etc.. The larger the table the easier it is to center the dog on a good running line.

I am by no means an expert. I saw one long ago, then again a couple years ago. I built one just because. I can see where 16' is better than 14', and bigger than 16' is even better. It took a dog or two to get the hang of what it was doing and with some insight from CYJ I think it is doing a pretty good job for the dogs. I have learned that shorter sessions with changing speeds works best. But I do think the key factor is the free-ness/smooth-ness of the table. Each dog would have to be fine tuned to each table. I doubt there is a blanket work method that would cover all dogs on all tables. But that is just me. EWO