Mark, I would also discourage you from using the 5645 in the Roo. I had a lot of problems with the 5645 and have been on the phone with Hitec about it. When the "rubber met the road" the Hitec manager questioned why we weren't using the 5945? He gave me the impression that he personally would not use the 5645 on any high dollar performance aircraft. I never did get an answer to why my 5645s were faulty. The 5945s use coreless motors the 5646s do not.