Another hardware option is the BaneBots p80 transmission with a CIM motor.
http://banebots.com/pc/P80K-S4/P80K-443-0005
They come in a variety of ratios.
Like an earlier post, I would recommend relocating the motor/transmission from the pivot point. Sprockets and chain would be my approach.
If you have or can get a drive transmission, that might be another option with reduction gearing.
Dave
Mentor 2976