I have five small DC motors with gears on them already I want to design one big gear for four of them, but when I bought these motors they came with no specs with them, I tried contacting the manufactuer but they could not help. Is there a way to calucate the size of the pinion gears without any special equipment(all I have is pencil, paper and ruler), they are involute gears. (I know math pretty well so through equations if needed).