For your modeling pleasure, here's
the BaneBots MP-36064-545 64:1 Gearmotor with the Fisher-Price 9003 motor in Inventor 8.
Please read the Read Me file in the zip before you use it. I don't have any of their other gearmotors to see how much the body length varies with the gear ratio, but all you'll have to do is change the extrusion length of the Body.ipt to suit other ratios.
If you plan to use this part in the real world, check out
the BaneBots thread for application info (like how to cut the FP armature to the right length).
