An important fact about your robot is the speed of the drivetrain. Having said that, how do I calculate the speed of the drivetrain?
Roller chain is usually used in robots that we build for the FIRST Robotics Competition. #35 roller chain is the standard chain pitch that
Here is a scan of a SolidWorks document that has 14 tips for designing robots using CAD. CAD – 14 Tips to Design Robots