Choosing DC motors is not simple as it says. You need to calculate the velocity, voltage, current and the most important is… torque… I’ve some experience about choosing the DC motor for my robots. Sometime my robot going wild with high velocity motor and low torque motor. Sometime my robot is to slow but the acceleration is very good, so easy to be controlled.
If you build a robot, you must pay attention about this tutorial.
Go to this page for the tutorial.