selection DC motor for robot

Hi,
i am making a robot which would be having a weight of not more than 10Kg.it is a four wheeled robot with chained differential drive and has two motors in all.i want it to have a good speed and a good torque.can any one tell me which motor will be best for it,and y that motor is best??

"Good" is a very loose term. I think your best start would be to ask yourself what the priorities are for your design, and come up with some numbers. What is the bot going to be used for? What does it need to be able to do?

Here's how I usually spec motors in a project:

1) Pick whatever speed you want to run at.

2) Do whatever math necessary to determine the torque you will need. This often begins as a more abstract idea like "I want my bot to accelerate to full rated speed in two seconds" or "I want my bot to be able to lift 20 pounds" or "My bot should be able to drive up a hill 30 degrees steep at 50% full rated speed."

A tip: The math does not need to be perfect, but it should be conservative. If you wind up with 20% too much motor, you're out a couple dollars. If you have 20% too little motor you're going back to the drawing board.

A good, medium motor, maybe 9-12 volts x4 will probably work.