How to calculate motor torque needed?

Hi! I just found this website through Google by trying to find gear boxes, and I have a question about which gearbox/motors I need to buy.

I’m trying to build a balancing robot, which will look something like this:

I made a typo in the image, “cs” I meant as “cg” for center of gravity (I’m putting the batteries in the middle).

I’m planning on the robot weighing about one pound, maybe a little less. My question is, how to I calculate the torque needed for the robot to move at about 6ft/sec (my estimation on how fast it needs to move to right itself) at a 20deg (I don’t want it leaning more then that) angle?

I’m planning on using these tires:

I’d like to buy one of the gearbox/motor combo sets off this website, but I don’t know how to calculate if they will provide enough torque and speed.

Thanks for the help!