Sounds like a good suggestion, thanks for the help!

I'm sorry if I was unclear.  What I am looking for at this juncture are motors, but I don't know what kind of torque to look for (as torque seems to be a defining factor, and at the moment I am not overly concerned with power consumption).

The casters I mentioned could be something like this: http://www.sparkfun.com/commerce/product_info.php?products_id=320

Just to throw out some numbers, I suppose it could be assumed that I want to use 2'' wheels and that a movement rate of 60 RPM is ideal.

If there isn't a simple equation somewhere that will give me the nice number I want, I may have to go with your idea jack (thanks!).

EDIT:

Wow.

You must have finished crafting that just as I made my post, which seems to answer some of the assumptions you made. Thank you very much for those equations! This will be very helpful!

If we were to assume the world is perfect, and the only friction my bot experiences is from the wheel's contact with the ground, where would be a good place to start?

What's a good way to determine how much weight a motor with a given torque can carry?

Given a basic (7''sq) setup:

_____
|       |
m     m
|       |

(where 'm' is a motor, with casters at the corners to support weight)

With, say, 5 lbs of weight evenly distributed across the top of the bot, how much torque would I need to move it?

The sensor's product page: http://www.maxbotix.com/MB1240__XL-MaxSonar-EZ4.html

(The forum wouldn't let me post a link in my first post)

For my current project, I'm using a XL-MaxSonar-EZ4 MB1240 (see next post) to gather range measurements, that I send to my PC with a Duemilanove. My problem, is that the sensor seems to be sending its pulses out at an odd angle. I found that in order to get an accurate reading from the sensor to a target of known distance (with good reflectivity, and in open space), I have to tilt the sensor up almost 45 degrees. Has anyone else had this problem?