For Drivetrains (& more);
There are two very awesome drivetrain calculators out there;
JVN's is more complete and offers a lot of information (graphs of motor load, current draw, speed, position, etc...)
Steve Judd's is made for combat robots, but I asked him to add the two CIM motors to it. You just pick the motors, wheel size, weight, etc... (same stuff as JVN's) and it will give you a quick estimate of speed and current draw. Not as much information, but a lot easier. I
t is under the "tools" section of his site (called torque/Ah calculator).