So you built a robot controller board - what do you do now?
This page tries to make you think about the issues you need to consider when building the rest of your robot
Normally you choose batteries and motors together - we have a couple of simple limitations to make sure we don't damage the motor controller: minimum battery voltage ~7v, maximum voltage ~24v, maximum current 2 amps. If you find your power controller getting too hot to touch you may be overdriving it, or maybe it needs a heatsink.
So find two DC electric motors - you will need to find geared motors (or a twin set with gear boxes) otherwise your robot will go too fast - a hundred RPM or less - not thousands of RPM. Here's some links to possible sources:
There are many others - please share what you find and what works for you?
Choose a battery with a voltage to match the motors. If you choose to use AA or even D sized batteries they wont last long, and they'll cost you a lot, rechargeables will save you money in the end - you also need to choose batteries that can provide enough current to drive your motors. I like miniature sealed lead acid 'gel cell' batteries, but nicads and lithium cells will do too.
I've had good success with 6v motors and "6v" gel cells (really 7.5v when fully charged)
Find some wheels that fit the axles on your motors.
Servos are smalled geared motors that can be used to position something - move a sensor to point at something, or operate a gripping mechanism - cheap servos can be had for under $10 - you can drive two servos from each sensor port.
You could also build a vehicle with a single driving motor steered with a servo.
Which robocup event do you have in mind? choose the sensors you need and think about how they will have to be mounted - line followers need to be near the ground, range finders up in the air or mounted on a servo etc
Now you know what you are building how will you put all the pieces together? A flat plywood base plate is a great place to start - mount the two drive wheels and add a send pair of wheels or a third wheel caster. How will you attach the motos? stop them from revolving (nuts and bolts? cable ties?)
If your robot is going to go up and down ramps make sure you have enough ground clearance.
Batteries are heavy so mount them as low on your robot as you can, but remember you will want to take them out and charge them. Mount the electronics so you can get the USB connector plugged in, mount an on/off switch so it's easy to reach.