some answers to your questions:
what kind of motors are used on each wheel?
I believe that most teams use the drill motors and/ or chips to drive the wheels. but this all depends on the set up. If your crab drive is going to have one constant chain moving all the wheels at once then it doesn't matter what motors you use for each wheel as long as they are geared correctly to match output speed.
how are they geared?
well besides making sure the wheel speed is the same on all the wheels, the motors are normally mounted above the wheels and the gears go down through the wheel casing.
how are they configured?
This all depends... some teams have a 2 wheel crab drive with omni wheels, some have a 4 wheels system where all the wheels are physically timed together, some teams have 4 independent wheels and are programed in sync. The configuration will depend on a few things, 1) what motors you have in the kit and which ones are most simple to match speed on, 2) which type of system you want to have, 2 wheel, 4 wheel, etc. 3) and it also depends on your teams resources, there can be alot of custom parts that have to be made for specific types of systems and what equipment your team has access to might determine the type of drive you build
What motors are used to turn the wheels (either 1 motor for 2 wheels, or 1 motor for 1 wheel)?
I have seen the Fisher Price, globes, and windows all used. the globes are usually the ones when it is each wheel turning on it's own, the FP and window are used when there is a system moving more then one wheel
If you gear the motors up or down, what size sprockets are used?
this all depends on your speed and for the most part you will gear things down, putting over 6500 rpm (chips) or over 1400 rpm (drills ) isn't usually a good idea and the size of the sprocket all depends on how much you want to gear them down.
Anything special that we show know about your system (angled gears, strength of the chains, speed, power, weight, unique programming)?
the only thing that I can think of is that crab drives need to be carefully planned because of how involved they can be
and most importantly, what kind of control system is used (what does each joystick do)? there are a number of things you can do., but I believe the most common is using one joystick where a hard left, turns the wheels horizontal, the same as a right turn.
Code:
-- --
| | | | joystick forward /back
-- --
____ _____
| | | | joystick left or right
------ --------
those boxes are wheels sorry for the crudeness
I hope this helps.... I know that there are some good pictures of crab drives in the gallery and you can learn a lot looking at what other teams do....good luck