You have no control over the current directly, its more to do with how much current the lipos/batts can deliver before they become over-drawn. At this point, they will heat up rapidly, swell up and in some rare cases catch fire, often taking the esc with it.
This is why its important to use a lipo/batt that can deliver enough current for what the motor & general setup will likely draw. Castle recommends a minimum of 100amps I believe, so you should aim for about 100-120+, the more the merrier (my setup can deliver about 200amps or more, so the lipos never even get warm, staying well below the 120*F max temperature that is safe for lipos).
Its covered in my Tutorials and Emaxx/Erevo FAQs on my website, well worth having a read, or to put it another way, read it or else....
http://robotwars.00server.com/emaxxfaq.html
