Hey,
I dont know about you, but i often get cramp when im tierd, and i put my muscles in a certain position.
I say try 3 things:
Move your kit around so that cymbals are closer/easyer reach.The positions you have right now could feel comfortable, but your muscles may think differnently, and it could be those positions where you are most prone to getting cramp.
Excercise before you start drummingDrumming can be like a sport. It is quite a physical thing to do, and like anything that puts strain on your body, you need to get your body prepared for it before you start. This can be from waving your arms in circles, jogging, or just slowing doing rudiments and then gaining speed.
Drink moreApart from having low levels of salt, low water levels cause cramp. So just make sure you drink.
Enjoy
