im pretty sure they use an attachment (i forget the name now)that looks very much like the attachment for ratchets that you can change the angle the head is at and still apply rotation. like if you have ever seen a double bass pedal for a drum set its what they use so u can change the angle of the pedals and still kick the pedal and have it rotate to the mallet. looks like this
heres the link
but i may be wrong so if i am someone correct me
Andrew