Do you mean the way the arm goes up and down? If so, use this (Just put it in bottom of file and change the name):
function YourImage::onPreFire(%this, %obj, %slot)
{
%obj.playthread(2, armattack);
}
function YourImage::onStopFire(%this, %obj, %slot)
{
%obj.playthread(2, root);
}