You don't have to drop the feed dogs. I have stippled on a Brother, Bernina and a older Singer that doesn't have a way to drop feed dogs. The main thing is to use a darning foot or a universal Big Foot. These let the material ride above the feed dogs when the pressure bar is lowered and the feed dogs actually help control your movement. You can set your stitch length to 0 if you want but it doesn't effect your stitch length, they are controlled by the speed you move your material in relation to the speed of your machine. If you move your material slow you will have little stitches, if you move it fast you will get big stitches. Practice until you have the right rhythm between the movement of your quilt and the speed of your machine. Practice does it. Good luck.
Stella