Take a look at my shortarm setup. I have a picture of how my pantograph system works. My shelf is over the top of my frame, but many have a shelf down behind the machine. Both types use a laser light as a stylus to follow the pattern.
Here's my posting:
http://www.quiltingboard.com/t-138660-1.htm
I find it a very effective and efficient way to do quilting motifs. Easy to follow and you get good coverage.