Hi! I know that I am a bit late but have not been able to read my site.
I read the reply that said to move your hands with your speed.
Anyway, somewhere out there is a youtube with a young woman who said that she puts something in her presser foot at the "right" spot to keep the needle going at a constant speed. I'm thinking of getting a cork that I can cut to size.
I haven't tried this as yet as I have not been able to get to my sewing or the board for a couple of months. You may have already solved this challenge but, if not, maybe this will work for you. Good luck
Yolanda Wood River