I've got the key

I went out to practice serve last night, trying to apply all my newfound knowledge after doing video analysis. It was going OK but not great; serves came out better if I tucked my left arm. Then I had this small revelation: when the racket is in its highest position on a wind-up, pointed straight up, there's sort of a natural lull in the motion. If I time lowering my body for that moment, then as the racquet comes down, I'm pushing up and it comes out great, and the ball spins in effortlessly. I'll need to look some more at clips to refine the timing, but I think I got it.