A loose grip on the bat and spaghetti arms. That's how I learned.
I was a baseball player and always kept a tight grip and very tense arms and wrists and always had complete control of the bat. Always hit the ball decent, but never was anything spectacular.
I always kept hearing about "whip" and always thought I knew what it was but never could figure it out.
I eventually found out, it's ALL about the whip. In my opinion, the only time your arms should be straight is at point of contact.
This may seem crazy, but that Pumpkin Chunkin' crap they do up north basically works on the same laws of physics. In this video,
at 2:45 is a quick simulation that is a great testament to this. Imagine the white dot in the middle is your waist, the white line is your arms, and the red thing is your hands/bat. When the red thing catches up with the white thing, it's haulin a$$!
It's pretty uncomfortable and awkward when you first start trying it, as it seems like you have virtually no control over the bat. But in time, the bat control will come.
As a disclaimer, I'm no pro by no means, but I have great mechanics. I can hold my own, considering that I basically put forth 0 effort into training, BP, etc.
Hope this makes some sort of sense!