I think we should start with a little info about this tutorial. I created a rig for a character in a group project I was doing in a class, and once the rig was completed and we looked at the 3D animatic, we noticed there was a problem with the hand rotating around; double rotation in the forearm. We searched on the internet to try to find a solution to the problem, but since we couldn't we had to tackle it ourselves. My teacher wouldn't let me stop until I reached complete fetal position, so let's get down to how I solved this problem.

For those of you who don't know what double rotation is; it's the rotation of two bones inside your forearm--the radius and the ulna. As you rotate your hand those two bones rotate over one another to allow us such motion.

image from www.artofpracticing.com

Now, with Max, the Biped system has this option checkable to solve this problem, but for those of us who like using the Bones system to setup our rigs, this tutorial will help you realize this concept if you haven't, or solve it if you have run into this problem. I just want to make a quick note that I learned how to rig characters using bones by using the book, Model, Rig, Animate with 3ds Max 7 by Michele Bousquet. Very good book to help get the beginners started and what not. If you don't have double rotation setup up in your rig, you'll receive a twist like that in the following photo. It's a playblast of the animatic where we noticed the problem first.

  lna. As you rotate your hand those two bones rotate over one another to allow us such motion