(note : this method is for MAX 3, version 4.2 has a much much better system !.)

This tutorial is designed to take you very quickly through the process of boning and setting up a figure with IK ready for animation. Note that this set-up is simply for the legs, and represents only one solution for wiring a figure. Work your way through and then try to expand and experiment with the techniques.

1. Build your character.
There are a few requirements for this IK set-up to work, first off don't place a joint dummy between the upper and lower leg, and secondly make sure you reset the transformations and scaling for your objects before you bone them. Also it's a good idea to collapse the stacks of your objects to speed up MAX a little.

(Note that at this point your shouldn't join any objects together in a hierarchy.)

Now link together each leg by itself in the following order :-
ankle dummy to lower leg to upper leg to hip dummy. (do not link the feet at this point)

2. Adding in your bones.
In the create panel you'll find bones listed under systems, click on 'pick root' and select your hip bones one at a time. You should now see a series of yellow bones running the length of each leg.

You'll find if you select the end bone and move it around the leg should follow. However the rotations will no doubt be all wrong, we'll fix that in the next stage when we start to apply restraints to our IK chain.

(remember to UNDO any movements you make before you resume work)

You'll also need to UNLINK the ankle dummies from the chain for now, as we'll be using those later to control the feet.

3. Changing the IK parameters.
For each leg select the last bone and go to the motion panel. Change the iterations to 100 for each and the end time to 4000 (this is the last frame that IK will work at, so you can input any number you need in here).

Also select 'Lock Initial State' which will tell MAX that this is your starting positions incase the character becomes all twisted.

4. Adding controls.
Also in the Motion panel for the end bones you'll find a button marked 'End Effecter Parent - Link' press this and choose the ankle dummy. Repeat this process for the other leg.

Now attach the ankle dummies to the feet and attach the hip bones to the hip dummies. You can try moving the hips and the feet around, and you'll see how you can control the legs.

(remember to UNDO any movements you make before you resume work)

4. IK constraints.
Now the only real problem is that the legs rotate erratically, and in directions which in real life would cause some serious damage !. So the last major step is to constrain the joints so they can only bend the way we'd like them to.

Go to the Hierarchy and then select the IK button. Change the position weight of the last bone in each leg to 200 (this should help prevent foot slippage)

If you scroll down you'll find the rotation limits panel, this may involve a small amount of trial and error to limit the knees so that they can only bend in one direction (it was the X axis for me).

When you've found the correct axis make sure to check the limit and spring buttons, and change the spring to 5 and the tension to 0.3 (this will prevent the leg from locking up).

You'll probably find that the leg still rotates and bends the wrong way. This is because the upper leg is allowed to bend in the Y axis, so turn this off in the rotation limits panel.

Now the last constraint is to stop the knees from bending the wrong way round, you can set this from within the rotation limits panel again (choose the axis within which you're allowing rotation). And limit the rotation from around 170 to 3 (or-170 to -3 depending upon your orientation), to help you you'll see a small orange arrow showing the range of movement allowed

.Ben Cowell 2001