Reverse Foot Lock

The reverse foot lock is a set up of joints which drive the movement of the foot. It makes it easier to move and position the foot rather than having to position each joint. It's called reverse because of the way that you order the joints, in the opposite way to when you make the normal foot joints.

To prepare for the reverse foot lock you need to make IK handles for each joint in the foot. Double click the IK handle tool and choose IKSC solver  in the drop down menu. Then make handles from the ankle joint to the ball and from the ball to the toe joint.

Now using the joint tool make joints as shown above. Start with the joint under the ankle in line with the ball joint. Create the joint here then at the toe and then backwards to the ball and finally the ankle.

Now attach the ankle,ball and toe of the reverse foot lock to each IK handle by first selecting the handle and whilst holding shift select the joint. (this is easier if you hide the layer with the actual foot joints on so that you don't select the wrong one.) 

Once both are selected chose parent from the constrain menu to parent the handle to the joint. 

Parent the handles starting with the ankle, then ball, then toe, once this is done you should be able to control the foot using the joint at the back under the ankle.

The foot should now move as shown.

Creating a Controller .

To be able to easily select and move the leg using the reverse foot lock joint we can create a controller which is larger making it easier to select.

Create a NURBS shape and move it to under the foot as shown in the diagram. If you hold the V key and drag the shape it should snap to the joint. When it's in the right place freeze transformations so that you can easily get the joint back to the zero positions. First select the shape and holding shift select the reverse foot lock by the back joint. 

Select the constrain menu and then point. By constraining the NURBS circle to the joint it can now be easily selected and moving the circle moves the leg.

Pole Vectors

To create a pole vector first create a NURBS circle just in front of the knee joint. Now freeze transformations and select the IK handle from hip to knee and holding shift select the NURBS circle. 

Select Pole Vector in the constrain menu. A line should appear from the hip to the circle. The pole vector should now function. You will now be able to move the knee from side to side without moving the foot and you'll be able to position the knee separately from the foot allowing for more exact positioning of the leg.