Set Up #2 - Pole Vector for the Knees

This post will talk about another type of constraint I used for this rig, a Pole Vector. A Pole Vector sets a constraint that allows the end of the pole vector to follow an object.

Fig 1: The Pole Vectors I used for the rig

I will now show you how I used this to help create the illusion for the knee, instead of using a polygon, I created a letter using the NURB Curves because as I mentioned in a previous post - NURBS do not appear when they are rendered.

I created my Pole Vectors using L and R letter curves, L for the left knee and R for the right knee. Once I had I chosen the positioning of where I want those curves to be (opposite the knee joint in both legs) - and scaled them down to the right size, I froze the transformations. Freezing transformations means that whatever the size, positioning (through transition to rotation) of an object - this will be the new default position. I named these curves: leftKneeControl (l) and rightKneeControl (r).

Fig 2: list of constraints and Pole Vector constraint highlighted

I then selected the Knee Control and the IK Handle I wanted the constraint on, then went to Constaint > Pole Vector (Fig 2).

Fig 3: Curves constrained to the IK Rotate-Plane on both legs

With these Pole, I can move them and the knee joints will then follow the movement like so (Fig 4):

Fig 4: Left Knee Control is moved and the left knee joint will then move in the direction of the Pole Vector

The knee joint will position itself in the direction the Pole Vector is going. 

Fig 5: Leg moved - note how the Knee is still facing the leftKneeControl due to the Pole Vector Constraint

That's it for this post, more to come very shortly.