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Skis part 2: Cycling the skis
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By Bernard Lebel

In the previous tutorial, Creating the Skis, we saw the construction of the skis. Now we will animate them in a looping walk cycle.

To animate the skis, you have to use translations over the ankle circles and rotations for the ski bones. The skis, as well as the other constraint objects, are completely independent from the rest of the character. So wherever you move the ski the corresponding foot will follow. The only exception is if you SRT GOD (the supreme null) in branch mode. The skis will prevent the feet from sinking in the ground.

PAGE ONE - Initial setup - Understanding the hierarchy - How it is keyframed

1- Initial setup

We will animate the walk cycle over 40 frames. This gives a slightly slow movement, but it will allow you to understand the mechanisms. So put the start frame at zero and the end frame at 39.

Open the rig_final scene in the provided database. Activate the loop playback (the L button under the start frame).

2- Understanding the hierarchy

We will now examine certain area of the hierarchy in order to better understand the technique.

GOD: On top of eveything, you have a null called GOD. Like it has been stated previously, this null is master of everything. This null shouldn't be animated in a single shot. It it better if it stays untouched. It becomes relevant to move it only if you want to move your character somewhere in another scene. The only exception to this rule is if you want to apply a lattice the whole character. Because of the various bones and constraints, it will work better if you apply the lattice on GOD. GOD is parent of CUBE and CONST.

CUBE: Immediately under GOD is CUBE. You can see CUBE easily in all viewports, because it is a big black cube. This is this object that will SRT, whenever the character moves. CUBE allows to move the character without the constraint objects. In the walk cycle, it he who moves the character from one place to another and vertically. This is also on CUBE that you apply the rotations of the body. CUBE plays the same role as the hips.

BODACT: Immediately under CUBE is BODACT. BODACT stands for BODY and ACTOR, and is the parent of the nulls of the same names. BODY serves as an intermediate between the main components of the character (the envelope and the rig) and the objects that controls their SRT (CUBE). In the scene rig_final, you can see there is no BODY in the hierarchy. In fact, there is no envelope at all. If there was an envelope, the top null would have been BODACT. So for now BODACT is only parent of ACTOR. You shall never put keyframes on BODACT. It occupies the exact same position as CUBE.

ACTOR: Immediately under BODACT is ACTOR. This is another null, but this time being the parent of the whole rig. Again, you should never animate this object.

CONST: This null, immediately under GOD himself, is the top parent of all constraints objects, and it is only utility. You shall never keyframe this object.

So in the end, the only objects that you will animate, in this tutorial, are the ones selected in the image below, namely: the wrist cicles (wrist_L and wrist_R), the heel circles (heel_L and heel_R), CUBE, and the three bones of each ski.

3- How it is keyframed

Finally, before animating, we will briefly see how we will keyframe the different parts.

CUBE will be animated with local rotations XYZ but explicitely translated locally in Y only.

wrist_L and wrist_R will be animated with tranlations (paths).

heel_L and heel_R will also be animated with tranlations (paths).

All of the ski bones will be animated with rotations on Z axis.

Let's now quickly examine the mechanism of the ski before animating it.

Select the first ski bone (ski_L_bone1) and rotate it in Z axis. You will see that the whole feet moves up, but the heel stays almost where it is.

Undo this. Select the second ski bone (ski_L_bone2) and rotate it in Z axis. The foot moves up again, but this time the toes'end stays on the ground.

Undo this. Select the third ski bone (ski_L_bone3) and rotate it in Z axis. This time only half of the foot moves, all the toes stays on the ground.

Now you understand everything that you need and we can go on with the animation!

Next: Moving the heels.