Notebook Lesson 14

  • Yonseo Rigging Kit for Modo

Inverse Kinematics Legs

Making the Leg Control using IK

With inverse kinematics we are working with tools that work automatically for us. It's a similar process to creating locators and adding modifiers only here IK does the work. We simply have to assemble.

1) First Enter [Setup] and select 3 bones in our leg.

Now click [apply IK] and a pop-up message will appear. This means the software has found that our leg joint rotations don't match, so the software will fix this for us! click ok.

In our hierachy a IKGoal was created on our skeleton heel. When we selected 3 bones and assigned the IK, the last bone selected will create a locator. This locator named 'bone_L_thigh_IKGoal' will be the ankle.
Exit [Setup] .We can move this 'bone_L_thigh_IKGoal' and it will move the foot.
    When we move the leg foward our knee bends backwards. This is great if we want to animate an ostrich, however we don't want this kind of animation in a human character.
The solution is the knee should be ahead of the ankle to prevent collapsing. Now lets make the knee control and fix this knee problem.

2) Knee control

Enter [Setup] With our Dual Joint PlanarIK selected we can now click on [Create IK Up Vector] on the left panel.
    1) Rename the 'IK Up Vector' to 'controller_L_knee'. This will be our knee controll.
    2) Change the shape to a pyramid and increase its size. Now perform a [drop action: match] and drop it over the knee joint 'bone_L_knee'.
    3) Exit [Setup] and activate [Local] on the top right. This is important so the knee does not rotate or move when we position our knee control. Move the knee control foward. By moving the knee controller away from the heel it will prevent our knee from moving backwards when we move our leg.
After you position the knee [Reset > Rotation] to return the axis position. Then click [Zero > All].

3) Making the foot roll

Let's rename 'bone_L_thigh_IKGoal' to 'IK_L_ankle'. Now take a look at how the foot roll is created through the hierachy. First we have the 'controller_L_ankle' which is the box shape around the ankle. This has been positioned to match the bone 'joint_L_ankle'. This is a child of the 'base_global'.
Create 4 locators and use a [drop action: match] to position them. Rename each locator as shown in the image. I used the naming convention 'PIV' because this will be the pivot when we animate our foot roll.
Our heel pivot will be the parent. 'IK_L_ankle' will be the child at the end. Parent accordingly to the hierachy shown. Now create another locator name it 'controller_L_ankle' and [drop action: match] to 'joint_L_ankle'.

This box control will be a parent to all the locators we created earlier. Everything else will go below 'controller_L_ankle'. Finally 'base_global' will be the parent to 'controller_L_ankle'.
There's one more step! we need to add modifiers so the ankle can rotate and the rest will follow. Select 'joint_L_ankle' and ctr+select 'effector_L_foot' and add modifier [Rotation].
We can now test our foot roll system. Select the 'controller_L_ankle' and rotate and move.
When we rotate our foot we want to do it at the pivot. Offset the heel and toe pivots and give them a box shape so that we can easily select it when we need it.

4) User Channels

With user channels we can create our own slider to increase or decrease a value. This becomes useful for animation when we want a custom control such as a face rig or a foot roll. When our character walks we don't want to animate the bending of the heel and toe every step of the walking animation. By creating a custom channel we can automate this process.

Rigging can be a visual task as well as a technical one. So were going to do this in steps.

Step 1) Creating a User Channel
Select the 'controller_L_ankle'. Create a user channel and name it 'FootRoll'

Were using a [Type: Float] because this gives us decimal values. Min Value: -1 Maximum: 1 .Check the boxes. Click OK.
Right click the channel we created and choose channel links. This opens up a Channel Links window. Click [Load Driver] on the top left, this will load our custom channel into the Channel Links window on the left side. Scroll to the bottom on the left panel and you will see our custom channel 'Foot Roll'.

Load Driver is what we use to control the the animation. Load Driven is what is being affected by the driver.

Step 2) Links
Now select 'controller_L_foot' and click on [Load Driven] on the top right Channel Links window. With 'controller_L_foot' selected press 'e' and rotate the foot. I am checking the axis that makes the foot rotate foward and backward. When you rotate the 'controller_L_foot' it will highlight in the Channel Links window. These are the rotations we want to use. In this case it is the X axis that I want to use.
Select the Foot Roll on the left window and select the Rotation X on the right. Then click [Relationship] and click [Add Link]. What this does is connect the FootRoll user channel we just created to the Rotation X of the joint 'controller_L_foot'. Now when we use the FootRoll channel it will affect the 'controller_L_foot' Rotation X.

What's the difference between Direct Link and Relationship?

Direct Link will match both values meaning when we rotate the 'controller_L_ankle' it will also affect the 'controller_L_foot'. However the foot controller can only rotate until it reaches a stopping point.

Relationship will allow us to continue this rotation and gives us more felxibility. So for that reason we use Relationship.

Step 3) Channel Haul
Toggle the [Channel Haul] button or click it twice. A window will appear. Change your Driver FootRoll to 0.5. Notice that nothing has happened to our foot. That's because we need to tell MODO what to do with this foot control when it is at 0.5

To do this we use Save States. Save States are like pressing pause on a film. The saved state acts like a bookmark and you can return to that state at any time.

Now change your Driven Rotation X to 50. Our ankle will move upwards. What this will do is rotate our foot roll when we are at 0.5 on the Driver FootRoll. Anything past 0.5 and before 0.0 nothing will happen because we have not saved any states for them. Click on the yellow square to save the state and test it by dragging the small square left and right on the Driver FootRoll. Click on the red 'X' to delete states. When done return the FootRoll back to Zero. Now we can connect other controls in the Driven so we can add a different type of animation to our Driver FootRoll.

5) IK for the right leg!

Making IK for the right leg is the same process. Use what you learned and practice. Remember to use the naming convention '_R_'.