Manual Modules MOCCA Soft IK / Bones MOCCA IK Tag
MOCCA IK Tag Basic Tag Constraint Limit RestConstraint
Constraint
This page is shown only if Anchor is disabled on the Tag Properties page.
The Constraint settings define the controls that force the IK chain into another form or direction; they allow another object to be used to move the bone chain.
Here’s a more precise explanation: the goal constraint uses the origin of virtually any object in the scene to enable you to force the IK chain towards the position of that object, assuming that the other potential constraints in your scene do not counteract this. Since the IK chains follow the goal constraints, the bone angles will also be modified. Therefore this is useful for setting up different poses, since all you have to do is move about individual goal constraint objects.
If you want the chain to point at a constraint, you will have to work with a tip effector. In other words, a null will be placed at the end of a chain and linked to a goal constraint. This works similarly when you use the Set Up IK Chain command.
Drag an object from the Object manager into this box. This object will then serve as a goal constraint. You can remove an object from this box by clicking the small triangle next to it and choosing Clear from the drop‑down list that appears.
These buttons allow you to add a root goal or up vector.
Imagine setting the ‘muscular’ force at which the constraint pulls on the bone. If you have used several constraints with different strengths in your scene, the ones with the higher values will be preferred by the chain.
You can very easily obtain control over unwanted bone rotation using the option Use As Pole.
Pole vectors represent the planar surface between these three points.
Pole vectors represent a planar surface between the following three points (see image) of a pair of bones:
- The beginning of the first bone.
- The end of the first and beginning of the second bone.
- Around the end of the second bone.
The result is that the bones cannot be rotated independently of each other; the rotation of the two bones is now controlled by the pole vector.
Use As Pole only has an effect when used with a root goal; the option has no effect when used with a tip goal. This is down to the way that goals are created — root goals are attached directly to the bone they should affect, whereas tip goals are assigned an extra Null object.
The behavior of the Distance setting depends on the Chop Sticks setting. If Chop Sticks is enabled, this parameter sets the length of the chopsticks (see below). If Chop Sticks is disabled, it defines the distance between the tip effector and tip goal constraint within the bone chain.
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| Chopsticks enable you to rotate the chain around the value of the Distance setting. |
This setting, when enabled, allows you to move your character as if the joints were connected to sticks, like shadow puppets. When using chopsticks you can pivot around a point connected to an arm
just like the wheels of a locomotive train. Set the length of the chopsticks using Distance (see above).
This button is only available when Use IK option (on the Tag Properties tab) is disabled. When using chopsticks the Distance parameter allows you to change the distance from the control object to the bone. To do this, switch off the MOCCA IK, move the control object to the desired position, click Set and switch the MOCCA IK back on. The new value for the distance will appear in the Distance box automatically.
Up Vector
There are cases in which the chain may have various alternative ways of conforming to all the constraints. Take a leg, consisting of an upper and lower thigh. The upper thigh is parented to a root bone and the lower thigh has a tip effector, which is linked to a goal constraint. If you move the goal constraint, the chain has no clear way of knowing how the angles behave between root and effector. On longer chains this can sometimes cause chaotic twisting of the IK chain. Obviously you’ll quickly notice this when the character’s skin is fixed to the bones, as it will twist with the chain. The Up Vector gives you a chance to prevent this from happening by constraining the orientation of the bone axis to the Up Vector constraint.
Here you can drag and drop an object from the Object manager. That object will then be used as an Up Vector object. Delete the Up Vector by clicking on the small triangle next to it and selecting Clear.
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| Up Vector constraints let you orientate the axis of a bone towards a control object. In this case, not the position, but the angle of the bone will be modified. |
This value defines the strength at which the fixed axis will be pulled towards the Up Vector constraint. A value of 0% will completely ignore the constraint. A value of 100% practically nails the axis to the constraint. A value of 50% orientates the bone with a bit of lag, just like a magnetic compass needle adjusting towards true North after the compass has been moved.
Here you can choose between the various axes that point towards the Up Vector. The options are Y, -Y and X, -X. If you choose -Y, the Y‑axis will point in the exactly opposite direction of the Up Vector, since an object axis arrow always points positively.