Ikas Blender 3D ( 4 - Constraints )

Introduction - Armature and Mesh - First animation - A little more - Weight - Weight paint -Various Tricks

Constraints:
Combined with the armature system, constraints offer an almost unlimited range of possibilities for animation. Moreover, constraints can also be applied to all of the types of objects available in Blender. There are 4 types of constraints:
'Track to', 'IK Solver', 'Copy Rotation' and 'Copy Location'.
To apply a constraint: Select an object and press the 'chain' icon button in the menu header bar and then press Add to obtain this:
The small white dash '-' button besides 'Track To' allows you to select one of the four types of constraints. You can rename the constraint ( 'Const' by default ) and the 'OB:' box in which you enter the name of the object that you have selected, which you wish to have the constraint exerted upon. Recall: The name must be entered exactly with respect to upper/lower case letters, if it is not, the contents of the dialog box will be erased. If the title bar changes to red - attention! You have made an error and in matters concerning constraints, when Blender is not content, Blender crashes! ( V2.20 ).
The .blend example files for this page, can be opened from the various links located throughout the page.

1/ Track To: If you have already used the CTRL +T ( Make track ) option, then you should not find this feature too confusing. The selected object will have one of its axes permanently oriented towards the indicated object. The most typical example applies to the camera. To obtain the result shown below, all you need to do is select the camera and enter the name of the target object into the constraints dialog box.
Note: The target object ( Empty ) does not have to be selected, it appears pink here, only so that it is more visible in the image.
The Animation buttons window ( F7 ) shown partially visible in the image below with a portion of it hi-lited in red, does not really form part of the new options, but it is probably a good idea to recall that the object subjected to a constraint will perhaps not take the desired orientation with your first try. Therefore, it will be necessary to use this window to select the axis which must undergo the constraint. In the case of tracking, the first 3 buttons in the group of 6 determine which axis is orientated towards the target, the following 3 buttons, in the same group, will orient the opposite axis towards the target by performing an 180° rotation. The seperate group of 3 buttons ( 'Up' ) indicate which of the remaining two free axes will be orientated upwards.
The example is rather banal, but it best illustrates a means with which to aim a camera. ( ex-01.blend )

A little more convincing example: Once again, use the armature previously created and apply the two positions shown below to it, for frames 1 and 50 ( as explained in the previous pages ) and then play the animation. Next, add an 'Empty'. Select 'Bone' B3 in 'pose' mode ( Blue ) and create a 'Track to' constraint for the Empty before playing the animation.
This introduces some interesting possibilities. Each 'bone' can be subjected to a particular constraint, each 'constrained' object modifies the shape of the armature if it is moved. If, in this example, it is a simple empty object which is used as a constraint, it could also be a moving element. As if that was not enough to create very complex movements, the same object can be subjected to several different constraints produced by various objects.
Do not forget to play a little with the x ,y ,z buttons in the Animation buttons window to see the results. ( ex-02.blend ).

2/ IK Solver: This constraint generally relates to the origin ( the thickest part or root ) of a 'Bone'. Either in the same armature or in another. When this constraint is defined, initially it is necessary to provide the name of the armature which transmits it and then the name of the source 'bone'. Once this is done, the source 'Bone' will attract the 'bone' subjected to the constraint towards its root/base. The file ( ex-03.blend ) displays, at the top, a static armature ( which does not have any animation key ). Its last element ( Bone.004 ) is subjected to an IK Solver due to bone B3 of the second armature which is animated. When you launch the animation, you will notice a "magnetized" effect produced by the movement of the second armature.

In the IK Solver dialog box, increasing the tolerance, increases a little the radius anchoring (clearance distance) between the two 'bones'. Iterations determines the action (operating) radius and the intensity of the magnetism. Increase this value if the "connection" is not made fairly quickly or decrease it if the animation is sluggish. ( Default Value = 500 ). A classic method consists in using this form of constraint to add bones acting as 'handles' to manage the global animation of an armature. It is this process which made it possible to manage Ikas in the previous versions of Blender.
3/ Copy Rotation: Here, a small adjustment to the Edit buttons window (F9) is essential ( With the armature selected ) click on the 'Draw Axes' button. With this done, pivot the empty so as to align its axes as compared to that of the armature. The 'Animation buttons window' (F7) will not be able to do anything here for you, if the constrained object takes an unforeseen orientation. Once the constraint has been carried out, the selected object will always remain parallel to that which imposed the constraint. It is obvious that if this last one is animated by a rotation it will be transmitted to the constrained object during the animation.
3/ Copy Location: This constraint allows you to lock the position of the constrained object relative to the object named in the 'Target Object' (OB:) constraints box. You can choose the axes on which the object will be locked. The ex-04.blend file contains a small animation using these types of constraints.