Setting Up a Hierarchy

Hierarchy for objects/geometries needs to be set up before you begin any animation that has multiple parts. As an example, load Hierarchy_Start.max from the source files folder. A simple robotic arm has been created with basic primitive shapes (probably not the best modeling you have seen, but this should suffice for now). See Figure 3-1. At this point, see if you can move the robotic arm from its default pose to a different pose.

If you try to pose the arm in a different way, you will notice that the arm is made of multiple parts. That means that posing it is tedious. Now go ahead and swivel the arm 360 degrees on its base or have the claw pick up and play the animation. This is tough and you might end with animations where the parts move away from each other. The purpose of this section is to show how to address these problems.

Reset your workspace by selecting standard design so that the Scene Explorer is docked on the left view. Alternatively, you can open Scene Explorer by choosing Tools menu ➤ All Global Explorers ➤ Scene Explorer. (Refer to Figure 3-2.)

Once you open the Scene Explorer, you should see the Scene Explorer panel with the hierarchy of the robotic arm, as shown in Figure 3-3.

Once the Scene Explorer is open, you can see that there are many primitive shapes that make up the robotic arm. As you can see, my naming conventions for mesh are nonexistent and this is for a reason. To rename the primitives, select one in the Scene Explorer, right-click, and choose the Rename option. Once you have given it an appropriate name, save it and proceed.

If you look before each primitive name, there is an eye icon that toggles the visibility of the object and a snowflake icon on the right, which freezes the mesh but leaves visibility so that you don’t accidently select it in the viewport. As you can see, except for the segment in pink, every other primitive is frozen and the claws are set to invisible (note the eye icon).

The leftmost column shows the switches used to toggle the visibility of objects based on type (see Figure 3-4).

Once you have renamed the files the way you want, you need to set up a hierarchy so that rotating sphere001 reorients all the others as well. Hierarchy can be set by dragging objects and dropping them below the one you want them to be a child of. In essence, the topmost object is the parent and the ones under it are the children.

Load Hierarchy_Structured.max and see what I have set up. Note that box002 and box003 are children of box001. Use the Rotate tool from the toolbar or press E shortcut for rotate and try rotating any joints. You should see that the children follow their parent’s rotation. By dragging and dropping items in the Scene Explorer, we have set up hierarchy so that animating this hand is a lot easier. We should be able to pose and animate the robotic arm in a much easier way. See Figure 3-5.

Go ahead and animate the hand by trying to pick an imaginary object. You will notice that the claws won’t rotate to give the crab-claw kind of motion.

Objects rotate around their pivot and a pivot by default is located at the center of the mass of an object, but this can be relocated as needed. Spheres have the pivot in the center by default, as they are symmetrical on all axes. The box in its current state cannot be animated like a claw hand since it needs to have the pivot at the base for it to have a claw motion. How do we fix this?

Setting Up a Pivot

When you select the claws that make up box002 or box003, you’ll notice that the pivots are in the center. We need to change them to the base so that the clawing motion can be achieved.

Notice the claw and the rotation pivot in the middle. Open the hierarchy panel open by clicking on the Hierarchy tab from the control panel. See Figure 3-6.

Clicking on the Hierarchy tab from the command panel will populate the tab with hierarchy data and give us options to tweak to our liking. See Figure 3-7.

Once you have selected the object box002 and have the Hierarchy panel open, choose Affect Pivots Only from the Hierarchy tab (see Figure 3-8). You will be able to reposition the pivot to the desired location.

In this case, I recommend you go to the top viewport and orient it, as shown in Figure 3-9, for both claws.

Once the pivots are set, click on the Affect Pivot Only button to exit pivot editing mode and rotate the claws. Voila! The animation works correctly. Load the Hierarchy_StructuredwithPivots.max file. Animate and experiment.

Attachment Constraint

If we are not using the constraint, we would animate the ball to match the movement of the arm, but if someone were to change the arm’s animation path, the ball would need tweaking as well. The Attachment constraint comes to our rescue here.

Let’s have the robotic arm pick up the ball and place it on the table.

1. 1.

   Select the ball that needs to move with the arm and choose Constraints and Attachment constraint from the Animation menu. Your cursor will change to a ribbon dotted line. The software waits for you tell it what object it is attached to, with the ribbon line clicked on the helper box that we created. See Figure 3-11.

    
2. 2.
   Once you choose the Attachment constraint, the ball moves to the helper object and sticks there. This is not what we want. We want the ball to be picked up and placed. We need one more step to achieve that effect.

   

   With the ball still selected, go to the motion panel in the control panel. See Figure 3-12.

   

    
3. 3.

   Select the Attachment constraint in the position list pane of the motion panel and animate the weight so that it is 0 from frames 0 to 29 and set to 100 at frame 30. Weight can be locked by turning on the auto key and changing the value to 0 at frame 0. At frame 29, change the value to 1 and 0 back again so that a key is created. At frame 30, change the weight value to 100.

    
4. 4.
   You might notice the ball moving from frame 0 to frame 29 in an unexpected way, as seen in the checkpoint file called RoboticArm_Attachment_Constraint_Curve.max. Open the Curve Editor and set both keys to linear for the weight for frame 0 and 29 and that should fix it. See Figure 3-13.

   

    
5. 5.

   Tweak the graph as shown in Figure 3-14 by setting the keys 0 and 29 to linear. Then play the animation.

    

Taking this a step ahead, if you want the robotic arm to place the ball on the box named table, you need to add another Attachment constraint to the sphere and choose the table. Animate the weight to 100 only when the ball needs to be kept on the table. The same technique can be applied to character animation, when a character has to pick up and place something.

Surface Constraint

The Surface constraint is used when you want to conform an object to stick to the surface of another object. This constraint works only for parametric objects, thus limiting the scope of how we can use them freely.

Here’s a simple example to show you how it works. Load surfaceconstraints.max.

1. 1.

   Select the cylinder and choose Animation ➤ Constraints ➤ Surface Constraints and then select the sphere.

    
2. 2.

   In the motion panel, go below to the surface controller parameter and use the U and V sliders to manipulate the cylinder on the sphere geometry. See Figure 3-15.

    

Reference the SurfaceConstraintComplete.max file, which has been provided in the source folder.

Path Constraint

The Path constraint is used when you want an object to follow along a specific path. It not only allows the object to follow the path, but also orients and tilts it according to the change in the path’s direction. A typical example is to have a skater move along the path and then later manually animate his hands for balance based on twist and turns.

Another typical example is to animate a bird flapping its wings endlessly and then put it on a path to fly.

Position Constraint

When you apply the Position constraint for object A to object B, the position of A is locked to B. That means you can no longer change the position of A manually. If you move object B, object A will move along.

Load the positionconstraint.max file:

1. 1.

   If you notice, we have three objects in the scene: two boxes and a sphere.

    
2. 2.

   Select the sphere and choose Animation ➤ Constraint ➤ Position Constraint.

    
3. 3.

   With the wiring enabled, select one of the cubes.

    
4. 4.

   Your sphere now immediately moves to the cube’s location.

    
5. 5.

   Go into the sphere’s motion panel and choose Keep Initial Offset. This keeps the sphere where it is.

    
6. 6.

   Now try moving the sphere using the Move tool. It is locked in position, as it is deriving its position from another object.

    
7. 7.

   Select the sphere again and choose the Position constraint. Choose the other cube. When you have more than one position controller applied, you can control the weight. Play around with the values to see how we can influence the sphere’s position by moving the two cube geometries in the scene.

    
8. 8.

   Note that the sphere can be rotated and scaled regardless of the position of the cubes. See Figure 3-17.

    

Reference file Positionconstarint_Complete.max is available in the source files folder.

Link Constraint

The Link constraint allows you to dynamically change the parent as and when needed. The Link constraint works like the Attachment constraint, but with the addition of having the parent/child relationship animated, which is not available otherwise.

If you look back at the previous section where we discussed the Attachment constraint, we had the robot pick up the ball and move it. If we were to have another robot receive the ball, we would need the Link constraint. The Link constraint lets you animate the link.

Load LinkConstraint_Start.max and play the animation to see what we have. Notice we have two boxes and a sphere, and everything is animated.

I want you to pay attention to the way they are positioned. Note at frame 15 that box001 and the sphere come into contact and the ball and sphere move in their animated direction. At frame 24, we have both boxes converging and moving on after that frame.

We used the Link constraint to create a dynamic parent for the sphere at various points of time. This was not possible otherwise. A checkpoint reference file is created for you to preview called LinkConstraint_Completed.max.

LookAt Constraint

The LookAt constraint creates quick and efficient eye rigs for characters. The object is oriented along the axis of the target. This is done by locking an axis to always face the target.

This technique can be used for anything that needs to track another object, such as a surface to air missile launcher tracking a fighter jet in the air, or a predator keeping its prey in sight. A checkpoint file called Lookatconstraint_Finish.max has been created for you to see the final result.

Orientation Constraint

The Orientation constraint is similar to the Position constraint. The difference is that the Orientation constraint will lock the rotation of the object, although the object can be scaled or repositioned. Having multiple Orientation constraints allows for average rotations applied based on the weight of each target.

A typical use case for this constraint would be for window blinds. Instead of manually animating each blind, a single main object can be animated and other pieces that make the windows blind can replicate the rotation.

We used the Orientation control to rotate the window blinds. This will save a lot of time, when you don’t want to select each one and rotate. Position and scale are not locked in this constraint, so you are free to manipulate them. (The OrientationConstraint_finish.max file has been added for your reference.)

We will use all these constraints to develop character animation in the upcoming chapters. In the next chapter, we look at wire parameters and advanced controllers.