Using Hinge Constraints

Rag Doll Tutorial

Using Rag Doll Constraints

 

Autodesk 3ds Max Tutorials > Special Effects > Rag Doll Tutorial > 

Setting Up Knees, Elbows, Ankles and Wrists

Open the sample file:

• You can continue from where you left off, or choose File menu > Open and load the character01.max from the \tutorials\reactor\ragdoll directory.

Using a constraint is similar to the Rigid Body Collection, but this time you add a Constraint Solver to the scene. Next you can begin to add various constraint types to your objects and then add them to this solver. The solver, in essence, figures out how best to keep all of your objects happy under the conditions they've been given (body A connected to body B, body B connected to body C, etc.).

Add a Constraint Solver to the scene:

1. On the Create panel, click Helpers and choose reactor from the drop-down list.
2. On the Create panel > Object Type rollout, click CSolver.
3. Click in one of the viewports to create a Constraint Solver.
   NoteThe location of the helper object is not important.

   

   NoteThe Constraint Solver works only if all the constraints act upon rigid bodies that belong to the same Rigid Body Collection.

   Next, you'll specify the collection to which to apply the Constraint Solver.

4. With the solver selected, open the Modify panel > Properties rollout, and click the button labeled None, below RB Collection.
5. Press H and choose RBCollection01 from the Pick Object dialog.

Now you're ready to start connecting bones together, and soon will have your rag doll tumbling down the stairs. You'll use the Hinge constraint to connect the various bones in the character, first joining the right foot and calf bones to simulate an ankle.

Create Hinge constraints for the ankles:

1. On the Create panel > Object Type rollout, click Hinge.
2. Click anywhere in a viewport to create a Hinge constraint.

   

   Next you'll choose the objects to which to assign to this constraint.

3. In the Modify panel > Properties rollout, click the button labeled None, next to Child.
4. Press H and choose RFoot in the Pick Object dialog, then click Pick

   The Child button should now read RFoot.

5. On the Modify panel > Properties rollout, turn on the Parent check box.

   This indicates that you want to constrain two objects together, rather than one object to the world.

6. Click the button labeled None, next to Parent.
7. Press H, choose RCalf from the Pick Objects dialog, and then click Pick

   The button beside Parent should now read RCalf and the scene should look like this:

   

   In its current state, the character's foot is free to rotate 360 degrees around the hinge constraint, which as you can imagine would be pretty painful! You need to use the Limited property for this hinge constraint.

8. On the Properties rollout, turn on Limited.
9. In the Limited group, set Min Angle to -20.0 and Max Angle to 30.0
10. Repeat this process for the left foot and calf bones.

    

Create Hinge constraints for the knees, elbows and wrists:

• The process for setting up the hinge constraint for each of the other bone pairs is identical, with only the constraint limits differing. With this in mind use this list to set the constraint parameters for each joint:

  Constraint Name	Child	Parent	Min Angle	Max Angle
  RAnkleJoint	RFoot	RCalf	-20.0	30.0
  LAnkleJoint	LFoot	LCalf	-20.0	30.0
  RKneeJoint	RCalf	RThigh	-85.0	0.0
  LKneeJoint	LCalf	LThigh	-85.0	0.0
  RWristJoint	RHand	RForeArm	-35.0	35.0
  LWristJoint	LHand	LForeArm	-35.0	35.0
  RElbowJoint	RForeArm	RUpperArm	-85.0	0.0
  LElbowJoint	LForeArm	LUpperArm	-85.0	0.0

  When you're done, the scene should look like this:

  

You'll simulate the other bones using Rag Doll Constraints, as their motion is more sophisticated. The last thing you have to do is to add all of the constraints to the Constraint Solver.

Add the Hinge constraints to the Constraint Solver:

1. Press H, and on the Object Select dialog, choose CSolver01 and click Select.
2. On the Modify panel > Properties rollout, click Add.
3. On the dialog, highlight all of the hinges and click Select

   The CSolver Properties rollout should now look like this:

   

Next you'll preview the scene again to see just how these alterations have affected the character.

• On the Utility panel, click reactor, and then on the Preview & Animation rollout, click the Preview in Window.

You might have noticed during the last preview that reactor complained that some of the rigid bodies in the scene were interpenetrating. Although you ignored this warning on that occasion, it's not a good idea to do in general. Later in this tutorial, you will take care of this issue, but for now click Continue and view the preview.

The first thing that stands out is that the bones connected with hinge constraints stay together. This is exactly as planned, but notice that they continue bouncing and dancing about once they hit the floor. This is because reactor notices that the bones are interpenetrating with one another and tries to separate them. However, at the same time, the Constraint Solver is trying to keep them together. Since they are essentially battling with one another over the position of the various bones they continue to bounce about erratically. The solution to this is to tell reactor not to worry about interpenetrations between the bones that you've connected.

Disable collisions between the limbs:

1. On the Utility panel > reactor > Collisions rollout > Global Collisions group, click Define Collision Pairs.

   

   You are presented with the following dialog:

   

   There are three columns: one for all the entities (objects) in the scene, one for enabled collisions, and one for disabled collisions. By default, all collisions are enabled between all objects so you need to tell reactor to ignore the collisions between the bones in your character. You want to ignore only bone-to-bone collisions, though. If, for example, you chose to ignore the collision between the character's foot bone and the floor object, the character's foot would pass straight through the floor unimpeded.

2. Select all of (and only) the bone objects in the first column.

   This displays a list of enabled collisions in the second column.

3. Click the >> button

   

   All of the collision pairs between the selected bodies move to the third column (disabled collision pairs).

4. Click OK to accept the changes.
   NoteInstead of disabling all collisions between all limbs, you could instead disable collisions between adjoining limbs. In order to do so, you would start with all collisions enabled, select each adjoining pair ( LHand and LForeArm , Spine3 and Head , etc.) and click ">>" to disable just those pairs.

Preview the animation with collisions disabled:

1. On the Utilities panel > reactor > Preview & Animation rollout, click Preview in Window.

   The Preview window should open this time without any warnings and everything should behave as expected (no bouncing limbs).

2. Save your work again, this time as my_character02.max