The zip file consists of the initial scene, the completed scene with HyperMatter for reference if you get stuck, and some image files that must be placed in 3DSMAX2/Maps.

NOTE: The scene file is saved for use in MAX2. It will not work if loaded into MAX1.2

Load scene file Mousetrap1.max

Understanding the problem

The scene consists of a mousetrap object and assorted components in position, and a pre-sliced mouse also ready. All the components of the scene except the ‘Victor Wood Base' object are already linked to an invisible object ‘Base box’.
The mousetrap simply falls to the floor during the course of the animation, which sounds simple enough; however, the nature of the scene presents us with some unusual problems that must be overcome.

Firstly, the mousetrap components must behave rigidly, but still move independently of the mousetrap base. For example, the trap rod must be free to swing around, but still remain physically attached to the hook.
Secondly, we are faced with the logic problem of HyperMatter solids or parts of solids not being allowed to Follow other HM objects; this severely impedes the functioning of the mousetrap as we envisioned it, as ALL the parts of the mousetrap must follow the base exactly.

The only way around this, and similarly in other linkage-type scenes, is to build the HyperMatter animation in different stages. We know that ultimately the base of the mousetrap is the ‘master’ object in the scene; all other objects initially depend on this object for their overall position and orientation.
Therefore, we can confidently run the animation with ONLY the base of the mousetrap solidified. This will give us exactly the bounce we need, with minimum time penalty.

This also allows us to take advantage of the Record object facility within HyperMatter. Record objects are standard MAX morph targets that HyperMatter can generate from its solid objects on the fly. Once generated, the Record objects can be manipulated in real time as any other MAX object, whilst still retaining the original HyperMatter dynamic information.

NOTE: It is critical in this animation that once the Record object is generated, you do not change the orientation of any of the objects, as they all depend on the Record object’s orientation to work correctly.

Animating the Base - Record Objects

We will generate the Record object to replicate the bouncing of the base, and then link all the other components to that.

1. Select geometry object Victor Wood Base, and convert it to a HyperMatter solid, choosing a resolution of 1 and a fit along the X axis.

2. Go to the Substance editor, and access the ‘Use Library’ rollup. Select ‘Wood’ from the presets menu.
The Dimension value for this object should be 20.152 for the correct behaviour…you may get a slight variation of this when you solidify the object, so change it to the value above.

3. Go to the Constraints editor. Select the preset part ‘All’ from the selection sets field, and apply a Velocity Constraint and a Set constraint to the part.

4. Leave the Set constraint to its default lifespan, and set the Velocity constraint to run from frames 0 to 10, choosing Whole Part as the constraint option. Click in the Y checkbox, and enter a value of 50.

Now run the animation and check that the box bounces correctly on the table.

Save the scene as Mousetrap02.max

We have the HyperMatter base behaving as we wanted; now it’s time to generate the Record object.

5. Leave Sub-object mode if you are currently there, and with the base solid selected, click ‘Record’ in the Create panel.

6. Now select the Record object R_Victor Wood Base and go to the Modify panel.
Select ‘Auto-create Keys’, and when prompted, select a range of frames 0-300, and a frame interval of 10. Hit OK, and HyperMatter will generate the morph targets automatically.
We do not need to generate any further keys, as the base has completely come to rest by frame 300.

Once the operation is complete, you can choose either to hide or delete the HyperMatter solid, as we will not be using it any further.

Save the scene as Mousetrap03.max

Linking HyperMatter Solids to Record Objects

Now we are going to apply HyperMatter to some of the other objects in the scene. First, select the object ‘Base box’, which is simply a dummy object with a transparent material applied. This is used as a reference object for linking all the components of the mousetrap together.
‘Linking’ HyperMatter objects directly to Record objects with Follow constraints can also produce unpredictable effects, so we will use the ‘Base box’ object as an intermediate step in this case to ensure fidelity. We need to link this to the Record object base so that it duplicates exactly its position and orientation.

7. Select Base box, link it to the object R_Victor Wood Base, and play the animation again.

Now all the components of the mousetrap follow the base, and duplicate its bouncing.

8. Select the mouse object, and solidify it at a resolution of 2, and a fit along X.

9. Set the Dimension value to 12.961 and choose ‘Hard Ball’ from the library of presets substances.

10. Now go to the constraints editor, and select the mesh points enclosing the base of the mouse (see picture).

11. Name the part ‘base’ or similar, and apply a default Follow constraint to it, from frames 30-950, picking the ‘Base box’ object as the follow object.

12. Now go to the Track View and set the lifespan of the mouse to begin at Frame 30.

NOTE: As we have keyframed the initial rotation of the trap rod from 0-40, we do not need the object active until this point; in fact, all the HyperMatter objects should be set to have a lifespan beginning at frame 30 to speed things up a little.

Run the animation again, and the mouse will stay with the base, responding to the keyframe animation and deforming upon collision with the HyperMatter walls (hidden).

Save the scene as Mousetrap04.max

13. Now select the object Coil Box, and solidify it at resolution 3, X fit.
This is another transparent object that we will substitute for the wire coil at the HyperMatter level to save on calculation, as it will be involved in collisions with the trap rod.

14. Go to the Constraints editor, and apply three constraints to the preset part ‘All’, Set, Follow and Collide.

15. Select the object ‘Victor Wire Coil’ as the follow object, from frames 30-950. Set the collide constraint to begin at frame 45.

16. Set the dimension value in the Substance editor to 10.651. Set the lifespan to begin at frame 30.

Using Follow Constraints for Advanced Control

The next part of the animation is a little trickier to understand. The trap rod has been rotationally keyframed from frames 0-40 to initiate its downward bouncing. We want the rod to hit the Coil box, and rattle up and down until it comes to rest. We also need the rod to freely rotate around its support hook, but not roll over sideways.

A standard Follow constraint is used initially to keep the rod aligned.

17. Select the trap rod, and solidify it using the MAX option button at a resolution of 24.

18. Now go to the Substance editor and set the Dimension value to 7.105, Damping to 1.5, Incompress to 2.0 and Friction to 0.5. Leave the other components as the defaults.
Change the sampling option from Automatic to Manual, and leave at 1.

19. Go the Constraints editor and select the preset part ‘All’. Apply a Set constraint to this part from frames 30-950. This ensures that the rod stays rigid throughout the animation. Now select HyperMatter mesh points around the trap rod pivot point (see picture).

20. Name the part and apply a Follow constraint to it from frames 30-950, and choose Whole Part as the follow option.

21. Select Victor Hoop 3 as the follow object. This will allow the rod to freely rotate around its pivot whilst still ultimately following the base.

22. Apply a Collide constraint to the Exterior of the trap rod, beginning again at frame 45. Set the lifespan of the trap rod to begin at frame 30.

To make the animation play quicker, only select a subset of the part Exterior around the point of collision (see picture), as calculations are wasted if points not actually colliding are included.

NOTE: Make sure that the two Collide constraints we have applied, to the trap rod and the coil box, are in the same collision domain, otherwise the constraints will have no effect.

Save the scene as Mousetrap05.max

Now play the animation again, and observe the behaviour of the trap rod.

Varying Follow Options and Ordering Issues

The trap rod now collides correctly with the coil box as the mousetrap bounces around; however, as the animation plays, the trap rod gradually begins to roll over on its side, reducing the realism of the linkage we have created.
To prevent the trap rod from rolling over, whilst still rotating freely around the wire hoop, we need to apply ANOTHER Follow constraint to it.
This time select the area of HM mesh completely enclosing the loop of the trap rod (see picture) and name the part.

23. Apply another Follow constraint to this part. To prevent the rod from rolling, we need to constrain it only along its X axis.

24. Uncheck the Y and Z components of the Follow constraint, making sure that the follow option is set to Each Point. This ensures that the constraint only affects the solid along its X axis of rotation, whilst still allowing it to rotate freely under the conditions of the previous Follow constraint.

NOTE: The ordering of constraints at this point is crucial. The new Follow constraint must be moved one place up the list, above the Collide constraint. This ensures that the two Follow constraints are evaluated one after another, reducing the likelihood of unpredictability caused by the collision of the trap rod.
The two Follow constraints could be usefully considered to be one ‘expanded’ constraint in this context; this is a very useful way of adding more sophisticated controls over dynamic situations.

Save the scene as Mousetrap06.max

Play the animation again, and the trap rod should correctly bounce up and down against the coil box until the mousetrap eventually comes to rest.

You could separate each collision into a unique collision domain; this will speed the whole process up, as HyperMatter will only calculate for collisions when they are actually happening. If you are using a fairly quick machine however, it is probably unimportant for an animation of this type.