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What is a constraint and how do we use it?

From: Creating Simulations in MassFX and 3ds Max

Video: What is a constraint and how do we use it?

Whenever we add a dynamic rigid body modifier to an object or objects in our scene, they become subject to the law of gravity. This should mean of course it is enable in our global options. However having all free-floating objects in the scene automatically fall to the floor may not be the desired end result. We may, for instance, find ourselves needing to fix certain objects in places, it were, locking them to a specific point in 3D space. Alternatively, we may need to create complex relationships between two objects in the scene, such as having them dynamically slide against one another within a fixed set of boundaries or revolve around one another on a fixed axis.

What is a constraint and how do we use it?

Whenever we add a dynamic rigid body modifier to an object or objects in our scene, they become subject to the law of gravity. This should mean of course it is enable in our global options. However having all free-floating objects in the scene automatically fall to the floor may not be the desired end result. We may, for instance, find ourselves needing to fix certain objects in places, it were, locking them to a specific point in 3D space. Alternatively, we may need to create complex relationships between two objects in the scene, such as having them dynamically slide against one another within a fixed set of boundaries or revolve around one another on a fixed axis.

In these and other such situations, we will want to make use of a set of tools called constraints. As you can probably surmise from the name, a constraint inside a dynamic simulation restricts the movement of particular objects that are part of the rigid body simulation. The idea of a constraint is that it creates hierarchical parent-child relationship between two entities. Some examples of constraints in the real world would include hinges, nails, curtain rails, and axles, to name just a few.

Now in MassFX in 3ds Max, all of the constraint types that we will mention here are available as preset options, although it is probably worth noting that they're all just variations of the universal constraint but that have particular settings already applied to them. Of course, all good dynamic simulation tools will have these or similar constraint options available. The simplest constraint type we can use in a rigid body simulation is often referred to as a rigid or fixed constraint, and really, its name tells us exactly what it is designed to do.

By default, a rigid constraint will have all of its transform options locked. This means there can be no movement, rotation, or twist action at all once a simulation starts. It really does lock an object in position. It can also be used to lock two objects together so that they move and behave as one inside the simulation. Another typical constraint type we may come across could be the Slide constraint--very similar in construct to a rigid constraint, except in this case we do have a limited single-axis translation enabled.

In MassFX this is the Y axis by default, but of course this can be altered. We might also find we have a Hinge constraint available. This usually has a single swing axis enabled that has a limited swing range set in degrees. We might also find a twist constraint, which will probably have a single axis twist value that has been set to unlimited or unconstraint. This would allow an object to twist, or as I prefer to think of it, spin freely. In MassFX we also get two other preset constraint types that we can work with, these being the universal constraint that has two swing axes set to a limited value, such as 45 degrees, and a ball-and-socket constraint that uses two separate swing axes limited this time to 80 degrees, but also with a twist amount set to unlimited.

In a rigid body simulation any objects that have been set as dynamic rigid bodies will be subject to the laws of gravity, motion, and collision, meaning they will start to react in a fairly random manner as soon as a simulation is enabled-- unless, that is, we introduce constraints into the mix. With our constraint tools, we can start to craft very specific behaviors from dynamic objects, creating complex motions and interactions that would be otherwise impossible to achieve.

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This video is part of

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Creating Simulations in MassFX and 3ds Max

51 video lessons · 2431 viewers

Brian Bradley
Author

 
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  1. 3m 27s
    1. Welcome
      58s
    2. Working with the exercise files
      46s
    3. Setting up the 3ds Max project structure
      1m 43s
  2. 39m 20s
    1. Why simulate and not animate?
      3m 38s
    2. A look at gravity and drag
      3m 55s
    3. Understanding volume, mass, and density
      3m 45s
    4. What are Newton's laws of motion?
      3m 20s
    5. Finding believable frames per second and substeps
      3m 5s
    6. Understanding the difference between rigid and soft bodies
      3m 28s
    7. More about rigid body types
      3m 32s
    8. How collisions are calculated
      4m 35s
    9. Learning the difference between concave and convex meshes
      6m 24s
    10. What is a constraint and how do we use it?
      3m 38s
  3. 24m 20s
    1. A look at the MassFX and the 3ds Max user interfaces
      5m 52s
    2. Exploring the MassFX workflow
      5m 14s
    3. Discovering ground collision and gravity
      4m 49s
    4. Adjusting substeps and solver iterations
      3m 43s
    5. Using the Multi-Editor and the MassFX Visualizer
      4m 42s
  4. 44m 11s
    1. Breaking down the shot
      4m 51s
    2. Setting up the launchers
      3m 59s
    3. Setting up the drop system
      4m 30s
    4. Prepping the cans
      3m 33s
    5. Refining the simulation on the launchers
      5m 9s
    6. Refining the simulation on the colliders
      6m 5s
    7. Baking out the simulation for rendering
      5m 37s
    8. Reviewing the simulation with an animation sequence
      5m 3s
    9. Adding an animation override
      5m 24s
  5. 33m 32s
    1. Adding a rigid constraint and creating breakability
      8m 3s
    2. Creating a moving target with the Slide constraint
      4m 47s
    3. Creating springy targets with the Hinge constraint
      5m 59s
    4. Spinning targets using the Twist constraint
      4m 57s
    5. Creating crazy targets with the Ball & Socket constraint
      4m 58s
    6. Constructing a MassFX Ragdoll
      4m 48s
  6. 36m 51s
    1. Applying the mCloth modifier and pinning the hammock
      5m 55s
    2. Setting up the hammock's physical properties
      5m 39s
    3. Working with the mCloth interaction controls
      6m 14s
    4. Attaching the hammock to animated objects
      4m 5s
    5. Putting a rip in mCloth
      6m 14s
    6. Using mCloth to create a rope object
      4m 53s
    7. Creating a soft body object
      3m 51s
  7. 14m 47s
    1. Adding forces to a simulation
      5m 27s
    2. Putting forces to practical use
      5m 33s
    3. Using forces with mCloth
      3m 47s
  8. 35m 27s
    1. Walking through mParticles
      4m 38s
    2. Using fracture geometry
      6m 0s
    3. Creating breakable glue: Part 1
      4m 19s
    4. Creating breakable glue: Part 2
      5m 19s
    5. Creating a gloopy fluid: Part 1
      4m 14s
    6. Creating a gloopy fluid: Part 2
      4m 41s
    7. Adding forces to mParticles
      6m 16s
  9. 1m 5s
    1. What's next?
      1m 5s

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