Physics bodies

In Unreal Engine, physics are not an intrinsic part of a 3D mesh. A proxy shape is used for performing physics simulations. Physic bodies are simplified 3d meshes for this purpose. They come in the shape of boxes, spheres, capsules and convex hulls.

Understanding the Physics section of Static Mesh Details

Simulate Physics – When true, the body will use physics. If false, the body will move exactly where it is directed.

Mass in KG – Mass of body

Angular Damping – ‘Drag’ force added to reduce angular movement; resistance when collision happens at an angle; Controls how much resistance to rotating

Linear Damping – ‘Drag’ force added to reduce linear movement; resistance when it skims along the body; controls how much resistance to translation

Enable Gravity – If object should have the force of gravity applied.

Constraints section

Constraints: Lock Position – Translations will be limited to X, Y or Z axis

Constraints: Lock Rotation – Rotations will be limited around X, Y, and Z axis

Constraints: Mode – Lock movement along specified axis

Advanced Section

Auto Weld – Set this to true if you want the parent to absorb this body as part of a single rigid body. Root parent will dictate collision profile and body settings.

Start Awake – True if this physics body is in motion at start. False if it’s dormant.

Center of Mass Offset – Specify an origin point for the center of mass to be calculated; Useful if you want to have a lob-sided motion because weight is on extremetiy instead of center interior

Mass Scale – Per-isntance scaling of mass…. what?

Max Angular Velocity – what?

Use Async Scene – When true, it will put this body into asyncronous physics scene. False will put it in syncronous scene. If body is static, it will be placed in both….. what are these scenes they are talking about? Will not flagging it introduced frame drops?

Override Max Depenetration Velocity – what?

Max Depentration Velocity – “The maximum velocity used to depenetrate this object”…. what!?

Walkable Slope – You can define an angle that will prevent the body from proceeding to move forward in an area where the slope exceeds the defined angle. For example, if you want to define an area where a player is not allowed to walk on the grass, you can enclose the grass with a 45 degree bevel. Set the walkable slope angle to 45 degrees to prevent physics from calculating entering this restricted area.

Override Walkable Slope on Instance – “Whether this instance of the object has its own custom walkable slope override setting.”

Walkable Slope Override – “Custom walkable slope setting for this body. See the Walkable Slope documentation for usage information.”

Sleep Family – “The set of values used in considering when put this body to sleep.”

Position Solver Iteration Count – “This physics body’s solver iteration count for position. Increasing this will be more CPU intensive, but better stabilized.”

Velocity Solver Iteration Count – “This physics body’s solver iteration count for velocity. Increasing this will be more CPU intensive, but better stabilized.”

Should Update Physics Volume – “Whether or not the cached PhysicsVolume this component overlaps should be updated when the component is moved.”

Physical Materials

To use a Physical Material, you will want to modify a Material:
Open Material Editor >Select main Material Node > Details > Phys Material > Select target Physical Materials

To add a new Physics Material to the project:
Content Brower > Add New > Create Advanced Asset > Physics > Physical Material

Then adjust the properties of this new Physical Material:

Friction – How easy things can slide on the surface of this material

Friction Combine Mode – Average, leave alone

Override Friction Combine Mode – Can allow changing from Average to Min, Multiply and Max

Restitution – IMPORTANT; Defines how bouncy the surface is; how much energy is retained when it collides with another surface

Density – Materials will provide how much mass this materials will influence on the shape of the object. Higher the number, the heavier it will add. Measured as grams per cm3

APEX Destructibles

CREATE DESTRUCTIBLE MESHES!!! How cool is that? Use Nvidia APEX PhysX lab to create breakable meshes.

Alternatively, To create a destructible actor in UE4, use “Voronoi with a single depth level”. If you need more than one level of depth, it must be generated by APEX PhysX lab

Importing an APEX Destructibles and Cloth – Same as you would with an .FBX file. APEX assets have an .apb or.apx file extension.

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