Liling Liu
- Nov 17, 2023
- 3 min read

[Chaos Physics] Unreal Engine 5.2 物理約束可掛接拖車車輛教學｜Physics Constraint Hitchable Trailer

Physics Constraint Hitch-able Trailer

Here to use Driving Chaos Vehicle Projects to make hitchable trailer

Import Mesh and Texture: Crab the model and texture into Browser

Trailer already rig and skin

FBX import Options:

Skeletal Mesh: turn on

Combine Meshes: If you have many separate mesh, you could turn on

Plugins:

ChaosVehiclesPlugin

WheeledVehiclePawn

Create BP:

Right click mouse > Blueprint Class

All Classes:

search: vehicle

Select “ WheeledVehiclePawn ”

Mesh > Skeletal Mesh Asset > trailer

Wheel Setup

Select Vehicle Movement Component

This trailer has two wheels so Press 2 times to add

Wheel Setup > Wheel Setups > +

Go to Skeleton and copy bone name

Select the bone > right click > Copy selected Bone Names

Paste to Wheel setups index bone name

Turn on Simulate Physics

Trailer Physic

Open physics Asset

Select physic and delete

Because the default physic shape is not fit for the trailer

Select wheel bones > Primitive shape: Sphere >Add bodies

Select Root bone > Primitive shape: Single convex Hull >Add bodies

Input Action

Project settings

Go to Engine - Input

Action Mappings: Interact--> T

Animaton

Obtain the behaviors we want for our vehicle.

Select trailer skeleton > right click mouse > Create > Anim Blueprint

Opne AnimBP > Class Settings > class options > Parent Class : Vehicle Animation Instance

Mesh Space Ref Pose: this is used to return the mesh space reference pose for our skeletal mesh in the Animation Blueprint

Wheel Controller : offloading a lot of the work in creating these types of animations, you can use the Wheel Controller Node to drive the animations.

GO to BP_trailer

Select Mesh > Animation > Anim Class : ABP_trailer

Prepare Interaction Object

Open BP_CAR

Add Collision, and naming: Docking.

Blueprint > Blueprint Interface

A Blueprint Interface is a collection of one or more functions - name only, no implementation - that can be added to other Blueprints. This is essentially like the concept of an interface in general programming, which allows multiple different types of Objects to all share and be accessed through a common interface.

Functions: Interact

Inputs: car (BP_Car, object reference)

Open BP_car

Use for loop to check does implement interface, if true, does interact

Opne BP_Trailer

Add Collision

Naming: Trigger_coli

Add PhysicsConstraint

A physics constraint is a joint that allows you to connect two Actors or component together and also apply limits or forces on them.

Constraint

Conponent name 1: Mesh

Conponent name 2: Trigger_coli

Control Physics constraint - Angular Limits

Swing 1 motion (Z) : Limited, swing 1 limted: 60

Swing 2 motion (x): Locked

Twist motion (y): Locked

Add Text Render

1. Text: type the information.

2.Turn off visibility

Add cube

In order to let trailer to stand on the ground, so add cube

Add Interface

Class Settings > Implemented Interfaces > select BI_Interact

Add variables:

1. CanHitch :Boolean

2. TryHitch : Boolean

Select trigger_collision box add begin overlap and end overlap

When End overlap, try Hitch: turn off, and text does not show

When begin overlap, try Hitch: turn on

Get car docking and trailer trigger_coli’s world location and do float to integrate value

Does car docking X subtract trailer trigger X to get the value. The value is less equal what we want the value. However, we might be get the negative value, so here I use ABS to get positive value.

Does car docking Y subtract trailer trigger Y to get the value. The value is less equal what we want the value.

X and Y value both are true and return true.

Set true/false to can Hitch