Chaos Modular Vehicles Quickstart

This guide explains how to set up a modular vehicle for simulation in the Chaos Physics Solver.

The individual assets that make up a modular vehicle are as follows:

• Geometry Collection assets (for the vehicle parts - generated from Static Meshes)
• A vehicle Blueprint

Enable the Chaos Modular Vehicle Plugin

Click Edit > Plugins and search for "chaos modular vehicle". Verify the Chaos Modular Vehicle plugin is enabled for your project.

This is an entirely separate plugin from the Chaos Vehicle Plugin. You do not require both.

(Optional) Enable the Chaos Modular Vehicle Examples Plugin

Click Edit > Plugins and search for "chaos modular vehicle examples". Verify the Chaos Modular Vehicle Examples plugin is enabled for your project.

Enable the network settings

In your project settings, under Engine > Physics, click Enable Physics Prediction and Enable Physics History Capture. This gives superior networking with server authoritative client prediction with rewind resimulation behavior. The vehicle will feel like it is locally controlled with no lag from the control inputs.

Create the Geometry Collection Assets

The modular vehicle currently uses Geometry Collection assets for the vehicle parts. This is the same asset that is used with physics destruction. The destruction tools can be employed to generate geometry collections from static meshes.

Convert each of the separate vehicle pieces from a static mesh to a Geometry Collection using the fracture tools, following these steps:

1. Drag a static mesh onto a level, and change the editor to Fracture Mode in the Main Toolbar.

   

2. With the static mesh asset selected, click Generate > New.

   
3. In the Select Path window, choose a location where to save the new asset and name the asset.
4. Click Generate Geometry Collection.

5. In the Details for the Geometry Collection asset, set the mass of each part and the damage threshold for how easily the part breaks off.

   

Repeat these steps for all other vehicle parts. You need at least two assets: an asset for the vehicle chassis and an asset for the wheel.

Create a Cluster Union Vehicle Pawn Blueprint

1. In the Content Browser, click Add (+) > Blueprint Class.
2. In the Pick Parent Class window, under All Classes, search for "ModularVehicle" and select ModularVehicleClusterPawn.
3. Click Select.

The new asset appears in the Content Browser. Give it a recognizable name so that you can easily locate it later (for example, "BP_ChaosFrontWheel").

Build The Vehicle Structure in The Blueprint

Now that you have created the Modular Vehicle Blueprint, open it in the Blueprint Editor and begin adding the Geometry Collection Components. The Cluster Union Vehicle Pawn has some default components already assigned: a Vehicle Simulation Component responsible for the modular vehicle simulation, as well as a Network Physics Component.

1. Add Geometry Collection components for each of the vehicle pieces by dragging each Geometry Collection asset into the Components panel under the Cluster Union Vehicle Component.

   

2. Use the Viewport to position the vehicle parts so they sit in the correct position relative to one another. For accuracy, it may be better to enter the precise location for pieces into the Details panel of the Geometry Collection component. This is particularly important for the wheels, as if they are not perfectly symmetrical, the simulation might not drive in a straight line. The convention is X forwards, Y right, Z up.

   

3. In the Details panel, under Chaos Physics > Clustering, enable Force Update Active Transforms. If you don’t do this, then pieces that fall off the vehicle will follow the main actor around once they come to rest. This is due to an optimisation that will stop updating the transforms when the object is not moving. Ordinarily this is fine if the geometry collection has its own actor, however here we are parented to a shared moving actor.

When using one wheel model for the entire vehicle, you might want to flip the wheels on one side of the vehicle for the wheels to look correct. This involves adding a 180 backdegree rotation to the Z rotation axis. This flipping of the axes will also require a change in the next step of this guide, when you set up of the simulation components associated with these parts.

Add Simulation Components to the Geometry Collections

Simulation components add simulation behaviors to the geometry collections. For example, if you want a geometry collection to behave like a wheel, you need to add a Wheel component.

In the Blueprint Editor, click Add (+) and search "sim" to get a list of all the available simulation options.

The hierarchy of the simulation components is very important. Simulation components should be a child of their parent geometry collection. For example, a VehicleSimWheel Component must be added under a Geometry Collection wheel model. The simulation uses the transform of that component to locate where the forces should be applied from, and also to turn off the simulation for that part if it is broken off. The parent-child relationship of the simulation components themselves is also important. The parent-child relationship of engine, clutch, transmission indicates the flow of torque between the modules.

To add simulation components to the geometry collections, follow these steps:

1. Add a VehicleSimSuspension component under each of the geometry collection components that represents a wheel.
2. Add a VehicleSimWheel component under each VehicleSimSuspension component.
3. Add a VehicleSimEngine component under the vehicle chassis geometry collection component.
4. Add a VehicleSimClutch component under the VehicleSimEngine.
5. Add a VehicleSimTransmission component under the VehicleSimClutch.

The finished setup should look like the following image.

Change all the simulation parameters in the details panel as appropriate for your vehicle. It is possible to change parameters on multiple wheel components simultaneously by holding Ctrl while selecting the components. Then, any changes you make in the details panel will apply to all of the selected components.

If a wheel component has been rotated in the editor to make it look right (180 degree rotation around Z) then the wheel will simulate backwards unless the Reverse Direction property is checked.

Define Vehicle Inputs

1. Create input actions for each of your controls.

   

2. For the Steering input action, it is advisable to add a Dead Zone modifier, otherwise the steering might drift when it should be driving straight.

   
3. In the Content Browser, click Add (+) > Input > Input Mapping Context.

4. Open the input mapping context and map controls to your each of your input actions, as shown in the following images.

   

5. On the vehicle asset, inputs are defined by name and type. These need to match the names implemented in the modular vehicle code. The core modules use the following inputs:

   Module	Input Name
   Engine	Throttle
   Clutch	Clutch
   Thruster	Throttle
   Transmission	ChangeUp, ChangeDown
   Wheels	Steering, Brake, Handbrake
   Aerofoil	Roll, Pitch, Yaw

6. On the Vehicle Simulation component, add five array members to the Vehicle Input section if they do not already exist, and fill them out in the Details panel on the right.

   

7. In the vehicle Blueprint, connect the EnhancedInputAction events to the vehicle as shown in the following image.

   

(Optional) Set up a Camera and Spring Arm

You might want to set up a camera that follows the vehicle.

1. Open the vehicle Blueprint.
2. In the Components window, click Add (+) > Camera.

3. Use the Viewport in the Blueprint Editor to position the camera. In the following image, the camera is positioned behind, slightly raised, and tilted down towards the vehicle.

   
4. With the Camera component selected, verify that Use Pawn Control Rotation is disabled. This ensures that the camera is locked to its view direction, rather than the Player Controller's view direction.

Drive a Skeletal Mesh from a Modular Setup

1. Right-click in the Content Browser and click Animation > Animation Blueprint.
2. Click the skeleton you want to use.
3. In the Parent Class tab, click ModularVehicleAnimationInstance.
4. Click Create.
5. In the Content Browser, name your animation blueprint.

6. Open the animation blueprint and create a Modular Vehicle Controller node and connect it up as shown in the following image.

   
7. Add your vehicle skeletal mesh to the vehicle Blueprint.
8. On your skeletal mesh component, ensure the animation mode is set to Use Animation Blueprint, and set the Animation Class to your newly-created animation blueprint.

9. In each of the modular vehicle simulation components (wheels and suspension), enter the Bone Name for the bone you wish to animate in the skeleton mesh.

   

Create a ModularVehicleGameMode Blueprint

If you want to spawn the vehicle instead of a character when you start a game then you will need to create a vehicle game mode and assign this in the world settings.

1. In the Content Browser, click Add (+) > Blueprint Class.
2. In the Pick Parent Class window, click Game Mode Base.
3. In the Content Browser, double-click to open the new Game Mode Blueprint in the Blueprint Editor.
4. In the Details panel under Classes, set the Default Pawn Class to your vehicle Blueprint.
5. Click Save and then close the window.
6. In the Main Toolbar window, click Settings > World Settings
7. In the World Settings panel, under Game Mode, set the GameMode Override to your Game Mode Blueprint.

Modules Overview

Simulation Modules Overview

Example Vehicles

Here are some examples of vehicles that could be created using the simulation modules:

• Traditional Automobile: Engine, Clutch, Transmission, Wheel, Suspension
• Unpowered Trolly: Wheel, Suspension
• Simple Arcade Vehicle: Thruster, Wheel, Suspension
• Aircraft: Thruster, Aerofoil, Wheel, Suspension
• Hovercraft: Suspension, Thruster, Aerofoil. (A suspension without wheels acts just like a hovercraft skirt, and an aerofoil could act as a rudder.)

Module Setup Parameters

The following tables describe the setup parameters of each of the simulation modules.

Wheel Setup Parameters

Suspension Setup Parameters

Engine Setup Parameters

Transmission Setup Parameters

Clutch Setup Parameters

Thruster Setup Parameters

Aerofoil Setup Parameters