Anyone who worked with chaos vehicles knows that getting a Chaos Vehicle right can be more frustrating than fun. The learning curve is steep and one will spend hours just trying to find out what is wrong.

I found that there is insufficient information to do effective trouble shooting as you have to squeeze out a few key infos from hours of different tutorials. I wrote this article as summary of my findings.

In this concise guide you will learn to understand, identify and quickly solve common problems with rigging your own vehicles using the Chaos Vehicle Plugin, applicable for Unreal Engine 5.3.2.

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Chaos Vehicle Creation Guidelines

To rig a functioning chaos vehicle, pay close attention to a few important guidelines. Getting just one wrong will lead to undesired behavior guaranteed. These are the ones I figured out during my research.

• the front side of each wheel has to face X-Axis
  
• the front side of the vehicle has to face X-Axis
  
• all wheels need to be their own object
  
• wheels need their object center in the center of their geometry
  
• all wheel centers/axles need to sit directly on X-Axis and Y-Axis
  
• all wheel bones need to have the proper rotation, with X-Axis as front, Y-Axis as right side, Z-Axis as top.
  
• both mesh and armature need to be exported

Chaos Vehicle .FBX Export

When exporting a vehicle rig, the armature and all its mesh components need to be selected during export. With the below shown export setting, any unit adjustment should be superfluous as of Unreal 5.3.2. If this ever makes issues, the scaling unit of your 3D program needs to be adjusted to Unreal Engine.

Chaos Vehicle Troubleshooting

Symptoms:

• Chaos Vehicle does not move
• Chaos Vehicle Wheels are clipping through terrain
• Chaos Vehicle Wheels aren’t rotating in the right direction

This happens when the wheels do not to touch the ground properly where they normally create forward motion. Instead, the wheels clip through terrain, with your vehicle resting on its car body.

Causes:

• wheel bones are not properly aligned during export.
• vehicle is not properly aligned during export
• bone hierarchy is not correct

Fixes:

• for wheels, in your 3D program: rotate armature and/or bones until wheel front is facing towards X-Axis. To double check whether you did everything right, import the model into Unreal Engine, go to its Physics Asset and open Physics Asset Editor
• for vehicle, in your 3D program: rotate your vehicle as follows: X = front, Y = side, Z = up
• make sure the axis alignment is also reflected in the export settings in both cases
• make sure all bones have the following hierarchy once imported into unreal:
  • Root
    • Wheel Rear Left
    • Wheel Rear Right
    • Wheel Front Left
    • Wheel Front Right

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Symptoms:

• Chaos Vehicle keeps moving as if it’s sitting on a hidden sphere

Causes:

Your vehicle’s wheel centers are most likely off.

• this is not visible from standard UE debug collision view, as Chaos Vehicles appear to have their own collision shapes
• I suspect that problems with wheel centers can be caused e.g. by older versions of blender, where the .fbx export plugin does not properly apply wheel transforms and spawns them at origin instead
• unlikely but possible: in UE, check the radius configured in wheel blueprint and turn it down

Fixes:

• double check your export parameters
• check if wheel centers are configured properly
• in UE, turn down the wheel radius of your wheel blueprints
• If issue still persists, define each wheel offset manually (copy wheel transform from 3D program into UE -> Vehicle Pawn -> Details -> Wheel Setup) as workaround

Useful Tutorials

Here I want to honor a few handy tutorials that helped me understand Chaos Vehicles and compile this guide as a result.

• How to rig vehicle in Blender 2.8 for UE4 on continuebreak.com
• UE Chaos Vehicle Documentation