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shadowmage45 edited this page Nov 30, 2016 · 2 revisions

KSPWheel - Force Based Wheel Collider

Replacement for U4 wheel collider, geared for use in KSP.


  • Simple Component driven wheel collider system.
  • Multiple WheelColliders may be added to any model hierarchy or single game object.
  • Wheel colliders have no limitations on their orientation.
  • Wheel colliders may add forces to an arbitrary specified rigidbody, not necessarily the one closest to their parentage.
  • Wheel colliders may be easily enabled/disabled.
  • Wheel colliders may have -any- and -all- parameters changed during run-time, without any unexpected side effects.
  • Wheel collider physics updates are manually issued by the controller class, so all update ordering can be user controlled
    • Can optionally be set to 'auto-update', in which case it will fire updates in its own FixedUpdate
  • Configurable suspension sweep type - simple raycast (fastest, least accurate), sphere-cast (fast, very accurate for wide wheels), or compound capsule-cast (not as fast as the others, but potentially very accurate)
  • Configurable friction curves to simulate various tire types and properties.
  • Static friction ensures there is no unwanted sliding.
  • Supports 'zero-length' suspension setups by using stand-in colliders with standard friction.
    • Most other wheel functions will be disabled (motor, brakes, steering) as no friction force information is available.
    • Intended for use as a toggle on landing legs, but might have use on some wheels as well.
    • WIP -- Investigating solutions to calculate friction for solid suspension setups, which would allow for steering/motors/etc.

Typical Use:

  • Requires one or more user supplied 'Vehicle Controller' scripts/components to enable/disable colliders, sample input states, and update wheel torque/brake status. This script could function on a per-part or per-vehicle basis, depending upon user needs.
    • This script can manage one or more wheel colliders.
    • For use in KSP the VehicleController script should remove any U5 WheelColliders and replace them with the KSPWheelCollider component.
    • A fully functional set of PartModules for KSP are included that should be configurable for most wheels.
  • WheelCollider is responsible for all physics updating, managing sticky friction, bump-stop handling.
  • Several parameters require updating on every tick if they vary from the defaults; these should be set prior to the wheelCollider.updatePhysics() method being called:
    • brake torque
    • motor torque
    • steering angle
    • local gravity
  • Uses manual-update methods -- allows for grouping and batching of wheelCollider updates when multiple wheels are on the same part/vessel.


  • Add KSPWheelCollider component to a game-object; either through the Editor, or at runtime.
  • Setup the following fields on the new WheelCollider (mandatory, needed for basic functionality):
    • rigidbody -- the rigidbody to apply forces to. MUST be setup or the wheels will have no effect.Defaults to 'false', requiring external update calls.
  • Optionally setup the following fields on the WheelCollider:
    • preUpdateAction - the pre-update callback (optional)
    • postUpdateAction - the post-update callback (optional)
    • autoUpdate - should wheelcollider update itself in FixedUpdate, or rely on manual external update calls?
    • friction curves
    • friction coefficients
    • suspensionSpring
    • suspensionDamper
    • wheelRadius
    • wheelMass
    • suspensionSweepType -- ray, sphere, capsule (WIP, working but needs additional options for CAPSULE type)
    • physicsModel -- standard, alternate1, alternate2 (WIP, Not yet implemented)
  • On every physics update the controller script should update the following fields either prior to calling the wheelCollider.physicsUpdate() method, or in the pre-update callback (if they have changed from previously set values):
    • gravity vector
    • motor torque
    • brake torque
    • steering angle

Source Code License

Source code for this project is currently licensed under All-Rights Reserved; please ask if you wish to make use of this code. Once initial development has finished it will be released under the most appropriate liberal open-source license(s) that I can find (aiming to not cause any license issues with any re-use; might even just become public domain).

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