Vehicle Controller
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This controller is used to create a wheeled vehicle like a car. The car body is a rigid body and each wheel is simulated by a raycast. The ray's intersection point is used to calculate the suspension length and the suspension force. The suspension force is used to stop the body from hitting the ground. For each wheel ray that hit the ground contact forces are also calculated and they drive and steer the car. Documentation links for vehicle controller in Bullet and PhysX. Settings below for Bullet.
Car Physics for 3D Games - 2011
Wheel Settings
wheelRadius : radi
Radius of the wheel. Should fit the render mesh of the wheel.
connectionPointCS0
Start of raycast relative to car body. The point where the suspension connects to the chassis.
wheelDirectionCS0
Direction of raycast relative to car body. Straight down is a good start. The length of the ray is m_suspensionRestLength1 + wheelRadius.
wheelAxleCS
Axis direction of wheel relative to car body. Selects what the zero direction is for wheel steering.
Suspension Settings
suspensionRestLength : restl
Whats the default position of the wheel if not in contact with ground. The maximum length of the suspension in metres. It's wheel center will then be at connectionPointCS0 + wheelDirectionCS0 * m_suspensionRestLength1.
m_maxSuspensionTravelCm : susp
The maximum distance the suspension can be compressed in centimeters.
m_suspensionStiffness : stiff
The stiffness constant for the suspension. How much force the suspension give on the chassi when the wheel is not in the default position. 10 - offroad buggy, 50 - sports car, 200 - F1 car.
currentLength = ray.distance - wheel radius
suspensionForce = stiffness * (restLength – currentLength) + damping * (previousLength – currentLength) / deltaTime
m_wheelsDampingCompression : comp
Damping coefficient when suspension is compressing. Set to k * 2.0 * sqrt(suspensionStiffness). k = 0.0 undamped and boyncy, k = 1 critical damping, k = 0.1 to 0.3 good values.
m_wheelsDampingRelaxation : relx
Damping coefficient when suspension is extending. This should be slightly higher then m_wheelsDampingCompression. k = 0.2 - 0.5.
m_frictionSlip : slip
Coefficient of friction between tire and the ground. 0.8 for real cars and higher for better handling.
m_rollInfluence : roll
0.0 = no roll, 1.0 = physical behaviour. High frictionslip then need to reduce this.
m_maxSuspensionForce : forc
Rigid Body
Mass
Mass of the vehicle. Typical values are 1500kg for a car.
Center Of Mass
The center of mass should be put in the lower part of the car to make it more stable and lower the risk of it flipping over.
Wheel Parameters
EngineForce
Positive if wheel drive forward and negative is back.
Brake
SteeringValue
The forward direction of the wheel with respect to it's default forward from wheelAxleCS.