tyre simulation

simulation of tyre motion for tbd car game

Unity 6 project

a build in folder builds

• left click mouse to open values tweak menu

requires Unity AssetStore assets to be put in folder Unity project/Assets/Third-Party:

• Easy Tweak (https://assetstore.unity.com/packages/tools/gui/easy-tweak-162205)
• Quick Outline (https://assetstore.unity.com/packages/tools/particles-effects/quick-outline-115488)

YouTube demo: https://youtu.be/foVWJFGZllQ

current state

tyre physics implemented:

• linear momentum
• spring effect (dampened spring + visual deformation)
• rotation due to linear momentum on contact
• friction (air, roll, transversal slip)

not implemented (yet):

• roll due to gravity (downhill roll behaviour observed is due to spring effect, gravity, rotation due to linear momentum on contact and friction)
• angular momentum from inertia due to transversal tilt on contact
• tyre to tyre contact

tyre properties:

• radius 0.991199m

• width 1m

• weight 40kg

• pressure 0.25

• dampening 1200

• spring constant 30000

spring code excerpt:

// tyre acts like dampened spring
// dampen force is proportionally tyre movement in spring force dir as long as tyre surface contacts the ground
// spring force dir is tyreSquishForceDir
// when tyre surface looses contact to ground, tyre surface stops moving as spring instantly (this is an approximation here)
// springTyreAcceleration is acceleration of the whole tyre due to the acting like a spring
min = radius to tyre surface indentation
tyreSquishForceVal = (tyreRadius - min) / unitTyrePressure;
springTyreAcceleration = (tyreSpringConstant * tyreSquishForceVal - dampening * Vector3.Dot(velocity, indentationDir)) * indentationDir / tyreMass;


static Vector3 gravity = new Vector3(0, -9.81f, 0);
const float airFrictionCoefficient = 0.01f;
const float rollFrictionEarthRubberCoefficient = 0.0013f;
const float slideFrictionEarthRubberCoefficient = 100.0f;