Two to Four: Bicycle model for Car

Archit Rastogi
7 min readAug 16, 2020

Lateral dynamics

For the control of lateral motion of the vehicle, it is critical to model the lateral dynamics. Lateral motion control is used in various ADAS features like lane centering, lane keeping etc. The lateral dynamics models are also imperative in modeling vehicle behaviours during the lateral manoeuvres and can be used to study and design the system and components.

In order to calculate accelerations and velocities in different directions of interest, it is necessary to define the axis systems. Generally axis system can be Earth fixed or Vehicle fixed.

Earth Axis System

Earth fixed axis system has X,Y (horizontal) and Z (vertical) as principal directions in global coordinates. The following figure shows a vehicle location and other properties like heading angle in the earth or global coordinates.

Earth fixed Axis System

Vehicle Coordinate System

This is fixed to the vehicle. X is longitudinal direction, Y is lateral, Z is vertical. Origin is at CG of the vehicle. The rotational motion along vehicle X is called roll.

Bicycle Model