The indirect calculation of heading angle through wheel speed difference is a simplified version of the classic "wheel speed odometer" method in vehicle dynamics. The core principle is to use the speed difference between the left and right wheels, combined with the vehicle's wheelbase, to calculate the angular velocity of the vehicle rotating around the vertical axis, and integrate it to obtain the heading angle.
The specific implementation method is as follows:
(1) Calculate instantaneous yaw rate based on the linear velocity of the left and right wheels
Read the left rear wheel speed 
and right rear wheel speed 
(unit: rad/s), and calculate the linear velocity of the left and right wheels based on the wheelbase L (unit: m) and tire rolling radius r (unit: m): ; 
;
Directly using this formula will face many practical problems in reality, and algorithm level correction of steering geometry and compensation for sideslip and nonlinear regions are also required. Steering geometry correction (Ackermann steering geometry) typically uses the wheel speed of the non steering axis (usually the rear axle) to calculate the rate of change in heading angle. Side slip and nonlinear compensation usually involve the fusion of wheel speed difference calculation with IMU (Inertial Measurement Unit) gyroscope data (such as Kalman filtering), using wheel speed difference to correct the gyroscope's zero bias drift, and using the gyroscope to compensate for the dynamic delay of wheel speed calculation.
(1) Signal processing
When driving at low speeds, the speed difference between the left and right wheels is very small. If the resolution of the wheel speed pulse counter is insufficient, it will cause the calculated heading angle change rate to jump severely. Low pass filtering is required to remove high-frequency noise using first-order low-pass filtering.
(2) Integrating to calculate heading angle
In this way, high-precision estimation of heading angle change rate can be obtained solely through wheel speed sensors under low-speed and quasi-static conditions, which is of great value for short-term positioning and Dead Reckoning.
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