Project240.net

Drifting - Aerobatics on Wheels

My interest in drifting originates from a fascination with rally drivers and the brilliant methods used to negotiate turns at very high speeds.  In rally, drifting is used because a large sideslip angle is said to produce large lateral forces due to build-up of loose road surface against the tire sidewall.  Drifting as a sport, however, is less concerned with turn performance and much more focused on the art of driving.  The challenge of drifting comes from a highly nonlinear and coupled tire response to side slip and longitudinal slip.  The front and rear wheels are made to operate in different parts of the traction regime through steering angle, driving/braking torque to the rear wheels, and of course, body-axis sideslip angle.
Drifting
Autocross
Photography
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On the Dynamics of Automobile Drifting
Mujahid Abdulrahim, University of Florida
SAE Paper 2006-01-1019
(click to download PDF manuscript)

Abstract
Driving at large angles of sideslip does not necessarily indicate terminal loss of control, rather, it is the fundamental objective of the sport of drifting. Drift racing challenges drivers to navigate a course in a sustained sideslip by exploiting coupled nonlinearities in the tire force response. The current study explores some of the physical parameters affecting drift motion, both in simulation and experiment. Combined-slip tire models are used to develop nonlinear models of a drifting vehicle in order to illustrate the conditions necessary for stability. Experimental drift testing is conducted to observe the dynamics featured in the track data. An accelerometer array on the test vehicle measures the acceleration vector field in order to estimate the vehicle states throughout the drift testing. Neural networks are used to identify the patterns in the accelerations that correspond to sideslip excursions during drifts. These estimates combined with computations of angular acceleration, yaw rate, and lateral acceleration build a framework for identifying the dynamics in terms of physical parameters and stability and control derivatives. The research developments are intended to support a future study quantifying the effects of vehicle configuration changes on drift capability as related to performance potential and handling qualities.

 

P_240_release2_video

Project_240 - Video release 2 - Low quality WMV [3MB]
Project_240 - Video release 2 - High quality MPG [17MB]

 		  Release 2 qualitatively summarizes the tests conducted at the Gainesville Raceway test track.  The video shows a short clip of a linked drift section from multiple perspectives.  The first viewpoint is an external, fixed-position camera following the vehicle maneuvering around a series of curves.  The video is shown in slow motion to emphasis the disparity between the attitude and velocity of the car.  The large angle of drift or sideslip is opposed by a steering input in the direction of slip (opposite to the direction of turning).  The car is then transitioned to left-turning drift to negotiate a sharp corner.

The following segment shows a MATLAB recreation of the drift sequence using data measured from the accelerometer array, angular rate sensors, and GPS sensor.  The simulated 240SX is superimposed on a composite aerial photograph of the test track.  Approximately 10 photos were captured from a Cessna 152 flying at 1000 feet above track level.  These photos were then manually stitched using Photoshop and geo-referenced in the simulation using known GPS points in the image.

The third segment shows the filtered data streams in sequence with a translucent drift video background.  The significance of the data in estimating sideslip angle is most apparent in the lateral acceleration data, which shows a clear disparity between the front and aft accelerations that is related to the drift angle.

The final segment illustrates the extent to which sideslip can affect lateral stability.  Here, a 360-degree translating spin is performed by inputting full steering deflection as the stabilizing moment begins to return the car to small sideslip.  The combined effect of the steering and the stabilizing forces produce a strong enough moment (and in turn a large enough angular momentum) to spin the car a full 360 degree turn.