Ackerman Steering

Ackerman Steering

Used almost exclusively in the automotive industry, Ackerman steering is designed to ensure that the inside front wheel is rotated to a slightly sharper angle than the outside wheel when turning, thereby eliminating geometrically induced tire slippage. As seen in Figure 1.8, the extended axes for the two front wheels intersect in a common point that lies on the extended axis of the rear axle. The locus of points traced along the ground by the center of each tire is thus a set of concentric arcs about this centerpoint of rotation P , and (ignoring for the moment 1 any centrifugal accelerations) all instantaneous velocity vectors will subsequently be tangential to these arcs. Such a steering geometry is said to satisfy the Ackerman equation [Byrne et al., 1992]:

satisfy the Ackerman equation

For the sake of convenience, the vehicle steering angle 2SA can be thought of as the angle (relative to vehicle heading) associated with an imaginary center wheel located at a reference point P2 as shown in the figure above. 2 SA can be expressed in terms of either the inside or outside steering
angles (2i or 2o) as follows [Byrne et al., 1992]:

outside steering

Ackerman steering provides a fairly accurate odometry solution while supporting the traction and ground clearance needs of all-terrain operation. Ackerman steering is thus the method of choice for outdoor autonomous vehicles. Associated drive implementations typically employ a gasoline or diesel engine coupled to a manual or automatic transmission, with power applied to four wheels through

typically employ a gasoline or diesel

a transfer case, a differential, and a series of universal joints. A representative example is seen in the HMMWV-based prototype of the USMC Tele-Operated Vehicle (TOV) Program [Aviles et al., 1990]. From a military perspective, the use of existing-inventory equipment of this type simplifies
some of the logistics problems associated with vehicle maintenance. In addition, reliability of the drive components is high due to the inherited stability of a proven power train. (Significant interface problems can be encountered, however, in retrofitting off-the-shelf vehicles intended for human drivers to accommodate remote or computer control.)

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