Sensors and Methods for Mobile Robot Positioning

Chapter 1: Sensors for Dead Reckoning 25
Figure 1.11: The Denning Sentry (foreground) incorporates a three-point synchro-drive
configuration with each wheel located directly below the pivot axis of the associated steering
column. In contrast, the Cybermotion K2A (background) has wheels that swivel around the
steering column. Both robots were extensively tested at the University of Michigan's Mobile
Robotics Lab. (Courtesy of The University of Michigan.)
D 2%N R
C e
e
(1.12)
where
D = vehicle displacement along path
N = measured counts of drive motor shaft encoder
C e = encoder counts per complete wheel revolution
R = effective wheel radius.
e
1.3.5 Omnidirectional Drive
The odometry solution for most multi-degree-of-freedom (MDOF) configurations is done in similar
fashion to that for differential drive, with position and velocity data derived from the motor (or
wheel) shaft encoders. For the three-wheel example illustrated in Figure 1.12, the equations of
motion relating individual motor speeds to velocity components V xand V yin the reference frame of
the vehicle are given by [Holland, 1983]: