In the final chapter we focus on motion planning
and control of wheeled mobile robots that
move without skidding on hard flat surfaces,
such as this differential drive robot, which
moves by independently controlling the rotation
of two conventional wheels, and this omnidirectional
mobile robot, which moves by independently
controlling the rotation of mecanum wheels,
which allow sideways slipping.
In all cases, we assume that we control wheel
velocities, not torques, so we have a kinematic
model mapping wheel speeds to the chassis
velocity.
The planar configuration of the robot chassis
is written T_sb, an element of SE(2), or simply
as the vector q equal to (phi, x, y), where
phi is the heading angle of the chassis and
(x,y) is the position of a reference point
on the chassis.
The velocity of the chassis is written either
as the planar twist V_b, expressed in the
body frame {b}, or as the time derivative
q-dot.
For a nonholonomic mobile robot, like the
differential drive, the space of feasible
chassis velocities is only 2-dimensional,
because the robot cannot slide sideways.
For an omnidirectional robot, the chassis
can move in any direction in its 3-dimensional
velocity space.
This chapter addresses the following issues
for omnidirectional and nonholonomic wheeled
robots:
Kinematic modeling for several different types
of wheeled mobile robot.
Motion planning for wheeled mobile robots.
Feedback control to stabilize motion plans.
Odometry, to estimate the configuration of
the chassis based on data from the wheel encoders.
And mobile manipulation, where the wheeled
mobile base is equipped with a manipulator.
In particular, we derive the Jacobian mapping
wheel and joint velocities to the end-effector
twist, and we use this to develop a coordinated
controller for the mobile base and robot arm.
In the next video we begin our study with
omnidirectional wheeled mobile robots.
