Mobile Robots

Behaviors:

Mobile Robots Models:

(a) Differential Wheel Drive Model     --> Used for implementation (real model)
(b) Unicycle Model                               --> Used for design (more simple)

The following snapshot, is taken from the Glue Lecture of Lecture 2 of the Coursera course: Control Of Mobile Robots

where,

• νr, νl: the angular velocities of the right and left wheel
• c: the velocity of the robot
• R: the radius of each wheel
• Ф: the angle between the x axis and the robot direction
• ω: the angular velocity of the robot (rate of change of Ф)

So, what we do is:

• Use the Unicycle model for design (get: ν,ω)
• Convert to the Differential Wheel Drive model from implementation (solve above equations -> get νr, νl from ν,ω )

Wheel Encoders:

They are wheel ticks counter, where the wheel has N ticks per revolution.
The wheel encoder counts the number of wheel ticks elapsed during rolling.

Knowing previous x,y,Ф and the readings of the wheel encoders, we can get the current x,y,Ф as follows:

The following snapshot, is taken from the Glue Lecture of Lecture 2 of the Coursera course: Control Of Mobile Robots

But, if the robot slipped, for example because it hit another robot, then its movement will not be related to the wheel encoder reading!

in this case, we shall use sensors (IR - Ultrasonic - LaserScanner - Camera - ...etc)

Behavior:

The robot may have one or more controllers (behaviors):

• Go-To-Goal
• Avoid-Obsatcles
• Track-Target
• ...etc

Mobile Robot Control Block Diagram:

The following snapshot, is taken from the Glue Lecture of Lecture 2 of the Coursera course: Control Of Mobile Robots