Lect 9-10

Question 1

A manipulator arm versus a mobile robot?

Answer 1

A robot arm is fixed on the ground, and usually have a single chain of links.
A mobile robots motion is depending on the sliding and rolling constraints.
For the mobile robots, we need to integrate the motion of the robot in order to find the final position.
Mobile robots are also integrating the errors, therefore the final position maybe a bit different.

Question 2

What are non holonomic systems?

Answer 2

Assume one robot is going straight and then turns, and the other robot turns and then going straight. The distance achieved by the wheels are exactly the same but the final positions are not the same. Therefore integrating the motion in order to find the final position is not enough, we need to integrate it over time.

Question 3

What is the difference between kinematics and dynamics?

Answer 3

Kinematics does not take into account the acceleration,mass,forces. So every speed change is immediately applied.
In real world, robots uses dynamics, in dynamics we take into account the mass acceleration and forces.
Therefore when we take into account, the kinematics, when we say the robot to stop, it immediately stops.

Question 4

What are forward kinematics and inverse kinematics and why we are using the inverse kinematics in mobile robots?

Answer 4

Forward Kinematics: from the joint space to the world reference frame
Inverse Kinematics: From the world reference frame to the joint space.
Beucase of the non holonomic constraints in mobile robots we use inverse kinematics.

Question 5

How to describe a robots speed?

Answer 5

We need to take into account:
1) Wheel speed
2) Steering speed
3) Steering angle
4) Geometrical parameter.
In order to find the speed we need a function which takes into account these 4.

Question 6

What are the differences between a fixed wheel and a steerable wheel?

Answer 6

In fixed wheels, we can only control the speed.

In steerable wheels we can control speed and steering.

Question 7

What is a rotation matrix?

Answer 7

It maps the motion in global reference frame, interms of robot reference frame

Question 8

In curved motion what does R depend on?

Answer 8

R does not depend on the radius of the wheels, but on the distance between the wheels and on the angular speed.