Introduction to Robotics

1
Introduction to Robotics

• Chapter 2
• Class 3

2
The Vehicle Robot

• Most robots are mobile and can be considered
  vehicles.
• Two main types of vehicles are
• Wheeled
• Legged

3
The Wheeled Vehicle

• Advantages
• Simple to control
• Few stability issues
• Uses less energy per unit distance of motion than
  legged robots
• Disadvantages
• Limited to smooth terrain
• As surfaces get rougher, wheels must get larger
  and in turn use more energy

4
Designs

• The 4 wheel
• Traditional car-like design
• Two drive wheels and two steering wheels (usually
  at the front)
• Requires suspension system
• Poses design challenges when it comes to wheel
  speed and turning control

5
Designs ctd.

• The 3 wheel
• Usually, but not always, has two drive wheels and
  one steering wheel
• Eliminates the need for suspension, as 3 points
  of contact make a plane
• Still poses design challenges with regard to
  drive wheel speed and turning
• Usually leads to more complicated designs

6
Designs ctd.

• Other designs include
• Tracked vehicles such as tanks and backhoes
• Expansions on the 4 wheel idea, but with 6, 8,
  and sometimes more, parallel wheels
• An example is the six-wheeled Terragator
• Stanford and Illanator wheel systems
• Each wheel utilizes a hub with angled rollers
  to move, the gives the robot more maneuverability

7
Forces Acting on Wheels

• Power (in watts)
• A function of speed and transmission efficiency
• Motor Torque (in Newton Meters)
• A function of motor velocity and Power
• Others include air drag, and acceleration

8
The Legged Vehicle

• Advantages
• Can move where wheeled vehicles cannot
• Can maneuver stairs, trenches and inclines
• Disadvantages
• Energy constraints
• Complex designs
• Many moving parts

9
Classes of Legged Vehicles

• Statically stable
• At least 3 feet must be firmly placed on the
  ground and the center of gravity within the
  triangle formed by the feet.
• Dynamically stable
• The robot uses either the position of the body or
  the legs as a means to balance. It does not
  require 3 points of ground contact.

10
Mechanisms

• Many legged robots utilize hydraulics and
  pneumatic cylinders for stabilization and
  movement
• This can be seen in the, dynamically stable,
  hopper robots where legs are pushed out and
  retracted to simulate a hopping motion.
• Timing is essential for these motions and
  therefore, design and execution are difficult

11
Adaptive Gait Legged Robots

• Used for handling stairs and other unusual
  terrains.
• Utilize a pantomec leg mechanism
• A 3D Cartesian-coordinate pantograph to determine
  its orientation and maintain balance
• Posture sensors and touch sensors are also used

12
Energy Efficiency for Legged Robots

• Actuator action (and in turn power usage) falls
  into 3 categories
• Positive work mode when an actuator applies
  force to produce motion
• Isometric mode when force is applied, but no
  motion produced
• Negative work mode applying a braking or
  negative force
• An actuator that consumes energy in all 3 modes
  in the LEAST efficient

13
The Big Picture

• The two main types of vehicle robots each cater
  toward certain types of tasks
• Legged Robots may serve a greater application
  than their wheeled counterparts in the future,
  but as of now they remain largely in the design
  phase
• Energy management is perhaps the greatest hurdle
  that robots still need to overcome before entry
  into mainstream practical use.