Locomotion

The aim of this part of the course is to get an overview of the means by which a robot can move around.

Objectives

• Be able to explain basic principles for the following ways of locomotion
  • Legs
  • Wheels
  • Flying
• Use the kinematic model for a differential drive wheeled robot to calculate odometric position of the robot.

 

There are many other ways that a robot could move, such as crawling, swimming, etc but we will focus on the three mentioned above. Especially for flying and legged robots there is a lot more to say before you can actually make use of them but getting this level of detail is left for future studies.

I refer to the Springer Handbook of Robotics as SHoR. I will provide references to the 2nd edition of the book first and then in parentheses to the 1st edition.

 

 

Pre-Lecture Material

• Read the wikipedia page about differential drive kinematics Links to an external site.
• Read these slides Download these slides and this page on odometry Links to an external site.
• Look at the video on the front page of https://leggedrobots.org Links to an external site.. and read the text below including the topics studied.  
• Read the Self-study material with general drone knowledge (section 6) Links to an external site. (in Swedish in chapter 6 of this pdf Links to an external site.)
  • The English version of the drone material is from Finland. The websites with information about about NOTAM and AIP are specific to each country. You find the Swedish equivalent in the Swedish version of the text in section 2.2.

 

Wheeled robots

SHoR chapter 24 and section 29.1 (17 and section 20.1)

Wheels is the most common way to implement a locomotion system in a robot. It is simple and efficient.

Wheel types (SHoR Fig 24.2 and 24.3 (17.2))

• Passive fixed, passive or active off-center orientable, active orientable without offsets
• Swedish wheel 
  • Purpose of the rollers?
  • Angle of rollers?
  • How to make the robot move?
  • Robot with Swedish Wheels, DLR Links to an external site.

Kinematic Constraints (SHoR 24.2.2 (17.2.2))

• What does it mean that a robot is holonomic?

Wheeled Robot Structures

Get an overview from SHoR 24.3 (17.2). You should know the two-wheel differential drive robot configuration well and understand the concept of an omnidirectional/omnimobile robot.

Odometry (SHoR 29.1 (20.1))

• What is it?
• Be able to use for differential drive robot
• Real world challenges?

 

Legs

SHoR Chapter 17 (16) 

• Gait
• Static versus dynamic stability
  • RoboCupUS - Static vs dynamic walking Links to an external site.
  • Notice how the slower of the two robots (statically stable) always ensure that the centrer of mass rest above one of the feet.
• Configurations with 2, 4, 6, 8, ...
  • Pros and cons? Static vs dynamic stability? 
• Pros and cons with legs?

Flying

Flying allows the robot to move in 3D. This can sometimes simplify navigation as we can simply fly over obstacles. Flying robots are often referred to as drones or UAV (unmanned aerial vehicles). One of the main challenges for these types of robots is the energy storage. Batteries are heavy and adding more batteries may not pay off as this also increases the weight and the drone thus draws more power to stay in the air. 

Look at

• Fixed-wing
  • Normal airplane is an example
  • Can glide which makes it relatively power efficient
  • Take-off and landing requires quite bit space (landing sometimes with parachute)
  • Cannot stand still in the air
• Rotary-wing / Multi-rotor
  
  • Helicopter most common example
  • Most autonomous flying robots have more rotors, often 4 or 6
  • High manoeuvrability (can stand still in the air, can take off vertically, etc)
  • Limited range 
• Applications (SHoR 26.8.2-3 (44.3))
• Challenges for Autonomous UAS (SHoR 26.7.1 (44.4))