Development of an Ackermann steering autonomous vehicle
Project Resources
- Objective: The objective of this project was to create an Ackermann steering based self driving car in Duckietown.
- Approach: Increasing the complexity (and realism) of the hardware chassis, from differential drive to Ackermann steering.
- Authors: Merlin Hosner and Raphael Fröhlich
Why Ackermann steering?
Ackermann steering is a configuration of wheels on a vehicle charachterized by four wheels, two in the back that are powered by a DC motor, and two in the front that steer though commands received by a servo motor. In contrast, differential drive robots have two wheels that are independently powered by two DC-motors, with a passive omnidrectional third wheel that acts as support.
The dynamics (i.e., the “kind of movement”) of differential drive robots is quite different from real world automobiles, which, e.g., cannot turn on the spot. Ackerman steering achieves more realistic vehicle dynamics at cost: increased hardware complexity and mathematical modeling. But neither of these challenges have stopped talented Duckietown student from designing and implementing an Ackermann steering Duckiebot!
(Duckietown trivia: careful Duckietown observers will have noticed that the Duckiebot models historically have been called DB18, DB19, DB21, etc. – every wondered which would have been the DB20?)
Ackermann steering in Duckietown: the challenges
Ackermann steering introduces more complex mathematical modeling, with respect to differential drive robots, in order to predict future movement hence elaborate pose estimates on the fly. The kinematic modeling of the front steering apparatus is non trivial, and the radius of curvature Ackermann steering robots showcase is very different from differential drive robots.
Differential drive robots are capable of turning on the spot (applying equal and opposite commands to the two wheels), while anyone who has ever tried parallel parking a real car, knows that this is not possible.
How complex will it be for Ackermann steering robots to navigate Duckietown is the real challenge of this fun project.
The authors start from basic design elements through CAD, iterate through various bills of materials, make prototypes, and program them leveraging the Duckietown software infrastructure to achieve autonomous behaviors in Duckietown.
Project Highlights
Here is the output of their work. Check out the documents for more details!
Ackermann steering: Results
(Turn on the sound for best experience!)
The autonomous behaviors of the Ackermann steering Duckiebot, a.k.a. DB20 or DBv2, shown above are the work of Timothy Scott, a former Duckietown student.
Ackermann steering Duckiebot: Authors
Merlin Hosner is a former Duckietown student in the Institute for Dynamic Systems and Controls (IDSC) of ETH Zurich (D-MAVT), and currently works at Climeworks as a Process Development Engineer.
Rafael Fröhlich is a former Duckietown student in the Institute for Dynamic Systems and Controls (IDSC) of ETH Zurich (D-MAVT), where he is currently a Research Assistant.
Learn more
Duckietown is a modular, customizable and state-of-the-art platform for creating and disseminating robotics and AI learning experiences.
It is designed to teach, learn, and do research: from exploring the fundamentals of computer science and automation to pushing the boundaries of knowledge.