Independent Wheel Offset Steering (IWOS): A New Locomotion Concept for Mobile Robots

Mobile robots with differential drive are common in warehouses, factories and spaces they share with people. This project develops and tests Independent Wheel Offset Steering (IWOS), a new locomotion system that builds on differential drive but gives the robot more freedom of movement. The work builds on the concept described in the 2018 patent application A 502321/2018 – Mobiles System by TU Wien, Markus Bader and George Todoran.

IWOS uses two actuated caster-like wheels, one on each side. On each, both the fork and the wheel are steered independently, and a passive caster wheel keeps the robot stable. The fork's range of motion is limited, but it still makes the robot noticeably more maneuverable while keeping the hardware and software simple. Most importantly, the robot can face a different direction from the one it's driving in. This lets it copy a familiar human habit: looking where you're about to go. Its heading becomes a visible cue that tells people nearby where it's headed, which helps human–robot interaction and could improve how it detects and handles collisions.

Structure of the IWOS: left and right steering joints with wheel offset s, wheelbase l, and a free-spinning caster wheel

Structure of the IWOS. The steering joints (green) are actuated, the caster wheel's swivel joint (blue) moves freely. Source: E. Kaltenegger, master's thesis, TU Wien, 2023, Figure 3.2.

Project Scope

• Concept and kinematics: working out how IWOS moves and comparing its maneuverability with conventional differential drive.
• Odometry: an odometer designed for the IWOS kinematics.
• Motion modeling: a stochastic Odometry Motion Model (OMM) that corrects the drift and error that build up in odometry data.
• Prototype: a working IWOS robot built as a proof of concept.

The IWOS prototype robot

The IWOS prototype built during the project. Source: E. Kaltenegger, master's thesis, TU Wien, 2023, Figure 1.1.

Results

Early experiments with the prototype are promising. They suggest that IWOS works as intended and that the OMM improves odometry accuracy. The project lays the groundwork for further development and more detailed evaluation of this locomotion concept.

Master's Thesis

The master's thesis Independent Wheel Offset Steering: Analysis of a Wheeled Robot Locomotion System and an Odometry based Motion Model was written as part of this project. It was submitted by Eugen Kaltenegger to the Faculty of Informatics at TU Wien in 2023 and supervised by Markus Bader.

Related Publication

F. B. Cakar, E. Kaltenegger, G. Todoran, M. Bader. Independent Offset Wheel Steering: An Improved Approach to Wheeled Mobile Robot Locomotion. In Proceedings of the OAGM & ARW Joint Workshop (OAGM & ARW-19), pp. 32–37, Steyr, Austria, May 2019.

Related Patent

TU Wien, M. Bader, G. Todoran. Mobiles System, A 502321/2018 (filed 2018).