Research Projects

An Omnidirectional Mobile Robot

A mobile robot with four Powered Caster Wheels (PCW) is developed in-house by SIMTech. Mobile robots with Powered Caster Wheels (or "off-centred orientable wheels") have omnidirectional motion capability, that is, having three controllable degrees-of-freedom in planar space. The mobile robot is the composition of the group's competencies in kinematic and dynamic robot modelling, mechanical design, embedded control system, sensors integration and robot motion control. The mobile robot provided a platform for further research in the aspect of mobile robotic as well as mobile manipulator.



The over-constrained feature of the mobile robot makes it important to synchronise the motion between different wheels so as to minimise the effect of slippage. By having more actuation than required to produce the motion (actuation redundancy) of the mobile base, force distribution and slip minimisation algorithms can be implemented to deal with the slippage problem. 

In addition, adopting the methodologies from established automotive vehicle dynamics is a good choice for modelling of the wheel-ground interaction more effectively. This accurate robot dynamic is also critical for applying advanced robust and adaptive observer/controller to the motion system.


  • Autonomous material transportation system (High payload)
  • Autonomous free-ranging surveillance system
  • Omnidirectional manoeuvrability makes it suitable to carry out tasks in cluttered indoor environment
  • Applications which require large workspace manipulation with coordinated obstacle avoidance capabilities (To be implemented with a robot manipulator installed)

Problems Addressed

Conventional caster wheels which are commonly used in office chairs and trolleys offer a number of advantages in terms of payload, traction, simplicity and robustness. A single PCW (with only two controllable degrees-of-freedom) cannot produce an omnidirectional motion. Therefore two or more PCWs are required. However, controlling numerous PCWs to produce a synchronised mobile base motion creates some research challenges such as:

  • Over-constrained kinematics causing slippage
  • Wheel-ground interaction dynamics modelling
  • Non-linear, time-varying, uncertain system control