This research addresses the issues associated with the components of a smart wheelchair, and develops a navigation system that is retrofitted to a electric powered wheelchair. The navigation system takes a systems engineering approach, integrating many existing open-source software projects. It is aimed at operation in an unstructured indoor environment, and requires no a priori information about the environment. The key components in the system are: obstacle avoidance, map building, localisation, path planning, and autonomously travelling towards a goal. The test electric wheelchair is instrumented with the following: a laptop, a laser scanner, wheel encoders, camera, and a variety of user input methods. The user interfaces include: a touch screen friendly graphical user interface, keyboard, joystick, and basic speech control.