The circular wheel has been used throughout human history and demonstrated its efficiency. However, even though the wheel has evolved over a long time, off-road driving performance and obstacle-overcoming capabilities are still not sufficient for the small wheels that could be used for mobile robotic platforms. Those robotic vehicles with a special perforce should limit their size as well as the size of the wheel, consequently, the dimension of the wheel is also limited.
In this research, an expandable wheel with a star-shaped spoke, which can expand its diameter without changing thickness, and an actuation mechanism for the expandable wheel is designed. The expandable wheel is equipped with a telescopic structure that could extend its length without changing other dimensions and can have a long stroke compared to its own length by assembling multiple spoke units. Additionally, a root structure that is attached to the individual spoke units was designed to reinforce the spoke assembly was designed and synchronize mechanism that prevents the spokes units move freely and limits the stroke range of the spoke assembly was also applied. The expandable wheel showed that it could expand its diameter more than two times and bear the load without shrinking its diameter. The wheel was equipped with a mobile platform and showed the capability could go through several terrains such as on-road, off-road, and high obstacles.