- Keywords: Underactuated Systems, Stabilization Control, Avoiding Null Space
- Abstract: In this retrospective, a high-level principle to guide controller design for underactuated systems based on different treatment on null space will be disclosed, which is inspired by . Firstly, we will show what is avoiding null space in underactuated systems. Secondly, we will introduce how this principle evolves. Thirdly, we will show the tricks that were used in the development. Finally, the limitations in  and corresponding extensions will be presented.