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Inverted Pendulum

An Inverted Pendulum is a mobile whose pivot point is below its center of mass. A pendulum is perfectly stable when hanged downwards. However, its inverted counterpart lays upside down and is inherently unstable. As a result it must be actively balanced in order to maintain its equilibrium in its unnatural position. This is a classic problem in dynamics and control theory.

There are many variations of inverted pendulum and YouTube should be able to give you an idea of this. An example is the two wheeled platform and the Segway is maybe the most emblematic application since, in addition to being surprising, it has also useful and practical. Some inverted pendulum are made of a car ranging a rod while others maintain equilibrium of a segmented rod attached to a rotation assembly. Another impressive inverted pendulum is even a flying quadricopter ranging a rod on the top of its back.

Inverted Pendulum assembly

The pendulum proposed here is a reaction wheel inverted pendulum. It is based on the conservation of angular momentum through the proper control of a reaction wheel. It uses the same principle as attitude control in spacecraft. As you can see it in the picture, the contact point between the pendulum and the ground is simply an edge of the casing. The pendulum can still balance around this edge by driving the wheel attached to its motor. You can check out the performances of this pendulum on the video below. As you can see, the pendulum is even capable to jump from its rest position.

In addition to its originality, the main advantages of this project are that this pendulum is relatively small and is completely self-contained. It can run several hours thanks to its internal Lipo battery.

This project is freely inspired from the Cubli project from ETH Zurich. Being 1D, it is much more simpler that the Cubli but the basic principle remains the same. It is an ideal mobile for students wishing to study modern regulation.