A Low-cost and Flexible Open-source Inverted Pendulum for Feedback Control Laboratory Courses

This paper presents the complete design and build o f a low-cost, open source inverted pendulum (IP) platform to support control systems engineerin g a d technology laboratory instruction. In this standard IP system, a linear actuator consisti g of a belt drive and stepper motor is used to stabilize the vertical angular position of an inver ted pendulum connected to a cart. The novelty of the presented system is the open-source approach, w hich achieves both low-cost and permits individual customization. The linear actuator and c art were designed in SolidWorks and manufactured using a MakerBot Replicator 2X, with t he design files published on ThingiVerse.com. Linear motion is achieved via a st andard NEMA17 size stepper motor driven by an Arduino Uno microcontroller development platf orm and an open source stepper motor driver circuit that can either be purchased or buil t in-house. Angle conversion of the IP is performed using a low cost rotary encoder and the a nalog to digital convertor of the Arduino Uno. Additionally, a digital Proportional Integral Derivative control algorithm is presented that addresses the issues of sample time, derivative kic k, on-the-fly tuning and reset windup. The code is documented to explain these phenomenon and to enable tuning using standard practices such as Ziegler-Nichols tuning. Through the use of 3D printing technology and open-source electronics and computer code, the material cost of the system was kept under $100 per unit, making this an ideal student project for an undergr aduate controls curriculum. Additionally, through open access to the design files, control sy stems educators and students have the flexibility to customize the project to their indiv idual needs. Student feedback is also presented supporting the efficacy of the system as an active learning tool.