For 6.131 Power Electronics we get the last month of the class to work on a final project of our choosing. I wanted to work on analog control for balancing an inverted pendulum. The basic idea is that you have a motor with an arm that can rotate. At the end of the arm is a free-hanging pendulum. You use the motor to swing the pendulum. It’s sometimes called a rotary pendulum set-up, sometimes a futura pendulum.
I have the pendulum attached to a d-shaped shaft, which sits in some no-stop potentiometers. The potentiometer gives an analog signal for the angle. The reason I have two is that the no-stop potentiometers have a dead-zone — so I have two back-to-back, one upside down, such that I get signal 360 degrees.
Building the h-bridge to drive the DC motor was the main power electronics part, and to be fair did take me a while to get right. The main key was powering the chips that drive the MOSFETs with a separate power supply than drives the motor, so that when the motor draws a lot of power it doesn’t make the chips enter into a poorly defined state.
Building the analog controller was also really hard! So many op amps. There was a lot of signal processing, and while I have a circuit diagram, it’s missing a couple op amps. I’ll try to fix it and post the complete thing in part two.
I apologize for the confusing circuit board. I put it together pretty haphazardly as I was figuring out what I needed to make it all work.
I also have some video of it kind of working, but that can come in part II.