Newton’s Cradle is thought of as the most elegant of executive desk toys. But that 20th-century dinosaur just got run off the road as [Ben Katz]’s Furuta pendulum streaks past in the fast lane, flipping the bird and heralding a new king of desk adornments.
This Furata pendulum has wonderfully smooth movement. You can watch it go through its dance in the video after the break. Obviously you agree that this is the desk objet d’art for the modern titan of industry (geek). Just don’t stop at watching it in action. The best part is the build log that [Ben] put together — this project has a little bit of everything!
It’s got the complete rebuild of an electric motor. It’s got machining. There’s electronics. There’s even a guide on control theory. It all comes together so nicely that we can only imagine the lust a Mechanical Engineering professor would have if such an item (just out of his budget’s reach) popped up in a demo aparatus catalog.
A lot happens in the first part of the log. [Ben] is somewhat known for knowing entirely too much (if the metric is how bad he makes us feel about ourselves) about small brushless DC motors. He decided that the off-the-shelf gimbal motor would have entirely too little torque and a practically unsavory amount of cogging. So he rewound the motor coils and machined a completely different housing for it so it could be coreless. Just for good measure he also threw in an encoder which, of course, attaches to his custom motor driver.
Well, a bit more machining, some finishing, and even some of those really nice Lemo connectors later, the mechanical side of the build was done. The second part follows, and dives deep into the motor control and control theory of the device. He starts by tuning his motor driver to work with his newly rebuilt motor. Next he makes his own closed loop controller (which works with a magnet angle sensor from the pendulum). Skirting the standard approach of just bolting a PID library on it and tuning the constants until it looks right as, “not much fun.”