Supercon: Designing Your Own Diffractive Optics

Kelly Peng is an electrical and optical engineer, and founder of Kura AR. She’s built a fusion reactor, a Raman spectrometer, a DIY structured light camera, a linear particle accelerator, and emotional classifiers for likes and dislikes. In short, we have someone who can do anything, and she came in to talk about one of the dark arts (pun obviously intended): optics.

The entire idea of Kura AR is to build an immersive augmented reality experience, and when it comes to AR glasses, there are two ways of doing it. You could go the Google Glass route and use a small OLED and lenses, but these displays aren’t very bright. Alternatively, you could use a diffractive waveguide, like the Hololens. This is a lot more difficult to manufacture, but the payoff will be a much larger field of view and a much more immersive experience.

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Delta Bot Plucks Out Tunes on a Mandolin

Is there no occupation safe from the scourge of robotic replacement? First it was the automobile assemblers, then fast food workers, and now it’s the — mandolin players?

Probably not, unless [Clayton Darwin]’s mandolin playing pluck-bot has anything to say about it. The pick-wielding delta-ish robot can be seen in action in the video below, plucking out the iconic opening measures of that 70s prom-theme favorite, “Colour My World.” The robot consists of two stepper motors connected to a hinged wooden arm by two pushrods. We had to slow the video down to catch the motion, but it looks like [Clayton] has worked out the kinematics so that the pick can be positioned in front of any of the mandolin’s eight strings. A quick move of the lower stepper then flicks the pick across a string and plucks it. [Clayton] goes into some detail about how he built the motion-control part in an earlier video; he also proves that steppers are better musicians than we’ll ever be with a little “Axel F” break.

It’s only a beginning, of course, but the complexity of the kinematics just goes to show how simple playing an instrument isn’t. Unless, of course, you unleash an endless waterfall of marbles on the problem.

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Smooth Moves from Cheap Motors

Building an electric motor isn’t hard or technically challenging, but these motors have very little in the way of control. A stepper motor is usually employed in applications that need precision, but adding this feature to a motor adds complexity and therefore cost. There is a small $3 stepper motor available, but the downside to this motor is that it’s not exactly the Cadillac of motors, nor was it intended to be. With some coaxing, though, [T-Kuhn] was able to get a lot out of this small, cheap motor.

To test out the motors, [T-Kuhn] built a small robotic arm. He began by programming his own pulse generating algorithm that mimics a sine wave in order to smooth out the movement of the motor. An Arduino isn’t fast enough to do these computations, though, so he upgraded to using the ESP32. He also was able to implement the inverse kinematics on his own. The result of all this work for a specific platform and motor type is a robotic arm that has a very low cost but delivers performance of much more expensive hardware.

The robot arm was built by [T-Kuhn] too, and all of the details on that build, as well as all the schematics and code, are available on the project site if you need a low-cost robot arm or a good stepper motor controller for a low cost. There are many other ways of getting the most out of other types of low-cost motors as well.

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