These feet have slots under the washers so that the tension of the GT2 belt could be adjusted. Two parts attach directly to the motor and the other four parts are the feet, which attach to the base. The stand for the inverted stepper motor is made of 6 separate parts, due to the constraints of 3D printing parts with overhangs. The base had four holes in the corners to bolt it to the bottom of the enclosure. The lower portion (shown with the main rotation shaft installed above, and an Arduino for testing purposes) served to mount the motion assembly to the inside of the case and rotate the rail above it. With the use of conductive tape, spring tensioners, and 3D printed parts, it transfers electricity to the four wires of the rail stepper motor while allowing the rotor to make an endless number of rotations without getting twisted in wires. The connection point between these two points, which I’ll call the main rotation shaft, was one of my favorite challenges of the build. There’s also a bunch of random metric bolts, nuts, and washers (mostly M3) as well as some miscellaneous circuitry and wires. In addition to the hardware mentioned above, which were mostly ordered off Amazon, the white parts were designed in Fusion 360 and 3D printed on my Prusa MK3s with PLA filament. It included a metal linear rail with shuttle, GT2 timing belt, idler pulleys, and a NEMA 11 bipolar stepper motor with a 16 tooth pulley on the shaft. The rail is the part being spun around by the rotor and determines the radial position of the magnet. The mechanical portion of the project can be considered in two parts that had to work together, which I ended up calling the “ rotor” and the “ rail.” The rotor is the part that spins the assembly around in circles and included a NEMA 17 bipolar stepper motor, GT2 belt, a 16 tooth and 60 pulley (smaller on the motor shaft, large on the main shaft), an 8mm diameter metal rod (main shaft), and a pillow block bearing. Later in my project, after adding sand, I found that the 20mm spherical magnet tried to ride above the sand more than plow through it, so I replaced it with a much smaller 5mm spherical magnet (like the ones that were a popular toy a few years back, until a bunch of kids ate them and got sent to the hospital for kinking up their insides). Testing this combination by moving the magnets with my hands left me confident they would work. These would be separated by 3mm frosted acrylic, which I could cut on a laser cutter. I initially settled on a cylindrical neodymium magnet for underneath (10mm in diameter and 3mm tall) paired with a 20mm spherical magnet for the top. I also did plenty of tests with potential materials for the table top, since I didn’t want to get too far along, only to find my table surface was too thick to keep a strong magnetic attraction between the upper and lower magnets. Next, I experimented with different combinations of magnets to find ones that were strong and small. Because it’s always nicer to have a wireless final project, I decided to go with the former.įor motion, I knew I’d be working with stepper motors, so I ordered a few variations to experiment with and some motor controllers. I decided I would either use a RaspberryPi, or have an Arduino directly connected to an operating computer. I knew the complexity of these movements would be more than a microcontroller alone could do, at least for more than the most basic shapes. Initial Decisions ElectronicsĪs is clear to most people, the whole operation hinges of being able to move a magnet around in a complex pattern under a table covered with fine sand. I love troubleshooting problems, so don’t hesitate to reach out to me if you have any questions. I’ve tried to provide enough insights, diagrams, pictures, code, and “lessons learned” that a motivated maker would be able to recreate my project, but still with some enjoyable challenges along the way. As an up front disclaimer, this is not a step-by-step “how to” tutorial.
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