Experimental 3D Printable Nema 17 Stepper Motor

thingiverse

STEPPER MOTOR: This groundbreaking build is my first attempt at crafting a practical 3D printable stepper motor. The objective was to design a 3D printable stepper motor that could seamlessly replace a Nema 17 stepper motor in a RepRap style 3D printer. This motor has been successfully demonstrated to work directly with a standard Allegro 4988 bipolar stepper driver in the 12 volt range, and boasts a native resolution of 240 steps/revolution in the full-step mode. It runs best, however, in the half-step mode, with an effective resolution of 480 steps/revolution. It features the standard Nema 17 hole pattern for M3 machine screws. The cost was approximately $5USD in parts and took 3.25 hours to print. Motor designed by David Hartkop for the Pueblo City-County Library District's Idea Factory makerspace programming. THE APPROACH: Rather than designing a rotor with high angular resolution, this motor utilizes a single magnet and four electromagnets. The electromagnets are arranged in diagonal pairs, which are wired in series to provide a total of two coil circuits for the motor. The motor has a native resolution of 4 steps per revolution in the full-step mode. This low-resolution stepper motor then drives the input of a split-annulus orbital gearbox, which provides a 60:1 gear reduction. Effort was made to match the impedance of a 0.6W bipolar stepper motor using 33 gage magnet wire. Each of four electromagnets was wound with 75 feet of wire, though exact turns were not considered. RESULTS: This motor functions, but is mostly a curiosity at this point. The torque is suitable for driving a RepRap printer's X or Y stages but the coils were found to easily overheat. I recommend attaching a heat sink to the exposed ends of the four electromagnets. IDEAS FOR IMPROVEMENT: Use steel nuts for iron pole pieces placed around the rotor, gets coils closer to magnet Use large washer or steel square as flux-return over open ends of electromagnets Place heat sink on electromagnets Use looser, lower-friction bearings Use silicone-based lubrication vs. petroleum grease which will degrade the ABS. Use a higher-diameter diametrically polarized magnet for a rotor for better torque. Print Settings Printer Brand: MakerBot Printer: MakerBot Replicator 2X Rafts: Yes Supports: Yes Resolution: Low is fine Infill: 35% Post-Printing Preparing the Printed Gears When first assembled, the gearbox will turn by finger but will be too rough for the low-resolution stepper to turn. The gears require lubrication and wearing in. I found the best way to do this is to first put grease into the gearbox, bolt it closed, and use a cordless drill set to high-speed with an appropriately sized socket to turn the rotor. Clamped the motor block in a vice and clamped the drill into place and essentially wore in the gear box using a high speed drill. Parts: Gears were designed using an open-source JavaScript-based CAD program: http://joostn.github.io/OpenJsCad/ Desired outer dimensions of the motor were found by measuring a Nema 17 stepper motor. Skatboard bearings were found and measured. Bolt sizes for shaft and motor case were decided, holes scaled appropriately. A diametrically polarized tube-type rare earth magnet was found and measured. Planetary arrangement of gears was scaled to fit within desired package size. System designed in Lightwave3D, mesh repair done with Netfabb Basic, and print arrangements made in Makerbot Desktop. Exploded view of the motor Custom Section Video explanation of the inner workings of the 3D printed stepper motor. Sources for this kind of magnet: Be sure to buy magnets that are 'diametric polarization' or polarized 'through width' or 'through diameter'. KJ Magnetics: http://www.kjmagnetics.com/products.asp?cat=16 Magnets4Less: http://www.magnet4less.com/index.php?cPath=13&osCsid=2680da003fca121d7408dfd064084533 MagCraft: http://www.rare-earth-magnets.com/magcraft-nsn0548 Apex Magnets: https://www.apexmagnets.com/magnets/rings