Circles in the sand Spirograph

thingiverse

I'm attempting to create a homemade "Spirograph" in the sand machine. Underneath the board and layer of sand, a magnet moves round in a spirographic pattern. This magnet then pulls a ball bearing round to create tracks in the sand. The magnet is attached inside a gear wheel which is analogous to the ring with holes that you use when drawing a Spirograph. The outer large ring is the same as the geared ring you hold still while drawing the Spirograph pattern. Then, the gear wheel can be turned by driving it with the motor in the center and a pattern produced. To allow for a greater range of patterns, another pair of motors can move the outer ring - this is supported by six wheels that allow it to move smoothly and has tracks on its underside to keep it in position on the wheels. Since the outer ring was too big for my printer, it was printed in four pieces and glued together. By adjusting their relative speeds, different patterns can be produced. As mentioned above, there are two sets of motors - one in the middle and two that run together on the outside. The outer ones drive the large ring - the idea of having two motors here was to ensure it rotated smoothly about its center and didn't come off its tracks. The motors are controlled by a microcontroller through A4988 motor drivers. These are set to run with 16 microsteps, which results in reasonably smooth motion compared to the clunky shaking without microstepping. Cages were produced to hold the motors in position, and everything was screwed to a 360x360x15mm piece of plywood. The gears were drilled with a 5mm drill and tightly fitted on the motor shafts. Originally, an 8mm diameter magnet was glued into the gear wheel. This proved too weak to pull the ball bearing through the sand, although it would pull another smaller magnet under the sand like a mole. Changing to a 12mm magnet solved this issue, but it may now be too strong! Of course, you can use more than one magnet and ball bearing simultaneously. The top board is positioned 60mm above the base. A 3mm thick sheet of plastic was used for the top to hold the sand with a rim to keep it from falling off the edge. Components: * 2 or 3 stepper motors (I used Nema 17 Stepper Motor 1.8° 4-wires 60mm 1.5A 3.52V 0.65N.m) * Arduino/microcontroller * 2* Motor driver (i.e. A4988) * Magnets: + Dia 8mm, *5 mm: 2kg strength + Dia 12mm,*5 mm: 3.6kg strength The Arduino baseplate was taken from here: https://www.thingiverse.com/thing:1816867