Circles in the sand Spirograph

thingiverse

This is my attempt to make a 'Spirographs' in the sand machine. Under 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 glued inside a gear wheel which is analogous to the ring with the holes in you use when you draw 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 then be turned by driving it by the motor in the center and a pattern produced. To allow a greater range of patterns the a second pair of motors can move the outer ring - this is supported by 6 wheels which allow it to move smoothly and it has tracks on its underside keep it in position on the wheels. Since the outer ring was too big for my printer it was printed in 4 pieces and glued together. By adjusting their relative speeds different patterns can be produced. As mentioned above has two sets of motors - one in the middle and 2 which run together on the out side. The outer ones drive the large ring - the idea of having 2 motors here was to ensure it rotated smooth about its centre and didn't come off its tracks. The motors are controlled by a micro controlled through A4988 motor drivers. These are set to run with 16 microsteps, this results in resonably smooth motion as compared with the clunky shaking with no micro stepping. Cages were produced to hold the motors in position and everything screwed to a 360*360*15mm peice of plywood. The gears were drilled with a 5mm drill and tightly fitted on the motor shafts. Originally an 8 mm dia magnet was glued in the gear wheel. This proved to weak to pull the ball bearing through the sand, although it would pull another smaller magnet under the sand like a mole. Changing to 12mm magnet solved this, although it may now be too strong! Of course you can use more than 1 magnet / ball bearing simultaneously. The top board is positioned 60mm above the base. I 3mm thick sheet of plastic was used for the top to hold the sand with a rim to keep it from falling of 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 / micro controller 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