This Table Automatically Draws Mesmerizing Patterns and Shapes in the Sand
Roberto Groza's table moves a ball bearing to draw fun and creative designs while also providing RGB lighting effects.
Traditional zen gardens normally feature some form of rock bed that can be raked into a pattern. This can be very relaxing, but it also requires a lot of time and skill to create something that looks aesthetically pleasing. That's why Instructables user Roberto Groza created this miniature sand table that is able to automatically redraw its design to nearly anything with ease. But that's not all. There is also a ring of RGB LEDs on the inside that can illuminate the design in interesting ways to give another layer to the design.
Hardware and Electronics
The brain of this project is a Raspberry Pi, and it controls everything from the stepper motors to the RGB LED strip. The table rotates by turning a single NEMA17 stepper motor, and the second axis (horizontal slide) is moved along a track with another NEMA17 motor. They are driven by a pair of DRV8825 stepper motor driver modules that can be controlled with only two wires. There is also an LCD that gives information about what design is currently being drawn and how much progress has taken place so far.
The table itself is constructed from a simple 1/2" sheet of plywood and a 31" diameter piece of circular tempered glass.
Slide and Rotational Mechanisms
The table works by moving a small metallic bearing around a bed of sand with a magnet to draw various patterns. It can move in two axes: rotate around the Z axis and in a linear X axis. The sliding mechanism rests just below the bottom of the display case, and it holds the sliding armature containing the magnet. The entire assembly is built upon a V-slot aluminum extrusion and is driven by a belt connected to a stepper motor's pulley.
For the rotating portion, there is a central pipe mounted inside of a bearing that allows it to rotate smoothly around. To ensure the stepper motor can apply adequate torque, there is a large drive gear around the entire shaft to give extra leverage. At the end of each axis, there is a limit switch that activates when a bumper hits it, thus providing a homing mechanism.
Designing and Fabricating the Table
The table's wooden components were designed in Fusion 360, laid flat onto a single plane, and then cut with a laser cutter. This gives each piece extra strength to hold up the heavy glass piece. The legs flair out from underneath the table's bottom to form a cone shape, giving more rigidity.
The glass piece rests on top of a small ledge that is created by inlaying a piece of plywood that has an inner diameter that is slightly smaller than the outer piece. This gives a nice transition between the glass and the wooden frame without needing to use some kind of ugly bracing or glue to hold it in place.
The Program
The program that the Raspberry Pi runs is quite similar to any standard gcode firmware. A selected gcode file is loaded and then executed, with each line containing the positions and timings for both axes. It begins by calibrating each axis by moving the slider and table top until each limit switch is hit. Then the user can select a pattern to draw from the LCD.