https://wiki.tjhowse.com/ 2026-04-17T15:07:36+00:00 https://wiki.tjhowse.com/ https://wiki.tjhowse.com/_media/wiki:logo.png text/html 2020-04-17T05:11:26+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:cad What I want to accomplish * Design the 3d printed parts, * Print them, * Assemble everything. What I've done I broke out my favourite CAD tool: OpenSCAD and wrote a bunch of code. I found an openscad library on Thingiverse that can generate GT2 pulleys. My belts aren't quite GT2, but they're close enough. text/html 2022-01-23T00:25:43+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:design_and_scrounge What I want to accomplish * Work out how Sandsara works, * Scrounge the bits I need. What I've done The Sandsara Kickstarter page has a nice little gif showing the internal workings of the mechanism. Here's a still from that gif: Here we can see the two arms, driven by two stepper motors. The bottom stepper drives the first arm, the top stepper drives the second arm. The first arm seems to be fixed to the first axis shaft, and the shaft is driven by a belt-driven pulley connected to th… text/html 2020-04-17T05:11:45+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:electronics What I want to accomplish * Do the electronics What I've done I'm using some old Pololu A4983 stepper drivers for prototyping. They're fairly rubbish, die often, and can be noisy. I've got some newer DRV8825 modules on the way. They're pin-compatible, so I should be able to upgrade without much hassle. text/html 2020-06-04T00:36:11+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:even_mode_software What I want to accomplish * Cooler patterns. What I've done Cooler patterns I wrote a helper script to generate GCODE for some a cool pattern. It draws around the circumference of the bed and then spirals into the centre, then spirals back out to the edge again. I thought it would be very cool. I incorporated the MQTT GCODE publication into the generation script so it was a one-step test process. text/html 2020-04-17T05:11:04+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:final What I want to accomplish * Document what I would've done differently. What I would've done differently Use mild steel shafts everywhere, not stainless. It's much easier to cross-drill. Consider alternate arrangements of steppers: Make a coffee-table sized version. text/html 2020-05-26T12:24:32+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:further_electronics What I want to accomplish * Design the PCB What I've done Microcontroller I went back and forth on this a few times. There were two main choices to make: * ESP8266, or * ESP32 and * Breakout board, or * Implement directly. In my first text/html 2020-05-11T11:29:34+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:further_improvements What I want to accomplish * Improve the mechanical design What I've done I've made a few more improvements since improvements. * Added optoswitches for zeroing axes, * Tabs on arm1 and arm2 to pass through the optos, * An arm to hold the optos. text/html 2020-05-13T13:15:22+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:further_software What I want to accomplish * Do the inverse kinematics, * Check the bounds, * Improve the kinematics. What I've done Inverse kinematics This is a fancy term for “calculating the joint angles required to achieve a given tool position”. In our case the tool is the ball. I found a good guide to the maths at text/html 2020-05-12T09:21:53+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:improvements What I want to accomplish * Improve the mechanical design What I've done I've made a few improvements since Work Log: CAD. Optoswitch mounts In order to test the software before finishing the complete enclosure I needed a way to mount the optoswitches roughly where they'd be in the final product. I need the optoswitches to detect the position of the arms. Stepper motors have no positional feedback of their own, so the usual system is to move them until you detect them in a certain positio… text/html 2020-04-23T22:54:00+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.tjhowse.com/projects:sand_drawing:work_logs:software What I want to accomplish * Write the software. What I've done The software needs to do a few things: * Connect to my MQTT server for control purposes, * Receive new patterns, * Trigger patterns. * Do the kinematic calculations, *