Sand drawing

Huh?

So you've been reading about all the benefits of this "mindfulness" thing and you want to give it a try. You do some research and learn it requires "meditation", "introspection" and other kinds of tedious woo. Who has time for that? It's {current_year} for christ's sake! I don't want a tiny tray of rocks and sand on my desk to rake around. Surely there's some turn-key solution to this problem already.

That's what this project is for. Outsource responsibility for an ordered mind to make more time for the important things, like computer games. And croissants.

Oh

This project (will contain/contains) all the knowledge you will need to build your own sand drawing robot. Heavily inspired by the likes of Sandsara and Sisyphus. It's a robot that moves a ball around in a bed of sand to draw cool patterns. The patterns can be updated via wifi, and it can cycle through them, you can create your own, etc, etc. This project is open source, cheap, and hopefully as easy as possible to build.

Building it

Skills required

This isn't a Lego set. You'll need to have access to the following skills:

• Basic woodworking,
• Intermediate soldering,
• Following technical instructions,
• Drilling a hole sideways through steel rod,
• Recovering from setbacks.

I'll do my best to make the instructions as comprehensive and comphrehensible as I can. I appreciate any and all feedback.

Videos

Playlist on Youtube. Maybe worth watching.

PCB

The PCB is quite simple and cheap. PCBWay generously sponsored a production run of the v1.2 PCBs and they came out perfect. You can order the PCB using this link and I'll get a small cut. PCBWay asked me to review the board in a youtube video and link it in the readme, but required no further quid pro quo.

Build logs

For now the build logs are on my wiki. Over time they'll morph into actual instructions and end up in this repo.

Bill of materials

None of these parts are particularly hard to find. Check ebay and whatnot. Try to buy local if you can. It's hard to guess how much it will all cost in total, but I've tried to design everything to be as economical as possible. Excluding the housing I would (very roughly) estimate the BoM to come out to around AUD$200. The housing could be as cheap as AUD$50 (Melamine board, polycarbonate) or as expensive as you want, with lacquered hardwood and tempered glass.

These bills of material are slightly out of date. Consult the youtube videos.

Mechanical

Electrical

Enclosure

Flashing

To flash the software onto the ESP32 you'll need to use the provided scripts flash32.sh and write32.sh. You'll have to update them with the current version of micropython and the device name of your serial port adapter. When flashing micropython you'll need to hold down the IO0 button while connecting power, then release it five or so seconds after powering on. You can then run flash32.sh and it'll write the "OS" onto the chip. Then you can repower again and run write32.sh to load the project's scripts onto the board.

Communication

The ESP-WROOM-32 has wifi and BLE built in. Currently the robot connects to a wifi network, then an MQTT server, to receive commands. Bluetooth should also be possible in the future.

MQTT Topics

There are a few topics that the robot listens to. Each topic starts with {secrets.mqtt_root}/sand_drawing/. I suggest you publish patterns/generators with the retain bit so the robot starts up and then begins that pattern.

Configuration

There are some files you'll need to edit before your robot will work for you, probably. #TODO populate this section.

Pattern definition

There are currently two ways to design patterns for the robot.

GCODEs

This is a sequence of coordinates that define the path of the ball, as well as changing modes and looping. The following GCODES are currently supported. GCODES are separated by a comma.

Generators

You can define a pattern using a python generator function. Examples here. This is probably the best option for non-trivial patterns.

Tread lightly

Keep the target hardware in mind when writing generators. It's very resource-constrained. Try to limit RAM usage, and think hard before importing anything. There are some helper functions and constants in-scope that you can use.