SPLOTCH is a parallel arm SCARA plotter, that can usually trick people into thinking it draws what it's meaning to.

This project was built in 72 hours as part of the Undercity Hackathon in SF, and it's state does represent that.

https://youtu.be/LqYqyEfOcu8

Going into this, I had literally no idea how to make a robot arm, and here I am now, with still almost no idea how to make a robot arm. Anyways, we made this. We started by researching different mechanisms, we settled on this because it didn't need a belt, and kept the arms relatively light. Servos were used for their relative ease of use over steppers, and the fact they didn't need dedicated driver boards which were in very short supply. The first versions of the arm assembly were designed to not require screws, but the relative unreliability of PLA lead to a lot of broken parts, and thus the decisiion to screw literally everything together. ( exept for the pen holder, which was most efficient to do snap fit )

Considering the relatively lightweight requirements, you can build your own SCARA plotter with a few servos, some 3d printed parts, and a pen. Specifically, you will need:

1. Print all 3D parts, or get some elsewhere.

2. put the servos in the holder, and fix them in place with double sided tape or glue.

3. Attach the holder to the baseplate, in the center of the bottom edge. The curved corners of the baseplate should be facing forwards, and the wires of the servos should be facing backwards.

4. Attach the front and back links of each arm. The m.2 screw should pass through the first arm and bore into the second arm, securing them together and allowing room for rotation. The screws on the two front arms will face opposite directions, and the screws on the two back arms will face opposite directions. The front arm should be on the top, and the back arm should be on the bottom.

   

5. Attach the third servo to the end of the arm, in the small slot.

6. Wire up the motors, and rotary encoders, referencing this wiring diagram:

8. attach the breadboard and servo holder to the baseplate
9. Place the case over the breadboard, make sure to reconnect wires properly
10. Insert rotary encoders into the slots on the lid (maybe use glue), slide in the lid.
11. Done!

1. Connect the Raspberry Pi Pico to your computer via USB.
2. Setup python enviroment by running:

pip install -r requirements.txt

3. Flash the firmware to the Pico by running:

mpremote connect auto fs cp firmware/main.py :

4. use minicom or any other serial terminal to connect to the Pico:

minicom -D /dev/tty.usbmodem1101 -b 115200

5. Once connected, you can send commands to the plotter, you can use the following commands:
   • angle_a,angle_b - Move to servo angles (e.g. 120,60)
   • xy:x,y - Move to XY coordinates (e.g. xy:50,80)
   • pen:up, pen:down or pen:dot - Move pen up or down, or do both (down-up)
   • safe:x,y,w,h - Set safe zone (paper) parameters (e.g. safe:-50,100,100,100)
   • safe:on or safe:off - Enable or disable safe zone checks
   • enc:on or enc:off - Enable or disable encoder (manual) control")
   • enc:step:N - Set encoder sensitivity (N = degrees per step, e.g. enc:step:0.5
   • exit - Quit program Command can be chained together with a semicolon, e.g. angle_a,angle_b;xy:x,y;pen:up
6. To generate complex strings of commands, you can either use visualizeIK.py to draw your own, or use the SVG to commands script to convert an SVG file into a set of commands.
7. • Use ik_path_planner.py to draw your own commands:
   • Run python3 firmware/ik_path_planner.py
   • Click on the canvas to add a point, adding subsequent points will create a line between them. To raise the head, click the "Pen Up" button, and to lower it, click the "Pen Down" button. to create a dot at your current position, click the "Pen Dot" button.
   • Once you are done, click the "Generate Commands" button to generate a set of commands based on the points you have drawn.
   • The generated commands will be printed to the console.
   • Copy the commands to your clipboard and paste them into the serial terminal to see them executed.