3. Wire up the plotter

Important

Make sure the Raspberry Pi is turned off while you’re wiring it up.

Although the Raspberry Pis can take a frankly amazing amount of abuse, you run the risk of causing damage if you get the wiring wrong. Do it with the power off, take your time, and double-check your work.

The three servos need to be connected to the Raspberry Pi. Each servo has three wires:

  • 5V (power)

  • Ground

  • Signal

5V and ground are required to power the servo; the signal wire carries a pulse, whose width (its length in microseconds) determines the position of the motor.

At least two of the servos will need to share a 5V connection, since the Raspberry Pi has only two available. How you achieve this will depend on what you have available.

If you have a breadboard, you can wire the servos up so:

I prefer to solder a little wiring loom out of jumper cables, that the servo’s leads connect to, so that they all share a single connector for 5V, and a single connector for Ground. That way, you can use just 5 pins on the Raspberry Pi, all next to each other. It looks like this:

This connects to the Raspberry Pi like so:

3.1. Check the connections

Double-check each connection all the way from the servo to the Raspberry Pi.

servo lead

GPIO pin

physical pin

all 5V leads

any 5V power pin

2 or 4

all Ground leads

any Ground pin

6, 9, 14, 20, 25, 30, 34, 36, 39

shoulder motor signal

14

8

elbow motor signal

15

10

lifting motor signal

18

12

Note

https://pinout.xyz has some useful information about the pins.