Pick-and-place robot arm (2 servos)

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from gpiozero import AngularServo, Button
from time import sleep

base = AngularServo(17, min_angle=-90, max_angle=90)       # turns left and right
grip = AngularServo(18, min_angle=-90, max_angle=90)       # 60 = open, -20 = closed
start = Button(27)

def move(base_angle, grip_angle, text):
    print(text)
    base.angle = base_angle
    grip.angle = grip_angle
    sleep(1)

move(0, 60, "Home position, gripper open")

while True:
    start.wait_for_press()
    move(-60, 60, "1. Swing over the part")
    move(-60, -20, "2. Close the gripper: part picked")
    move(60, -20, "3. Swing to the drop point")
    move(60, 60, "4. Open the gripper: part placed")
    move(0, 60, "5. Back home. Ready")

How the code works

• move() sets both servo angles and then waits one second for the arm to get there.
• Each call to move() is one pose. The cycle is five poses in order.
• wait_for_press() pauses the program until the button is pressed, so the cycle runs once per press.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.