Raspberry Pi Zero Dynamixel Hat

Raspberry Pi Zero Dynamixel Hat

The Dynamixel Hat is a board capable of communicating the raspberry Pi ( Serial ) with the Dynamixel servos by using the 74LS241 Tri-state Buffer connected to 3-pin Molex connectors.

The board contains a TI TPS62143 regulator that steps down the voltage to power up the Raspberry Pi Zero that can be power on or off with the onboard slide switch. The TPS62143 is a synchronous step-down DC-DC converter optimized for applications with high power density.

This board accepts 2S and 3S Lipo batteries, the DC-DC converter accepts up to 17 Volts but the motors recommended voltage is 11.1V ( 3S Lipo ) as the MAX Input voltage is around 16 Volts.

The boards incorporate two I2C ports for sensors for your robotic project. These are JST 1 mm pitch and 4-pin connectors compatible with many boards on the QWIIC family.

There are also 3 LEDs and 3 Buttons for notification and interaction with the electronics, the buttons are programable through the Raspberry GPIOs and 1 LED also GPIO Configurable, the other 2 LEDs are the Activity and PowerOn notification.

Assembly Video

PINOUT

Test code (Python):

import RPi.GPIO as GPIO
import serial
import time

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(18,GPIO.OUT)     # Control Data Direction Pin
GPIO.setup(6,GPIO.OUT)      # Blue LED Pin

GPIO.setup(26,GPIO.IN)      # S2 Push Button Pin
GPIO.setup(19,GPIO.IN)      # S3 Push Button Pin
GPIO.setup(13,GPIO.IN)      # S4 Push Button Pin


Dynamixel=serial.Serial("/dev/ttyS0",baudrate=1000000,timeout=0.1, bytesize=8)   # UART in ttyS0 @ 1Mbps


while True:

    if GPIO.input(26):
        GPIO.output(6,GPIO.LOW)
    else:
        GPIO.output(6,GPIO.HIGH)
        GPIO.output(18,GPIO.HIGH)
        Dynamixel.write(bytearray.fromhex("FF FF 01 05 03 1E CD 00 0B"))  # Move Servo with ID = 1 to position 205
        GPIO.output(18,GPIO.LOW)
        startDynamixel = Dynamixel.read()
        startDynamixel = Dynamixel.read()
        idDynamixel = Dynamixel.read()
        lenghtDynamixel = Dynamixel.read()
        errorDynamixel = Dynamixel.read()
        chkDynamixel = Dynamixel.read()
        print("Servo ID = " , int.from_bytes(idDynamixel,byteorder='big') , " Errors = ", int.from_bytes(errorDynamixel,byteorder='big'))
        time.sleep(1)

    if GPIO.input(19):
        GPIO.output(6,GPIO.LOW)
    else:
        GPIO.output(6,GPIO.HIGH)
        GPIO.output(18,GPIO.HIGH)
        Dynamixel.write(bytearray.fromhex("FF FF 01 04 02 2A 01 CD"))   # Read Voltage of Servo with ID = 1 
        GPIO.output(18,GPIO.LOW)
        startDynamixel = Dynamixel.read()
        startDynamixel = Dynamixel.read()
        idDynamixel = Dynamixel.read()
        lenghtDynamixel = Dynamixel.read()
        errorDynamixel = Dynamixel.read()
        voltDynamixel = Dynamixel.read()
        chkDynamixel = Dynamixel.read()
        print("Servo Voltage = " , int.from_bytes(voltDynamixel,byteorder='big'))
        GPIO.output(18,GPIO.HIGH)
        Dynamixel.write(bytearray.fromhex("FF FF 01 04 02 2B 01 CC"))   # Read Temperature of Servo with ID = 1
        GPIO.output(18,GPIO.LOW)
        startDynamixel = Dynamixel.read()
        startDynamixel = Dynamixel.read()
        idDynamixel = Dynamixel.read()
        lenghtDynamixel = Dynamixel.read()
        errorDynamixel = Dynamixel.read()
        tempDynamixel = Dynamixel.read()
        chkDynamixel = Dynamixel.read()
        print("Servo Temperature = " , int.from_bytes(tempDynamixel,byteorder='big'))
        GPIO.output(18,GPIO.HIGH)
        Dynamixel.write(bytearray.fromhex("FF FF 01 04 02 24 02 D2"))   # Read Position of Servo with ID = 1
        GPIO.output(18,GPIO.LOW)
        startDynamixel = Dynamixel.read()
        startDynamixel = Dynamixel.read()
        idDynamixel = Dynamixel.read()
        lenghtDynamixel = Dynamixel.read()
        errorDynamixel = Dynamixel.read()
        posDynamixel = Dynamixel.read(2)
        chkDynamixel = Dynamixel.read()
        print("Servo Position = " , int.from_bytes(posDynamixel,byteorder='little'))
        time.sleep(1)

    if GPIO.input(13):
        GPIO.output(6,GPIO.LOW)
    else:
        GPIO.output(6,GPIO.HIGH)
        GPIO.output(18,GPIO.HIGH)
        Dynamixel.write(bytearray.fromhex("FF FF 01 05 03 1E 32 03 A3"))    # Move Servo with ID = 1 to position 816
        GPIO.output(18,GPIO.LOW)
        startDynamixel = Dynamixel.read()
        startDynamixel = Dynamixel.read()
        idDynamixel = Dynamixel.read()
        lenghtDynamixel = Dynamixel.read()
        errorDynamixel = Dynamixel.read()
        chkDynamixel = Dynamixel.read()
        print("Servo ID = " , int.from_bytes(idDynamixel,byteorder='big') , " Errors = ", int.from_bytes(errorDynamixel,byteorder='big'))
        time.sleep(1)

Enable UART at 1Mbps in your Raspberry Pi Zero

Make sure to add the following to your Raspberry config file at /boot/config.txt:

enable_uart=1
init_uart_clock=16000000

Why did I make it?

A lot of people are using the Dynamixel Servos for robotics projects and the Raspberry for high the controller, and have been asking me to re-stock the board as they want to use these awesome motors but don't want to mess up with the electronics part and that's why I decided to produce a small batch with the feedback of this awesome robotics community.

What makes it special?

It implements the Savage Electronics Dynamixel Interface. Power is provided directly from a battery to the motors and the Raspberry Pi Zero. Easy to install.

This board is available in my Tindie store: Savage Electronics Tindie