ROS從”零”開始 – 2. ROSSerial_Arduino測試 (Hello world, 示範publisher)

Posted on by ZanRobot 服務員

就如同各位從零開始的夥伴們，你們一定很想快點看到，一台可以裝上雷射LiDAR導航，自主漫遊 + 路徑規劃 + 自主避障 + 影像AI   &^$%^#%%^%^&%^  ~ 等等集合了目前self-driving 前端科技的家用小車八 !! 我們記錄一位工程師，他是如何從零開始的學習、蛻變到一位 self-driving developer的過程。

話說，這一開始的動作應該也是記錄摸索的過程，不過，這卻是最真實的、殘酷與慘痛代價的經驗。希望這些記錄可以減少後面跟進的學習者們寶貴的時間。

在此定義初階段的學習標的 :

  • 遠端遙控機器人 
  • LiDAR雷達建地圖
  • 自主導航與避障
  • 路徑規劃   (到這 ~ 基本該會的操作都已經具備了)

我們就從 “ROSSerial_Arduino測試 (ROS通訊點亮Arduino LED實驗)” 開始吧 ! 

1-1、Arduino IDE安裝與設定 

 

在解壓縮後的資料夾開啟終端機。輸入：
$sudo sh install.sh

安裝好後，最後會在桌面上看到Arduino的圖案。

1-2、連線架構

使用裝備 : 

  • ACER i5 筆電 win10系統
  • 樹梅派 Pi4 B (2020 年最新版)

測試架構 : 

  • 使用PC (VM)環境架設MASTER 並運行 Publisher 這兩個nodes
  • Arduino 燒錄roserial (ros_lib)的接收程式，控制LED 

筆電中的VM環境再貼一次 :

1-3. 介紹ROS Serial

參考官網 。若是你想用Arduino來做ROS的通訊模組 (也就是作為一個ROS nodes)，包括publish, subscribe ROS的messages， publish TF transforms 和 get the ROS system time。 rosserial provides a ROS communication protocol that works over your Arduino’s UART.  rosserial_arduino package, you can use ROS directly with the Arduino IDE. 喔!  rosserial 這個函式庫下面有許多packages，目的就是在不同硬體系統中，可以容易地運行一個ROS node。

1-4. 安裝軟體

有兩步驟 : 先安裝自己的ROS 工作站 ，再安裝 ros_lib 在自己的Arduino IDE環境中。 

1-4-1.  安裝自己的ROS 工作站 

官網有兩種方式，一個是安裝編譯好的binaries code，另一種是從source code先編譯再安裝，我們選擇第一種(官方建議的)。

You can install rosserial for Arduino by running:

sudo apt-get install ros-melodic-rosserial-arduino
sudo apt-get install ros-melodic-rosserial

你可以把 melodic 換成你自己的ros 版本如 indigo 等

再來到 /libraries 下面檢查是否事先有ros_lib資料夾，若是有先delete掉。

  cd ~/Arduino/libraries
  rm -rf ros_lib
  rosrun rosserial_arduino make_libraries.py .

以上完成後，就可在 /ibraries 下面找到 ros_lib的資料夾

開啟Arduino IDE ，檢查以下是否存在。

arduino_ide_examples_screenshot.png

PS : 目前，另一種更簡單的作法，就是如果你不想花功夫針對你的ROS工作站去做完全安裝，你只是要可以在Arduino上跑ROS的通訊協定，你可以採用以下 : 

*Note: Currently you can install the Arduino libaries directly in the Arduino IDE. Just open the Library Manager from the IDE menu in Sketch -> Include Library -> Manage Library. Then search for “rosserial”. This is useful if you need to work on an Arduino sketch but don’t want to setup a full ROS workstation.

1-5.  測試 Arduino 的 Hello World (example publisher) 

參考官網

先燒錄Arduino程式，第一次可能會出現 ”  can’t open device “/dev/ttyS0″: Permission denied  ” ; 處理方式，

sudo usermod -a -G dialout <username>  , 其中 username 用你Linux的帳號，我自己是 zanrobot ; 完成後先logout出系統，再 login一次。此時，再燒錄Arduino時就不會有問題。

接著當以下 : 

Now, launch the roscore in a new terminal window:

roscore

Next, run the rosserial client application that forwards your Arduino messages to the rest of ROS. Make sure to use the correct serial port:

rosrun rosserial_python serial_node.py /dev/ttyUSB0

此時，又會出現 

[ERROR] [1580567065.273146]: Error opening serial: [Errno 13] could not open port /dev/ttyACM0: [Errno 13] Permission denied: ‘/dev/ttyACM0’

此時，處理一下 serial port權限的問題，

sudo chmod 666 /dev/ttyACM0

測試最後的結果，如下 : 在 VM上的node，可以收到Arduino 發佈出的文字訊息 “hello world” ! 

 

Posted in ROS

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