Work in progress. Inspired by https://openmower.de/
- Lawn Mower: ZSA Zuchetti Ambrogio L15 Deluxe
- Computer: Raspberry Pi 4 (8GB)
- Microcontroller: Arduino Nano
- Motor drivers: ZS-X11H V2
- GPS Devices: Ardusimple Simplertk2b
- IMU: BNO055
- Battery: Einhell 18V 4Ah LI-ION Battery Pack
- Voltage Convertor: KIS3R33S DC-DC 7-24V to 5V USB Step-Down
- Some resistors (1 kOhm, 4.7 kOhm), transistors (2N2222) and cables
- Ubuntu 20.04 Server
- ROS1
- Installed Packages:
git unzip ros-noetic-ros-base python3-pip rtklib build-essential ros-noetic-controller-manager ros-noetic-joint-state-controller ros-noetic-serial ros-noetic-robot-state-publisher ros-noetic-xacro ros-noetic-diff-drive-controller ros-noetic-teleop-twist-keyboard i2c-tools ros-noetic-ublox ros-noetic-gps-common ros-noetic-robot-localization ros-noetic-move-base
To ensure that we have constant device names that we can use to access the different devices over USB, we create some udev rules. First we plugin the different devices one by one and identify vendor and product IDs for each of them by typing lsusb in between:
...
Bus 001 Device 007: ID 0403:6015 Future Technology Devices International, Ltd Bridge(I2C/SPI/UART/FIFO)
Bus 001 Device 008: ID 1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter
...
Then we can create a rule file sudo vi /etc/udev/rules.d/91-usbdevices.rules with the following content (adjust your idVendor and idProduct if necessary):
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", SYMLINK+="usb-ardusimple"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="7523", SYMLINK+="usb-nano"
Have the rules applied by typing sudo udevadm trigger and then check that the symlinks were actually created by issuing ls -l /dev/ttyUSB* /dev/usb-*:
crw-rw---- 1 root dialout 188, 0 Apr 2 07:07 /dev/ttyUSB0
crw-rw---- 1 root dialout 188, 1 Apr 2 07:07 /dev/ttyUSB1
lrwxrwxrwx 1 root root 7 Apr 2 07:07 /dev/usb-ardusimple -> ttyUSB0
lrwxrwxrwx 1 root root 7 Apr 2 07:07 /dev/usb-nano -> ttyUSB1
We are using some cheap ZS-X11H V2 motor drivers to interact with the BLDC motors from the mower. The HAL encoders need to be pulled up high for the motor driver to be able to read the position values. Refer to this guide to get more information. I used 4.7 kOhm resistors. The direction has to be controlled by connecting a pin to ground. As this cannot be achieved with an Arduino out of the box, I used a 2N2222 transistor and a 1 kOhm resistor as suggested in this forum entry.
If you live close enough to a reliable publicly available base station, you don't necessarily need to do run your own GPS base station.
But for our setup we are going to install one ourselves. The Simplertk2B is transmitting its data to the free NTRIP Caster rtk2go.com so it can not only be used by myself but also by others that live close enough. You can use any ESP32 and flash it with the same firmware that Ardusimple is also using for their WiFi NTRIP Master ESP32.
If you want to achieve sub-centimeter accuracy also for absolute positions you can use one of the free PPP services for post processing your exact location. For this you first upload the RAW data (PPK) over UART1 & USB at 1Hz configuration from Ardusimple's provided configuration files. You start up u-center and record raw data to a file for 24 hours. Then you convert the .ubx file to a RINEX .obs file and upload it to Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP). You will then receive a report with the very precise position of your base station's antenna. You can now upload the Base configuration from Ardusimple's provided configuration files and then adjust the survey in method from survey in to fixed in u-center under UBX->CFG->TMODE3 together with your precise coordinates. Don't forget to persist your changes under UBX->CFG->CFG. There's a great tutorial from Sparkfun that helped me a lot. The F9P configuration (with my specific location) can be found in gnss-base.txt.
The Simplertk2b is going to be connected to the Raspberry Pi through a serial connection (using the provided Arduino Serial Shield by Ardusimple). For this to work, serial needs to be enabled by adding the line enable_uart=1 to /boot/firmware/syscfg.txt. As we don't want to login through serial we remove the part console=serial0,115200 from /boot/firmware/cmdline.txt. Disable serial Getty by sudo systemctl stop serial-getty@ttyS0.service and sudo systemctl disable serial-getty@ttyS0.service.
Furthermore Bluetooth needs to be disabled. This can be done by adding another line dtoverlay=disable-bt to the file /boot/firmware/usercfg.txt.
Unfortuunately, as soon as the Simplertk2b is connected, the Pi will no longer boot. When hooking it up to a screen through HDMI you see that it is stuck before booting into Ubuntu. This is because the messages from the GPS module coming through serial now interrupt the autoboot countdown. Therefore we don't want to use u-boot anymore for bootloader but start into Ubuntu directly. As suggested in Ubuntu's wiki for the Raspberry Pi we do so by commenting out the device_tree_address section in /boot/firmware/config.txt and by exchanging the line kernel=uboot_rpi_4.bin for kernel=vmlinuz and by adding the line initramfs initrd.img followkernel just below.
After rebooting you should now see (scrambled because of binary UBX protocol) messages coming in from the GPS device when you look at less -f /dev/ttyAMA0.
The connection is done from the Raspberry Pi through USB to the second USB port of the Simplertk2b board that connects to the XBee socket, where we connect the RX/TX-pins according to this guide on Youtube. Additionally, the Baudrate for UART1 is also increased to 115200 in u-center under UBX->CFG->PRT. The F9P configuration can be found in gnss-rover.txt.
For sending the correction data, we use str2str, which doesn't have to be compiled ourselves but can simply be installed as an Ubuntu package with sudo apt install rtklib. As we want to have the data streamed to the Simplertk2b board at all times, we will install str2str as a systemd service. Create a file sudo vi /lib/systemd/system/str2str.service with the following content:
[Unit]
Description=Stream RTCM correction messages from our base station to serial USB
After=multi-user.target
StartLimitIntervalSec=300
StartLimitBurst=5
[Service]
ExecStart=str2str -in ntrip://firstname.lastname-at-gmail.com@rtk2go.com:2101/CHE-Bern-Krauchthal#rtcm3 -out serial://usb-ardusimple:115200:8:n:1:
User=pi
RestartSec=10
Restart=always
[Install]
WantedBy=multi-user.target
Then install the service as follows:
sudo systemctl daemon-reload
sudo systemctl start str2str.service
sudo systemctl enable str2str.service
The two blue LEDs labelled XBEE>GPS and GPS>XBEE should now begin to flash, indicating that the Simplertk2b board is receiving correction messages. And after you position the rover with clear sight of the sky then the blue LED NO RTK should turn off after a while.
According to this article you can access one I2C bus only exclusively from one ROS node. Because we want to communicate with several sensors over I2C we need to create our own ROS node that then communicates with all the sensors we want to have (IMU, TOF, BMS, ...). We will make use of some existing packages which we will install using PIP.
pip3 install smbus
Install ROS according to the official guide. Make sure you have sourced your ros installation with source /opt/ros/noetic/setup.bash and then Catkin make your cloned workspace
cd /home/vboxuser/git/rtklawnmower/catkin_ws/
catkin_make
Then also source your workspace source ~/git/rtklawnmower/catkin_ws/devel/setup.bash.