My daughters and I have built a number of boat projects with an assortment of Arduino, ESP-8266, Bluetooth and RFI components. I believe that this version using a Raspberry Pi and NodeRed offers one of the simplest solutions. This sailboat used a basic catamaran design with a Raspberry Pi mounting inside a waterproof container. Using NodeRed dashboards you can control the sailboat’s rudder from a smart phone. The complete NodeRed logic consisted of only 6 nodes.
Building the Sailboat
There are a lot of different building materials that you could choose from. K’Nex construction pieces are lighter than either Lego or Meccano and they allow you to create reasonably large structures with a minimal number of pieces. If you do not have access to K’Nex pieces then popsicle sticks and some card board would offer a good low cost solution.
To build the sailboat we used:
• K’Nex building pieces
• 4 plastic bottles
• 1 small plastic container with a lid
• Duct tape
• Garbage bag
• Low torque servo
• Raspberry Pi Zero W or Pi 3
• Small USB phone charger
The base of the sailboat was a rectangular structure with 16 down facing K’Nex pieces that allowed plastic bottles to be duct taped in place.
A few K’Nex pieces were used to create a compartment for the servo, and wire was used to secure the servo in place. A rudder was built by screwing a small piece of wood into the servo arm.
A garbage bag was cut to the required size and taped to the mast. The boom had a swivel connection to the mast and guide ropes were connected to both the boom and mast.
Servo and Rudder Setup
Only very low torque servos can connected directly to Rasberry Pi GPIO pins.
An example of a low torque servo would be the TowerPro SG90 ($4) that has a torque of 25.00 oz-in (1.80 kg-cm). If you have larger torque servos you will need to either use a custom Raspberry Pi servo hat (there are some good ones on the market), or you will need to use a separate power and ground circuit for the servo.
The wiringPi tool gpio can be used to control the servo. This package is pre-install in the Raspbian image, or it can be manually installed by:
sudo apt-get install -y wiringpi
Servos typically want a pulse frequency of 50 Hz, and the Raspberry Pi PWM (Pulse Width Modulation) pins have a frequency of 19200 Hz, so some range definitions and scaling is required:
gpio -g mode 18 pwm #define pin 18 as the PWM pin gpio pwm-ms #use 'mark space' mode gpio pwmc 192 # set freq as 19200 gpio pwmr 2000 # use a range of 2000
The gpio pwm commands are not persistent after a reboot. A simple solution for this is to put these commands in the Pi user login file of: $HOME/.bash_login.
After the pwm setup commands are run you need to do some manual testing to define your different rudder (servo) positions (Figure 6), such as “Hard Left”, “Hard Right”, “Easy Left”, “Easy Right” and “Straight”. The pwr timing numbers will vary based on your requirements and servo arm positioning, for our sailboat we used:
gpio -g pwm 18 200 #straight gpio -g pwm 18 260 #hard left gpio -g pwm 18 140 #hard right gpio -g pwm 18 230 #easy left gpio -g pwm 18 170 #easy right
NodeRed Logic and Dashboards
NodeRed is pre-installed on the Raspbian image, but it will need to be set to autostart on a Pi reboot: sudo systemctl enable nodered.service
On the options button (far right), by selecting: View -> Dashboard , you can define and change the web dashboard layouts.
To create logic, nodes are selected from the left node panel and dragged and dropped on to the center flow panel. Logic flow are then created by clicking and joining together different inputs and outputs on the nodes. If a dashboard node is dropped on the flow panel it will be added to the default web dashboard. The gpio -g pwm commands can be called using the exec node. The button dashboard node will pass the defined payload value, for example a “Hard Left” 260 is passed when the button is pushed. The button’s payload value will be appended to the exec command to make a complete gpio -g pwm servo position command.
Once you’ve completed your logic setup press the Deploy button on the top right to make your configuration live and ready to test.
The final step is to enable a smart phone or tablet to connect to the Raspberry Pi, this can be done by either making the Raspberry Pi a WiFi access point or by tethering the Pi to a cell phone. There are some great guides on how to setup a Raspberry Pi as an access point. For this project the simple tethering method was used. Once the Pi is tethered to a phone, the PI’s IP address can be obtained from the hotspot users list.
The NodeRed dashboard is accessed on your phone by: http://pi_ip_address:1880/ui .
Assuming that everything is connected correctly you should be able to control the sailboard with your phone.
Once you’ve mastered the basic NodeRed and sailboat construction other projects such as motor boats, iceboats, airboats are possible.