Microcontroller Firmware

This folder contains all firmware that is written to microcontollers for the project.

hardware_interface 

This is the firmware that is written to a Teensy 3.2. The Teensy is connected to a computer via USB, and code running on the computer allows it to pull control effort messages from the ROS network. The Teensy is also connected to FrSky XJT radio transmitter, which allows it to send these controls to the car.

To launch the node, simply give the Teensy power and use the hardware_interface launch file:

Note that in order for this node to work, it need to be run on a Linux computer with that the docker container needs to be run with the --privileged option.

To use a different serial port (check ls /dev to see what it is named), modify the config file.

You can enable the cars with:

Then manually feed it controls with:

Building and Uploading 

Unfortunately, there are several steps required to build and upload code.

First you need to configure your IDE. This is best done outside of the Docker container. First, install the Arduino IDE, then Teensyduino. Make sure to install the PulsePosition library when installing Teensyduino.

Next, build the ROS libraries. Inside the Docker container, run:

Copy the generated ros_lib folder to <Arduino Location>/libraries/

Lastly, launch the Arduino IDE, load the hardware_interface.ino project inside the scripts folder, set the target board to the Teensy 3.2, and click upload.

Binding the Radios 

Binding the radios to the cars is a somewhat tedious process. There is a very precise set of instructions to follow, and you may need to do it several times in a row, until everything goes exactly right.

Power everything off (radio + car)
Ensure the dip switches on the radio are set to 1-on, 2-off
Hold down the white button on the radio and power it. It will beep and blink
Hold down the button on the car’s receiver, and power it. It will also blink
You can release both buttons
Power off the car
Power off the radio
Power on the radio
Power on the car If it worked, the car’s receiver will have a solid red light. If it didn’t work, you’ll need to try again.

Setting the Radio Failsafe 

If the radio signal is lost, the car will automatically go in to a failsafe mode. This mode needs to be programmed so that the default action is to do nothing (as opposed to go absolutely bonkers and run into walls, which has a good chance of happening if the failsafe is not explicitly set). The procedure is simple. Run the hardware interface and manually publish an effort message with the field’s zeroed (do this on a frequency like 10 Hz). Power on the car and within a second or two after power it, click the button on the receiver. All done.

Programming the ESCs 

The ESCs (Electronic Speed Controllers) in the cars are very advanced. They’re over-powered for what we’re doing, and are some of the best on the market. They are highly configurable through a simple user interface.

Download and install Castle Link on a Windows computer. Use the USB adapter that we purchased with the ESCs to connect it to your computer. The battery does not need to be connected to the car, and you will unplug the ESC from the receiver to connect it to your computer. In Castle Link, connect to the car. Then go to File->Load Settings, and load esc_settings.dat in the config folder. Click Update in the bottom right to send them to the car.

After programming them, the endpoints need to be set. This tells it what control input maps to what speed. The procedure is a little complex, but not too bad.

Power off the car and hardware interface
Set the throttle throw to 500 on the hardware interface config
Launch and enable the hardware interface
Manually publish an effort message with 1.0 throttle effort (at 10 Hz)
Power on the car With the wheels off the ground, it should make a lot of beeping noises
Manually publish an effort message with -1.0 throttle effort (at 10 Hz)
Manually publish an effort message with 0.0 throttle effort (at 10 Hz)
Power off the car and hardware interface
Revert the throttle throw to what it was previously at

After step 7, the car should have made some noises, then stopped beeping. If you run the car normally and it makes a lot of noises and doesn’t move, or if it goes way too fast, then you likely need to do this procedure again.