Controls & Microcontroller Design
The Controls & Microcontrollers team is responsible for all the software involved in moving the boat’s motors based on a desired movement. This is split into two pieces: control algorithms and microcontroller design. In addition, the team works on the sensors that feed data into the algorithms used.
Sensors
The team currently uses a VN-300 INS sensor to obtain positional and heading data. Given the narrow paths the boat must pass through, obtaining reliable, accurate positional data is key. Out of the box GPS systems are typically not accurate enough for this use case, so the team is experimenting with methods such as RTK positioning and Kalman filtering.
Controls
The group designs, implements, and tunes our own control algorithms to determine what signals need to be sent to the motors to follow the path outlined by AI. We use a combination of pure pursuit and PID. Pure pursuit is a path tracking algorithm which maintains a “lookahead” point on the path some set distance away from the boat. As the boat moves, the point advances along the path, so the boat is always chasing it. This results in a more natural, smooth path of movement.
Pure pursuit typically outputs the linear and angular velocity the vehicle should move at in order to head towards the lookahead point. However, we found that controlling on velocity produces rough and shaky movements due to the sensitivity of our IMU, a sensor which produces velocity readings. This year we decided to transition to using heading as the variable we monitor. The algorithm calculates the error in heading as the difference between the boat’s current heading and its heading if it were pointed directly at the lookahead point. We then apply PID control to reduce this error. PID (proportional, integrative, derivative) control is a tunable equation which takes an error as input, multiplies the error, integral of error, and derivative of error by some constants, and outputs the offset which is then converted into PWM signals sent to move the thrusters.
When new features eventually get introduced onto the boat, such as a robotic arm, the controls group will experiment with more complex control mechanisms.
Microcontrollers
This group also writes our microcontroller firmware. This code facilitates communication between the remote controller, the main onboard computer, and the motors by translating commands to PWM signals that are sent directly to the motors. With each new capability added to the boat, such as the skeeball shooter and water gun, new features are coded onto the microcontrollers. Currently, we use an Arduino uno microcontroller for receiving signals from the remote controller and writing signals to motors. We also use a MicroMod ESP32 processor for our GNSS data.