Control / Sensing Hardware & Cost of Components

A project log for Low-Cost, Waterjet-Powered Robotic Speedboats

This project focuses on the development of open-source, low-cost, waterjet-powered robotic speedboats for education and research

New DexterityNew Dexterity 10/22/2021 at 17:450 Comments

To enable autonomous control of the platform we equip the platform with various sensors. In particular, the platform uses a 2D LiDAR (SICK TM510 LiDAR) and a monocular camera (Raspberry Pi Camera). These two sensors allow for detection of objects and landmarks in the environment. The two are used in conjunction with one another to increase the robustness of the computer vision system as neither LiDAR or RGB imaging offer great performance in dynamic environments with reflections like water. There are also two on-board IMUs, a GPS, and a magnetometer (provided by a Pixhawk 4 and Pixhawk 4 GPS Module) that provide the estimated pose of the platform. These sensors can also be used for active stabilization to further increase stability and reduce the chance of capsizing. 

A dedicated on-board computer (Nvidia Jetson Nano) can be used to collect and process all of the sensor data and generate movement commands for the on-board flight controller (Pixhawk 4), which interacts with all of the actuators on-board the speedboat. A block diagram presenting the interactions between the propulsion, control and sensing components can be found in Fig. \ref{hardware}.

The main propulsion power of the boat comes from two waterjets powered directly by brushless DC motors. These motors are controlled by electronic speed controllers (ESC) that receive a PWM signal from the on-board flight controller. Both systems are water-cooled from an outlet on the jet housing. Four servo motors control steering of each waterjet and the forward/reverse motion via reversing buckets. Actuators are powered by lithium-polymer batteries.

The costs of all components are presented in the table above. The Jetson Xavier NX and Sick LiDAR were not included due to cheaper alternatives that serve the same purpose with similar ability. The motors and ESC do not need to be as powerful with less than 50\% of their power being used.