Construction Phase:

Electrical:

The initial electrical design of the boat focused on successfully achieving full function of the infrared sensors, electric motor, ultrasonic sensor, and Arduino. Focus on weight reduction and circuit efficiency would occur in the modification phase, as this initial circuit would be dissected and its redundant or unnecessary parts removed with each design iteration making the end goal clearer. Many of the electrical methods selected were chosen because of reduced cost and simplicity of the implementation.

In initial construction, the motor was controlled via an Arduino motor control board. This board managed all power issues (current and voltage transients) and enabled forward and reverse control of the DC motor. The motor board received power exclusively from six 1.2V AA nickel metal hydride (NiMH) batteries. The NiMH were heavy, weighing about four times greater than lithium polymer batteries in the same price range, but they reduce cost and have greater capacity at 2300mAH vs 840mAH respectively. The Arduino received power from a 9V alkaline battery. Through the five volt rail on the Arduino, the sensors were supplied power. Figure ## shows this circuit fully constructed.

All circuits were constructed on a mini breadboard. The breadboard enabled quick prototyping of the circuit and offered easy modification compared to soldering the circuit. The weight advantage of using perforated board (12 grams) versus breadboard (17 grams) was deemed insignificant to the ability of being able to quick swap components and change circuit layout.

Modification Phase:

Electrical:

The boats electrical design went through a rigorous test of practicality, functionality, and ability to meet requirements. The motor board enabled easy control of DC and servo motors, while handling many current and voltage noise issues. However this circuit board had many limitations. The torque water applied to the propeller significantly increased the current draw to levels above the specification of board components. By placing an amp meter in series with the motor, current draw during operation underwater

were found to exceed 1.2A, while the boards H bridge specifications maxed out at 650mA. The boards’ reliance on a secondary power supply significantly increased weight and the circuit required large floor space to accommodate all components. This led to the first phase of modifications:

To reduce weight, and to reach current requirements, a MOSFET was substituted for the motor control board. The MOSFET was selected because it enabled control of current to the motor, via the MOSFET gate, which can be saturated by PWM signaling from the Arduino. The motor is only required to provide thrust in one direction, and thus no H-bridge would be required for switching current direction. The current and voltage specifications for the MOSFET were selected to be greatly outside the maximum values seen in practical use to ensure no issues (30A and 60V). Figure ## shows the modified circuit.

The circuit created after phase one modification improved weight, and eliminated current issues for the DC motor but other issues became apparent. The servo motor received power from the Arduino 5V rail. This voltage line can supply up to one amp of current but when operating the rudder, torque applied to the servo could push the total current draw on the motor above this threshold, causing the Arduino to reset. The current transients from the servo motor also have a negative effect on sensor output. The fluctuating current and voltage creates high frequency noise on the power line for the sensors. The fluctuations effect the voltage threshold on the sensors conversion circuit, causing noise and incorrect values to appear on the output. The ultrasonic sensors in particular were extremely susceptible to power changes effecting the quality of output data. To remedy this issue, a second phase of modifications took place. The goals of this phase were to further reduce weight and fix current draw issues via component isolation.

The NiMH batteries were replaced with a 480mAH lithium polymer (LiPo) battery, reducing weight by 120 grams. This decreased the overall capacity available to the boat, but increased performance due to less weight.

To address the servo variable current, the servo was removed from the Arduino 5V rail and placed on its own power rail that utilized a linear voltage regulator to drop the 7.4V from the LiPo to 5V and supplied the servo up to 1.5A exclusively. This improved sensor output during servo and motor operation as the Arduino isolated them from noise on the power rails and properly maintained current and voltage to all sensors.

The circuit in figure ## depicts the final circuit. The infrared sensors used to track the boats stern and bow were replaced with two ultrasonic sensors. This was done to improve range and because infrared sensors displayed greater variability due to moisture absorbed during operation. The front of the boat utilized an infrared sensor however because its output contained less overall noise (outliers in distance readings) which was important in properly detecting a wall before performing a left turn.

Prediction vs Real

The initial circuit design was largely based on theoretical knowledge and previous experience, but neither fully prepared us for electrical issues that would arise. The sensors were extremely sensitive to voltage noise on their power lines. When coupled with the servo motor, which varied its current draw, the sensors would read incorrect values. This behavior was not anticipated and caused many delays.

The sensors were expected to operate fairly consistently, but moisture from operating around water significantly affected the PCB traces and reduced the quality of output from the sensor, which went on to affect the ability of the boat to guide itself.

When in operation, the boat could act unexpectedly if sensors output noise to the code. Most noise could be filtered, but water splashes that landed within openings of the sensors (which could not be effectively water proofed) would lead to adverse behavior in rare cases. This occurred in competition where water splashes incurred during a collision subjected the boat sensors to water damage. This reduced ability of the boat to operate effectively and directly affected performance.

Lessons learned

Electrical:

The lessons learned in electrical design helped solidify fundamentals and establish key experience. In the initial design, many assumptions about the function of components were made, such as one amp being sufficient enough to power a servo and three sensors. Most alternatives solutions were also overlooked for pre-designed solutions such as the motor control board. These led to many issues detailed in the modifications sections and the lesson that thoroughly researching alternatives and looking with great detail through data sheets is a necessity to mitigate important issues related to electrical specifications. Simply performing calculations based on theoretical set-ups will not help to model real life situations.

Another key lesson is leaving your design to be modifiable and scalable. A design which can accommodate new components and be easily configurable enables issues to be debugged and improvements to be implemented faster. The initial circuit designed did not incorporate this, and when issues arose, a complete tear down was required to find the issue and fix it.