02.5 - Implementation

From the result of the initial and final kinematic analysis, we learned the second assembly prototype from design process section has better in-and-out-of-water trajectory for the oar and great force exerted to the water. Below are details of the implementation process of the final design.

Fabrication

We 3d printed our linkages, boat, gears, and connection pieces since we had access to 3D printers and appreciated the ability for greater customization and iteration. This allowed us to test different component combinations for the best outcome.

For prototype purpose, we used PLA filament for 3D printing due to ease of access. For the final prototype, we printed the whole assembly (except for Arduino holder) with PETG HF due to waterproof requirement. Since our assembly requires tight fit for bearings (inner diameter of 6mm and 8mm), when we switch 3D printing filament, we did a bearing test print to ensure the hole size is best fit for the bearing.

Figure 1. final design test print with PLA filament

Figure 2. final assemble print parts with PETG HF

Assembly

We first assembled our final four bar linkage, then attached each one to an oar. The connection is a ball-joint since we want the oar to move freely in a 3D path. These are all held together by our base frame which acts as our boat body. We add plastic bottles to aid in floatation.

Figure 3. CAD image of ball joints

Figure 4. Physical image of the base and ball joints

We also use a custom set of bevel gears with a 4:3 gear ratio to step motor speed down. Our custom bevel gears sit on a central undriven shaft for alignment purposes. They have roller bearings on the gear-shaft interface so that they are in a set position but can rotate freely relative to the other side.

Figure 4. CAD Image of bevel gears with 4:3 gear ratio (input : output)

Demo Video 1: Gear testing with 4:3 gear ratio

Electronics

We used a pair of 12V 0.6A 50 RPM DC gearmotors to move the oars, one for each side. These motors were driven by a L298N DC motor control board. This control board responded to instructions published by an Arduino Uno based on the position of a joystick. The entire boat was powered by 1x 12V Lithium-Ion battery pack.

Figure 5. Wring diagram of the motors, motor driver, Li-Po battery, joystick and Arduino.

Final Arduino code: https://github.com/mac785/RMD-Longboat-Arduino/tree/main

Unique Features

We embedded 8mm inner diameter linear bearings inside the ball joints so that the oar can dynamically move in and out of the wall position relative to the base. In addition to that, we utilize rectangular bottles to help our boat float. Since the bottles have a flat surface with a rigid wall. It will be ideal for enlarging the boat size without increasing mass, which makes the boat float.

Figure 6. Physical prototype of ball joints (ID 8mm linear bearings are embedded inside) and rectangular bottles.