Blog Post #4

Finishing the first semester, our full design for removing surface pollutants in small bodies of water has been completed, as seen above. The most important components by function are the belt and the trash container. The belt supplies the means for separating debris from water and the container allows the user to remove the debris. When the device is being used, the belt will rotate against the water flow while attached flights underneath, scoop and guide the debris up the belt and into the container. Emptying the container is the major step done by the user that completes this solution.

For the water wheels, the most important calculation was for the head. The head for overshot water wheels would be the height difference in the water which is where the water wheel gets its energy. For undershot water wheels, like this one, this is related to the average speed of the water below it, which was estimated to be 3 ft/s. From here, the optimum diameter was found to be between 4.8 to 9.6 inches where the larger the diameter the better. We have decided to round that up to an even 10 inches to make the design easier to construct. We know that having more surface area on the blades allows for greater force to be experienced and used by the water wheels, so we chose to increase the length of the water wheels to just below the total maximum width of the device.

Using a stream velocity of 3 ft/s, a water wheel width of 11 inches, a water wheel diameter of 10 inches, a blade thickness of 0.5 inches, and a shaft diameter of 2 inches gave us an optimal angular velocity of 55.6 rpm for the water wheels shaft. We selected a gear ratio of 9:5, with the smaller gear on the belt shaft to make it rotate faster. Using the gear ratio, the angular velocity of the belt shaft is 100.08 rpm. The diameter of the sprockets was chosen to be 5.9 inches, so the belt speed was found to be 12.89 ft/min or 2.58 in/s. This theoretical belt speed is sufficient to pick up trash at an appropriate rate.

With the stream velocity calculated, we were able to obtain the force load on each of the blades from the water to be 8 N applied horizontally. The finite element analysis (FEA) of the water wheel is shown below to the left. Applying polylactic acid as the material, the stresses shown indicate that there isn’t too much stress or tension on the blades. Also worth noting is that the wheel will be hinged allowing free rotation thus allowing minimal stress and more movement. This FEA confirmed that the water wheels will move as calculated without any interference due to material properties of using 3D printing.

Another FEA was completed for the gears as shown above to the right using the same material as the water wheels. At first, we were debating whether to use aluminum gears or 3D printed gears to save costs while also maintaining durability and stability with the initial torque applied from the water wheels. With the calculated angular velocity from the water wheel shaft, the torque the bigger gear applies on the smaller gear is roughly 5.97 Nm. As seen in the FEA, the gears with PLA properties are under a bit of stress. This is under the assumption that the smaller gear is fixed, however, the smaller gear will be rotating. Allowing it to be fixed for analysis purposes, shows the maximum stresses involved, confirming that the gears under PLA properties will not break or fail with the torque applied.

To prepare for the Spring 2021 semester, we are planning to take care of a few time consuming tasks over the winter break. This will decrease the amount of dead time where we have to wait. We will purchase the belt and its accessories over the break so that it will arrive at the start of classes in January. As we are not buying a belt directly from a manufacturer due to the high cost, we will need to ensure the different belt parts—belt, sprockets, flights—we buy are compatible and can be assembled. The flights on the belt may cause undesirable drag, so we may need to puncture them to allow the water to flow.

We also will begin correspondence with the 3D printing office over the break so that we can get approval and begin printing as soon as possible. We are doing this so that we are not waiting in a long line behind other students. Other main issues we may face all relate to the response of the pandemic. As our design is an attachment for a pedal boat, most pedal boat rentals areas are closed due to lockdown. In terms of building the physical attachment, we have the necessary tools and resources that are available to us. However, when it comes to testing and validating our device, we will have to wait for the lockdown to end, at most, by March. Most of these challenges are uncertain but are still a possibility and through the duration of winter break, our team will be looking into worst case scenarios and how to overcome them in the case it occurs to maximize our productivity during the execution of our design.