The team spent considerable time developing the device's final design. The final design is not very different from the previous design, but it has been modified to make it more than just a hand truck. The new design has hooks added onto the frames, which hook onto the bucket handles and lift them from the ground instead of carrying the buckets into our device. The figure below shows the new design of the device. As for one of the team members, one of their tasks was to contact manufacturers in Peru to show them the sketches of the device to obtain prices for the fabrication of it. Out of the four services contacted, all said they could weld and fabricate the device, and a price of 180 soles to pay for labor was established. Following the presentation, the team received feedback showing the numbers to prove force reduction was necessary. This was ready for both the wheel and lever features of the device; however, it was not for the movement forces. The team began to make a quick body diagram of the alternative dolly to calculate the pulling force needed and compare it to the proposed design.
Figure 1: Final Device Design
The bicycle tires were first thought to improve the mechanical advantage of traversing obstacles due to their larger diameter. However, their lower weight decreases the force needed to move the device. Furthermore, an aspect the team had not considered is that the friction coefficients for bicycle tires are lower, which also makes the total force needed to move our device lower than that of an alternative hand truck. The team has also developed a new simple lever mechanical advantage to eliminate the need to manually lift the heavy buckets onto the device. This will reduce the total amount of force used to transport the water containers while using the device and reduce the stress on the San Juan de Lurigancho District users.
To move a standard hand truck up a 23-degree slope with two loaded water buckets would require around 331 N of force. However, the team's design would require 211 N of force, which beats the target of at least 25 percent force reduction. This is due to less tire friction, less overall weight, and a more extended lever arm that eliminates the need for unnecessary torques to maintain the device upright. In addition to the lever arm, the increased diameter of standard hand truck wheels reduced the required force to pull our device over a step by 26%, from 560 N to 400 N.
Heading into Capstone II, the team plans to acquire most of the materials and tools needed to construct the device. The team also plans to travel to the site and see exactly where the testing route will be. Lastly, all of the external resources and workshops will be contacted ahead of time to let them know that the construction date is upcoming. This will allow the team to stay ahead for most of Spring 2024 as long as the milestone tasks are completed proficiently. Additionally, the testing subjects will be contacted to schedule an appointment for the trial date. The plan is to have as many volunteers come out in one day as possible, eliminating the need to travel to the testing site multiple times. According to the team's feedback, the design does not need any adjustments, and the budgets seem fair. Currently, the budget will continuously be changed since one of the members is double-checking the prices in Peru. However, the prices are only getting cheaper, which will tremendously favor the team. Overall, the design is ready to be constructed and tested in the Spring 2024 semester, as shown by the drawing sheets below.
Figure 2: Front View of Device with Dimensions.
Figure 3: Side View of Device Frame with Dimensions.
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