Post #7: Final Project Blog

During the work period of March 26 - April 16, our team has finally received the large sprocket we have been waiting for from McMaster (though it is only 45 teeth as opposed to the intended 48 teeth) and finished construction on our roundabout prototype. We have also collected validation testing data for the prototype as well. Figure 1 shows a top view of our finished prototype, figure 2 shows the underside of the rotating platform, and figure 3 shows the generator setup.

Figure 1: Top view of the roundabout.

Figure 2: The underside of the rotating platform.

From figure 2, you can see that a washer and bolt has been used to pin the large sprocket down to the underside of the rotating platform. Since the wood blocks will not be spinning, it will not be an issue for the chain to go in-between them.

Figure 3: The generator setup using L-brackets and springs.

L-brackets with grooves to adjust screw positions were used to place the generator. The reason for the springs is because the large sprocket is not perfectly centered on the roundabout, which makes the generator shift periodically as its spinning so springs were used to let it move more freely and then pull back to its original position as the chain tighten and slacks. For our power validation testing, we used a phone's gyroscope to measure the RPMs on the rotating platform and then matched peak RPM values to the peak voltage and current values from the multimeter. Figure 4 below shows our results.

Figure 4: Peak voltage and current values during data collection.

The reason why the RPMs are different for our peaks in figure 4 is because we were not able to measure current and voltage at the same time, and spinning the roundabout at an exact RPM consistently was not achievable. From the voltage and current values above, we know that we can at least get 6.22 watts (multiplying voltage and current) from our roundabout at peak levels. This surpasses our 5W power target. For our deflection validation testing, we used adjustable weights on the edge of the rotating platform and measured the gap between the two platforms using a caliper to see any changes in distance. Figure 5 below shows our results.

Figure 5: The deflection results from adding weight to the rotating platform.

Increments of 10lbs were used but the adjustable weights only go up to about 100lbs max, so we had a team member stand on the platform with and without a weight to get the higher end values. These results are satisfactory because we intended for the roundabout to be able to support up to at least 200lbs of human weight with 1cm of deflection at most. From figure 5, it can be seen that the maximum deflection was 0.517cm.

At this point in our project, our team has managed to achieve its goal of constructing a roundabout prototype that can generate power from being spun, and has successfully passed validation tests for its 5W peak goal and 1cm maximum deflection, so we have met our goals. One of the major shortcomings of this prototype would be its resistance to free spinning for long periods after being spun, but this is an improvement that we do not believe can be addressed in the remaining time we have. A more specialized ring bearing would have helped free spinning after starting, but that would have most likely increased our expenses considerably. A video of the prototype in action has been included below.