Preliminary Design Review Report
Executive Summary
The purpose of the labs thus far have been to analyze the different components of the AEV, as well as different designs, to narrow down ideas for the AEV that can best complete the mission objective. This process was composed of several different specific objectives that helped to direct the lab work: what propeller type had the best performance, how accurate were the reflectance sensors, how is the design impacted by the team’s criteria, how is the code impacted by the design and physics of the AEV. The propeller has a significant impact on the thrust and power efficiency of the AEV which is why it is crucial to choose the best one. Also, the accuracy of the reflectance sensors is crucial so that the AEV moves to the correct position indicated by the code consistently. The team’s criteria are important since it is used to help make decisions between competing AEV designs. It is also important to consider how aspects like mass, balance, and inertia impact the physics of the AEV since the code needs to incorporate adjustments for all of them. These objectives help to maximize the AEV’s performance in picking up and delivering the R2-D2 unit across the track.
The AEV is important to the Alliance since they need a vehicle that can transport R2-D2 units with limited resources. Power is limited on the planet which is why it is crucial to have the AEV be as efficient with its power supply as possible. Another important factor is its ability to run along either track consistently. To meet these objectives, the AEV designs will use as little energy as possible without compromising the primary objective. Also, the code will account for all inhibiting factors while also making sure that the AEV stops at the appropriate locations and for the proper amounts of time.
The current situation has two competing AEV designs which are similar in every way except for the addition of a 3D printed dome and angled pieces in the front. Between both designs the 3030-model propeller was selected due to its superior thrust and power efficiency. The design with the additional parts has a greater mass than the other design, leading it to have a poorer energy to mass ratio. In addition, this design tends to coast more after the application of the brake. An observation that applies both designs is that they are relatively slow but not to the point that they become over the time limit. The current code has the AEV stop before the second sensor, wait for the gate, coast into the cargo magnet, wait for five seconds, return to the gate before the sensor, and return to the drop off area. However, some alteration is still needed to make the process repeatable as the AEV does not consistently stop before the second sensor on either the outbound or return trip.
The lab scenario could be improved by incorporating a time element into the objectives. Currently it is satisfactory if the AEV completes the task in under two and a half minutes. It would make sense that the Alliance would want the droids to be delivered as soon as possible, though not compromising efficiency or effectiveness. The time does not have to be reduced necessarily, but it could be added that the droids should be delivered as soon as possible. Another idea could be to give bonus points based on how fast the AEV completes the task under a certain time, encouraging teams to add this other element to their AEV code and overall design process.
Introduction
The purpose of the labs in the AEV project have been to test the different components of the AEV, analyze different designs, to decide upon the AEV that can best complete the mission objective through scoring practices. This process was composed of several major tasks that helped to direct the lab work: what propeller type had the best performance, how reliable were the reflectance sensors, how does the design decided by the team’s criteria, how is the code impacted by the design and physics of the AEV.
Results
The two Advanced Energy Vehicle designs that were analyzed by the group were relatively similar to each other in terms of appearance and basic construction. Both designs utilized the cross or “X-shape” piece as the main structural foundation with the “T-shape” arm used for both as the wheel mount for the overhead track. The first AEV design, pictured below as Figure 1, was a basic skeleton derivative of the further refined second AEV design.
The first design features an open layout with the Arduino unit attached on top, the battery pack hung underneath, and the two motors mounted to 1’’ x 3’’ rectangular pieces in the rear (pusher configuration). The second AEV design, pictured on the next page as Figure 2, included increased stability due to the addition of several components.
In addition to increased stability due to a more slender, aerodynamic design, the additional components, notably the dome shaped piece and the two forward trapezoidal pieces, were added to enhance the creativity of the AEV appealing to the Star Wars theme of the MCR with a Millennium Falcon inspired design. The second design also included a double bracket piece attached to one trapezoid in the front of the AEV to attach to the magnetic trailer system. The additional weight brought on by the added components for the second AEV design resulted in alterations to the code which will be discussed later.
The team’s initial four designs created in Lab 4 were screened for performance, efficiency, appearance, cost, etc. and were initially concentrated down into the current AEV #1 design and a combination of two previous designs. The combination design eventually evolved to become very similar to the first AEV design and would later become the AEV #2 design with the addition of the Millennium Falcon components.
The team’s concept scoring sheet from Lab 5 is pictured on the next page as Table 1 and depicts the initial four designs considered by the group.
Table 1: Lab 5 Concept Screening Sheet
The reference design was a standardized AEV design that the group used to juxtapose their own designs. “Tom’s Design,” because of its comparatively good screening score went on to become the reference design in the concept scoring matrix, pictured below as Table 2. Eric’s and Charlie’s designs were combined to create the combination design which led to the development of the AEV #2 design.
Table 2: Lab 5 Concept Scoring Matrix
When observing the different designs perform on the track the lab group first tested out design one. When design 1 runs the design starts off slowly and gathers speed over time. Throughout the turn the design remains stable without any wobbling that could result in a potential fall thus causing harm to the vehicle. The repeatability of this design stays consisting throughout testing and hardly varies trial to trial. Below can be seen a graph of power supplied over time. The graphs of the two are similar due to the fact the code used for the graph only involved a constant output of power over a period of time not distance so only one graph is shown.
Figure 3: Supplied power vs time
When observing design two run the track using the same code the two vehicle behave incredibly similar. The main differences between the two designs is weight, and when testing the difference can be seen clearly. The second design speeds up much slower compared to the first and stops slower. The lab group expected this change because of the excess weight placed upon the AEV. While the weight changes the actions of the AEV the energy consumed by the AEV stays relatively the same. After talking the lab group came to the conclusion that this was because of the way the code is written; it is written in such a way that the motors are on for a set amount of time in the beginning in order to first get the AEV going. This initial jolt of energy allows the AEV to overcome static friction and get the AEV moving so when the motors remain at a constant speed the AEV is able to still accelerate quickly.
Figure 4: Propulsion vs Advanced Ratio 3030 propeller
When the lab group saw the results from the wind turbine lab the lab group came to the conclusion that the 3030 propellor works best at a speed that is not too fast. So in order to take this factor into account the lab group decided to slowly sleep up the AEV in order to keep efficiency up. This allows the propellers to use less energy while at the same time keeping efficiency high.
The Performance test allowed the lab group to come to a fairly important decision about the coding. The Performance test caused the lab group to look at the preferred method of stopping.
During the performance test the lab group noticed some variability in the distance the AEV took to stop. It appeared the longer it took the AEV to come to a rest the more inconsistent to vehicle was. This led to the conclusion of stopping the AEV with a backwards thrust from the motors. This change in code allowed the location of where the AEV stops to be more accurately determined which is important for the opening and closing of the gate. Even a couple inches off could either cause the AEV to stop short or go to far.
Conclusion & Recommendations
Upon completion of the lab, it is reasonable to infer that the chosen AEV should be modeled after design 2. When looking at the scoring matrix design 2 received a rating of 4.2 compared to design 1 with a rating of 3.2. Once the design was chosen it was important to take a look at the code to see what can be tweaked and what still needs to be altered in order to make the code run as functionally as possible. The added weight proved to be crucial because the AEV was more stable going around the corners and the code became more consistent. Moreover, the graph of figure 5 shows the relationship between supplied power and time. The graph can depict how by using a reverse thrust function and allow the AEV to stop over time, this creates a very linear braking power and the AEV stops consistently at the same location. The final brake command proved this where the AEV dropped 2.5 watts over a .1 second period. Also the
There are problems with this data, however, as a result to the battery. After continued use of running the AEV the batter will begin to drain and start to skew the data and accuracy of the test code. When this happens the AEV will no longer stop at the correct locations because it does not have the power to do so with the reverse thrust commands. The AEV needs to start at the same location every time for the code to be correct. Should the AEV be off by an inch when stopping, the second sensor could trigger at the gate and the code would no longer be fully functional.
The problems that were discussed have very simple solutions. Should the AEV begin to have different results, the group can replace the battery with a new one and this way the supplied power to the AEV will be consistent with the given code commands. In terms of the starting position, the group decided to line up the back wheel on the tape at the starting location and by doing so, this gave the best results over the different trials when the group ran the code.
With the given results, the AEV is shown to be very consistent with stopping. In order to improve on this, in the future the group is looking into installing a servo in order to stop the AEV on top of the brake command with the reversed thrust. The added brake would make the AEV even more consistent because the AEV will have more stopping power and would leave less chance for the AEV code to not work improving the consistency of the code.
Although the group was able to complete the performance test, the group was not able to fully complete it at that time. The arduino kept malfunctioning and the group had to replace the board. This meant that although data was recorded and the test was completed, with the new arduino board the results could have been slightly different. The group found out that with the addition of the new board the data remained consistent , however, it was worth noting that at the time the test might not have been fully complete because of this.
The group recommends checking all equipment prior to testing so that the issue can be resolved quickly and efficiently. The faulty equipment was not an issue in terms of results in this case, however, this could have been a very detrimental issue that would have altered the data from the performance test, the scoring matrix, and the choice of what design to choose.
Appendix
Table 3: Team Schedule
Figure 5: AEV #1 Orthographic Views
Table 4: AEV #1 Bill of Materials, Cost, and Weight
Figure 6: AEV #2 Orthographic Views
Table 5: AEV #2 Bill of Materials, Cost, and Weight
