Critical Design Report

Submitted to:

Professor Wyslouzil

GTA Alec Sichko

Created by:

Team B

James Amann

Dan Buergel

Luke Johnson

Ryan Linnabary

Engineering 1182

The Ohio State University

Columbus, Ohio

April 20, 2015

Executive Summary

Jurassic park has reopened and is in need of an Advanced Energy Vehicle that can navigate through the park. The AEV must ferry visitors to Jurassic Park in a safe and timely manner. The AEV should also be capable of pulling a caboose full of dinosaur eggs, and should be able to run consistently with no mishaps. Ultimately the AEV must complete this scenario in the most efficient way possible as there is a limited supply of power on the island. So in order to find the most efficient AEV, small scale design prototypes should be tested. Once the most efficient and reliable design has been produced, the park may construct the vehicle full-scale. This design process is often used in many industrial settings. It should be cheaper to conduct testing on a small scale rather than a larger scale. Thus, this type of testing is important to engineers and researchers in the scientific community.

The group performed a series of tests in order to develop the final design. The group first brainstormed two different AEV designs. These two designs can be seen in Figures A6, and A7 in the appendix. Both designs used the test scenario and code for the first part of the test. The group recorded data from both runs, and compared data. The first design did not perform well on the track, it did not move at a good rate, and was not balanced well. The second design moved better on the track, and was better balanced. Both designs produced similar amounts of total power used. But the first design does not meet all of the design requirements. One of the propellers was mounted on the front of the AEV, and left no room for the metal brackets that couple to the caboose. So that also ruled in favor of the second design since the AEV met all of the requirements.

The second test involved the code for the AEV. The group wrote a set of code that would allow the AEV to complete the entire course. From previous testing the group knew reversing the motors used a large amount of energy. So the group wanted the AEV to coast as much as possible to conserve energy. At first the code appeared to work, but as the battery power lowered after each run, the AEV failed to complete the scenario. The AEV also functioned differently on other tracks. The AEV had difficulty stopping in a controlled location and was unable to complete the entire run. The group decided that the AEV needed a better way to bring the AEV to a stop, but still conserve energy.

The third test called for making the AEV more efficient and less expensive. But the group added a servo motor that would function as a mechanical brake. The servo proved to be a more reliable braking method, and also proved to be more efficient than reversing the motors. When compared to the coasting method used in the previous test, the servo brake did use more energy but made the vehicle more consistent. The AEV was capable of completing the run after installing the servo, and a small amount of coasting was still used before the servo engaged.

It would be recommended to have the CDR due on a different day, than the presentation and project portfolio. A lot of preparation work is required for all. Maybe modify the schedule so the CDR is due a week before project portfolio, and the presentations. This should give enough time adequately complete all assignments, without taking away study time from other classes.

Table of Contents………………………………………………………………………………………………2

Introduction……………………………………………………………………………………………………..3

Experimental Methodology……………………………………………………………………………….3

Results………………………………………………………………………………………………………………3

Discussion………………………………………………………………………………………………………….6

Conclusion and Recommendation……………………………………………………………………..7

Appendix……………………………………………………………………………………………………………9

Introduction

Group members worked together to make an efficient and reliable AEV. The AEV should be able to complete the all of the objectives. Group members produced and tested two designs. A choice was made for which AEV design to continue development. Students then worked on a new code that outlined the mission scenario. The goal was for the AEV to complete the run. After the AEV successfully completed the run, students worked on making the code, and AEV design more efficient. Once all of these steps were completed, the group completed the final test. The test was to see if the AEV was capable of completing the entire run.

Experimental Methodology

Group members designed two different AEVs. Both of these designs would use the same code for testing. The code would use most every command available. This would provide a fair test between the designs, and would also show which commands in the code were inefficient. The two AEV designs were tested on the track using the same code. After the run was completed students retrieved eprom from the AEV, and also generated an input power versus time graph. An example of this type of graph can be seen in Figure A8, located in the appendix. The eprom data could be imported into excel, and calculate incremental energy used for each command in the code. The input power versus time graph allowed group members to see which commands were inefficient. It would also show the length of time it took to complete the run. The eprom data could be used to calculate many different variables. Group members could calculate the incremental energy per unit of time. Then group members summed up the incremental energy to find the total energy used by the AEV. After reviewing the information, Group members chose the AEV design that used less energy.

A code was developed, it should allow the AEV to complete the mission objective. Students tested the code, and would make modifications after each run if the AEV did not finish. Students would continue to test until the AEV completed the course. After the AEV was capable of completing the course, students would try to cut out inefficient sections of the code, or modify the AEV to reduce cost, and improve efficiency. Students were required to complete a final run, the AEV would be graded based on its ability to complete the course. Data would then be recorded after the final run, and an energy per kilogram ratio calculated.

Results

The group developed two different AEV designs. The first AEV design is located in Figure A6 of the appendix, and the second AEV design is located in Figure A7, which is located in the appendix. Both designs weighed approximately the same amount, about 0.32lbs. The first design cost about $2 more than the second design. The first design did not travel fast on the track, it appeared to start slow. It was unbalanced, because it leaned to one side of the track. The second design moved better on the track, when compared to first. It appeared to accelerate quicker, this allowed it to complete the code quicker. After each run, the group generated input power, and propulsion efficiency versus time graphs. The graph for the first design is located on the next page seen in figure A1. The graph for the second design is located on the next page seen in figure A2. The graphs look similar, but it should be noted that the second AEV finished the code about five seconds faster than the first design.

Figure A1: Efficiency and Power versus time utilizing design 1

Figure A2: Efficiency and Power versus time utilizing design 2

Both designs utilized the 3inch propeller. The group decided to use the 3 inch propeller because it achieved a large advance ratio that maintained larger amounts of efficiency. The smaller propellers did not achieve above 10 percent efficiency, while the 3 inch propeller stayed well above 12 percent. The propulsion efficiency versus the advance ratio can be seen on the next page in Figure A3.

Figure A3: Propulsion Efficiency vs. Advance Ratio

The second test involved the code. Students wrote a code that allowed the AEV to traverse the track. The code utilized coasting as the main method of stopping the AEV. The group wanted to avoid reversing the motors because it used larger amounts of energy. The AEV only traversed half of the track. This was due to the inconsistency of battery power, and track conditions. The group generated an input power and propulsion efficiency versus time graph. The AEV used very little amounts of power due to the coasting method.

Figure A4: Input Power & Propulsion Efficiency versus time for second test

The third test involved making the AEV more efficient, and less costly. The group added a servo to the AEV, the servo would functioned as a mechanical brake. The AEV became less efficient, but more reliable. The group also modified the design of the AEV. In order to connect to the caboose easier, the T shaped base plate now bolts directly to the L shaped bracket. This made the AEV sturdier, and allowed for a better placement for the metal coupler. The AEV was able to completely traverse the track. The graph of supplied power versus Time can be seen in Figure A5 on the next page. The most energy used was from pulling the caboose in reverse. This was due to an increase in input power, and from the extra weight of the caboose. The AEV moved well on the track, it appeared to still be a little off balance.

Figure A5: Graph of Supplied Power (Watts) vs. Time (s) for test 3

The group also modified the code. The group changed the units measuring distance back to marks. Initially the group used feet for convenience. This proved to be problematic, so the group changed the code back to marks. This allowed for a more precise way of measuring distance.

During the final test, the AEV stopped short of two of the gates twice. The AEV was within an inch of the gate sensor though. But with the assistance during those two instances the AEV completed the course. The final design of the AEV can be seen in Figure A11 which is located in the appendix. The final design weighed 0.254 Kg and had an energy to mass ratio of 1223.62 Joules per kilogram. The graph of supplied power and propulsion efficiency versus time is located in Figure A8, which is located in the appendix. Pulling the caboose required the greatest amounts of input power, and took a greater amount of time to move from station to station. During the run the AEV moved and stopped well, the AEV was still a little of balance. But it accelerated well, managed to complete the run. A table of the incremental energy per phase can be viewed in Table T2 located in the appendix. The phase that used the most energy was phase 10. This was when the AEV left the third station with the caboose. The phase only lasted for 8 seconds, but managed to use 83 joules during that time frame. After that phase the input power decreased to save energy until the AEV reached the gate.

Discussion

The first design used both a pusher and puller configuration. Both of the propellers were the bigger 3 inch ones. This was due to the system efficiency versus advance ratio graph located in Figure A3, located on the previous page. The 3 inch propeller could achieve a higher efficiency than the smaller propeller. The though was it might be able to pull the caboose easier. It used a minimal amounts of parts, it wasn’t balanced. It often hung to one side, when placed onto the track. The design did not accelerate well, it was probably due to the aerodynamics of the design. The design can be seen in Figure A6 located in the appendix. The second design used a pusher design, with the 3 inch propellers. It was better balanced, and accelerated faster, than the first design. Since the second design completed its scenario faster, it used less energy. So the group decided to continue development with the second design. This design can be viewed in Figure A7, located in the appendix. During the third performance test the group modified the design. The base plate was bolted directly to the L shaped bracket, this made the design sturdier, and allowed for the AEV to hook up to the caboose easier. The final design can be viewed in Figure A11 located in the appendix.

The concept screening and scoring from lab 3 in located in Table T2, and T3 in the appendix. The final design was balanced better than the first two prototype designs. But it still hung slightly to the side. The design was relatively flat, so blockage was to a minimum. The center of gravity was located in between the two wheels, near the base of the AEV. This was good, the AEV always stayed on the track, and moved well. Every couple of labs, the servo would need adjusted, but everything else worked fine. The cost was more due to the addition of the servo, when compared to the first two designs. Some uneeded brackets were removed in an attempt to save cost, and weight. The AEV was moderate with efficiency. The servo allowed for the AEV to stop consistently, and save on power. Completely relying on coasting would be the most efficient route, but it proved to be inconsistent. So the final design is still comparable to the concepts that were ranked.

The code used for the final testing can be viewed in Figure A10. After adding commands for the servo, the group needed to change the measured units from feet to marks. The change in units allowed for a more precise travel distance. When the units were in feet, the AEV stopped inconsistently. After changing the units to marks, the stopping distance became more consistent. The group also added a servo to function as the brake. This allowed for a more efficient and better means of stopping. The group had noted during the first performance test that the reversing command used a large amount of energy. All of these changes were made to allow the AEV to complete the mission objective. The total energy used by the AEV can be viewed in Table T1 located in the appendix. The AEV used 310.4 Joules of energy to complete the mission objective during the final test. Table T1 also contains the energy phases. The phases involving the caboose used almost twice as much energy as the first half.

The AEV accelerated well through the first half of the final testing. Once the AEV hooked up to the caboose, the AEV began to accelerate slower. This was surprising because the group increased the input power to compensate. The AEV had an energy to mass ratio of 1223.62 joules per kilogram. Without knowing other group’s ratio, no conclusions on the efficiency can be made.

Conclusion and Recommendation

Through trial and error Group B came up with a design that was able to complete the mission objective in an efficient and effective manner. Several contributions helped achieve this: First, group B decided to have their AEV to coast to a stop. While sacrificing consistency, it made the design more efficient as there was no power used to stop the AEV. Second was the servo brake. This was a compromise by members of Group B. The decrease in consistency was found to be too much, so members needed a way to increase reliability of the AEV. The servo brake did not use as much power as a reverse in the motors would have and it allowed the AEV to stop in the same position multiple times over. Third, group members came up with a function that allowed them to compute distances the AEV would travel in feet instead of marks, however this was found to be a bad choice. When trying to change the code a very small amount of distance it was found that changing 1 or 2 marks was much better than changing 0.1 ft. Group members realized that using feet was too large a scale with which to code small distances. When the AEV was just a few marks off of its destination, changing the code by just 0.1 feet changed the code by around 2.5 marks, instead of just 1 mark. As well, using an integer number of marks was better than using a decimal number of feet. Last was the decision to rotate the AEV. The AEV was not balanced well on the track and would wobble when going around the turns which increased friction with the wheels. This was detrimental to the overall efficiency of the AEV. As well, the bracket that was supposed to connect to the caboose magnet was found to be lower than the caboose magnet. Group members found that rotating the AEV would solve both of those problems. The different orientation of the AEV made it so that the weight hung directly under the track and not off to the sides.

Through making these changes the group designed an AEV that completed the objective in an efficient manner. As well, the techniques used to increase efficiency of the AEV on a small scale can be used in the real world with the same degree of success.

Appendix