Mae3 robot analysis
- 1. MAE3 ROBOT ANALYSIS TEAM 37 The Championship Belt ZIYAN CUI(PERCY) SECTION A07 Julie Yu
- 2. Cui 1 Part I-Description: Complete Machine- The Championship Belt The robot we built for the MAE3 robot contest was a rail-based robot that moves at a set elevation with movable subframe, an extendable arm and a conveyor belt. The 3D CAD of the complete robot showed what our robot looks like at its starting position. The robot is break down into four task modules that were designed separately, which are the conveyor belt, robot arm, sub chassis and the main chassis. The main chassis consist of drivetrain that is powered by a GM-2 motor and moves along the rail. L-shape sub-rails and another GM-2 motor are fixed under the main chassis. The sub-chassis, which holds the arm and conveyor belt together, sits on the sub-rails and drives the gear rack on top to move the subframe along the sub-rails. The arm is integrated with gear rack on top and is controlled by a GM-9 motor so that it could move back and forth to grab the blocks. And at the bottom of the robot is the conveyor belt, supported by three 3D printed cylinders and powered by GM-9 motor, which is used to transport blocks across the table to the scoring area. The way in which the Championship Belt works is indicated by the two pictures below. mainchassisto move alone rails Rollersthatdrive the conveyorbelt Extendable arm Railsthat would allowthe subframe to move
- 3. Cui 2 Component- Extendable Arm This report will focus on the arm part of the design. The side holders on both sides have slot in the middle that would allow a 4-32 screw move freely inside. The actual arm is integrated with the gear rack, and with 4-32 screws at the end on both sides moving in the slots, so that the arm won’t tilt when it’s extended. The lower arm ensures the arm could pull two rows of blocks at the same time. Also, a GM-9 geared motor and a 12-pitch gear is included, and a motor mount bent from a single piece of sheet metal. Everything except the motor and its mount are made from the quarter-inch-thick acrylic board and are laser cut. Minimum Set of Functional Requirement The lower arm must be able to secure two rows of block at the same time The arm must have enough reach to go behind the blocks on the shelf The arm must have enough pulling force to pull back at least six blocks The lower arm can secure two rows and the motor could provide enough pulling forces that could even pull over forty blocks, which will be discussed later in the component analysis section. GM9 motor Lowerarm Arm integrated withrack Side holder Slotsthat allow 4-32 screwsto move
- 4. Cui 3 Part II- Project Management Prioritization and scheduling When the team first got the task at week 4, we all agreed not to rush ourselves to designing sophisticated parts. We want to have a clear image on how we are going to achieve our goal, which is score as much point possible easily within only one minute. Because we both agreed that when everyone of us know exactly what we are going to do could ensure the efficiency in future works, and it turns by spending more time conceptualizing our design intent the entire group didn’t run into trouble when assigning tasks relating to different task modules. The initial schedule was to finish the design by the end of week 7 and at the same time start our producing in week7 after we finish all our designs. With the help of the Pugh chart and the brainstorming in the first three meetings, we managed to finalize all the ideas and had a very rough hand sketch outline of our robot. As we initially scheduled, we started designing in Inventor from the middle of week 5, each group member had one of the four task modules assigned. We did not intentionally prioritize any design over others but in fact there are differences in the complexity of designing different parts. It was at that time we realized that there could start producing our part while someone still do the designs, not to mention that we still need to improve our design as the project proceeds. The arm part comes out at first, and we made it out in week6. Also, by doing the risk reduction in section on week6, we discovered some significant design flaws, even though we worked our way through it quickly we still decided to push forward the design and producing of another high-risk part of our design, the conveyor belt. And as it turned out the initial design couldn’t hold up together that we need some extra time fixing it. At those difficult moment we did not panic but took a little break to summarize everything we had done so far and redid the Gantt chart. We pushed the date when we want a fully functional robot forward by shorten the time to produce the low risk parts. Task assignment went into more details like who is going to bring what kind of file or what material should be ready before group meeting. The updated Gantt chart indeed greatly boosted the efficiency of the producing process and helped everyone to get more involved in the robot project as a whole rather than the part they designed. Throughout the entire project, time management has been a great challenge to the team. Looking back to all those Gantt chart and chats sent through the group members, I found out we manage to overcome the difficulties by doing the followings: always plan things out before we act, working together as a team to have the problem solved by the most suitable member and, most of all, never let the frustration overwhelms our passions about the robot project.
- 5. Cui 4 Part III-Analysis of Component Objectives As the only part that directly interact with the blocks sitting on the shelves, the viability and the performance of the extending arm directly determines the overall scoring potential of the entire robot. The objective of the analysis is to predict the maximum pulling force measured from the end of the lower arm. By getting the maximum pulling force we will be able to determine if the arm could pull six blocks off the shelf and onto the conveyor belt at once and whether we need to vary the rest of the design. FBD Inputmotor andgear Gear rack In here we analyze the armat its maximumextension,inorderto maximize the impactof the moment createdby the massof the arm itself
- 6. Cui 5 Force/Torque Analysis Assumptions Quasi-static All parts are rigid Mass are concentrated at one point as shown in the FBD Robots has no acceleration There’s no slipping in the gears and between gear racks The height of gear rack is considered negligible Equation involved ∑ Fx = Fapplied − Fpull − f = 0 ∑ Fy = N − G − Fgear = 0 ∑ M =N ∗ d3 − Fpull ∗ d2 − G ∗ d1 = 0 G = m ∗ g f = N ∗ µscrew Frequired = n ∗ m ∗ g ∗ µblock Analysis and Data As it is indicated in the free body diagram in the previous section, the GM-9 motor is the only power input in the entire system, and from the part list we find out: Ʈ = 0.25Nm And by measuring in the design studio, some data are given as: m = 105 grams µscrew = 0.2 Fapplied = Ʈ rgear = 0.25Nm 0.584in = 16.85N
- 7. Cui 6 d1 = 9.069inch − 0.5inch − 2.33cm = 19.44cm d2 = 1.5inch + 0.25inch = 4.45cm d3 = 0.5inch = 1.27cm Plug the values back into the equilibrium function, we get the set of equations with unknowns, Fpull, N, Fgear ∑ Fx = 16.85N − Fpull − 0.2N = 0 ∑ Fy = N − 1.03N − Fgear = 0 ∑ M =N ∗ 1.27cm − Fpull ∗ 4.45cm − 1.03 ∗ 19.44cm = 0 And by solving the equation we get Fpull = 8.1N, N = 44.0N, Fgear = 43.0N
- 8. Cui 7 The block we use in the robot contest weighs 32grams each, and the estimated coefficient of friction between the blocks and the top surface of the shelf is 0.32, and the design intend for the robot arm is to pull 6 blocks at the same time, thus the required force should be: Frequired = n ∗ m ∗ g ∗ µblock = 6 ∗ 32g ∗ 9.81N kg ∗ 0.32 = 0.60N ntheory = 8.1N 1N = 81 F. S. Force = Fpulling Freqiured = 8.1N 0.60N = 13.5 By testing the pulling force of the arm, I fixed a newton meter and turned on the fully extended arm to pull against the newton meter, and the measure pulling force was 9.5 Newton. Percent 𝐸𝑟𝑟𝑜𝑟 = Factual − 𝐹pull Factual ∗ 100% = 14.74% Force/Torque Conclusion To quantify the maximum pulling force, we could express the maximum pulling force in how much blocks the arm could move at the same time, which is 81 blocks, compared with the expected 6 blocks, the pulling force was more than enough.
- 9. Cui 8 Speed Analysisusing power Objectives To remove as much blocks from the shelf in the given contest time, we want the extending arm to move from its initial position to its maximum extension in three seconds. Assumptions There is no energy lose inside the system Heat generated from friction is neglected There is no slipping in the gear or the gear racks Mass of the gear is too small, so the moment of inertia of the gear is neglected The motor accelerates quickly and time required to reach maximum output is neglected Equations involved E = 1 2 ∗ m ∗ v2 P = 1 2 ∗ Ʈstall ∗ 1 2 ∗ ωno−load mtotal = mrack + mblcok ∗ n vrequired = 𝑙 𝑟𝑎𝑐𝑘 𝑡 𝑟𝑒quired Analysis and Data For GM-9 motor: Ʈ𝑠𝑡𝑎𝑙𝑙 = 0.25𝑁𝑚 ω 𝑛𝑜−𝑙𝑜𝑎𝑑 = 74𝑅𝑃𝑀 𝑚rack = 105𝑔𝑟𝑎𝑚 mblock = 32gram n = 6 lrack = 9.069inch trequired = 3s 𝑚 𝑡𝑜𝑡𝑎𝑙 = 297𝑔 = 0.297𝑘𝑔 Since there is no energy loss, power in= power out
- 10. Cui 9 Plugging the values into the equations, we get the following 1 2 ∗ mtotal ∗ v2 = 1 4 ∗ Ʈ𝑠𝑡𝑎𝑙𝑙 ∗ ω 𝑛𝑜−𝑙𝑜𝑎𝑑 ∗ t Solve equations and we have: v = 3.13m/s vrequired = 0.076m/s F.S. speed = 40.83 ttheory = 0.073s tmeasured = 1.5s Speed Conclusions As it can be seen from the calculation results, there exists a significant discrepancy in time. In the energy analysis we assumed there’s no energy loss as well as slippering in motor and gears; however, when it comes to the real robot, the center hold of the gear doesn’t match perfectly with the shaft of the motor, not to mention we screwed in the gear with a washer to make sure the gear keeps rotating with the motor. Also, there’s considerable friction force between gear and gear rack. Which both cause great energy loss from the output of the motor. During our measurement, we also noticed the speed during the movement is inconsistent, mostly because of the error in assembling the parts cause the movement is not perfectly aligned or even hindered.
- 11. Cui 10 Part IV-Overall Conclusion The analysis of the component is meant to address the viability and performance of the design. As it turned out, both the force analysis and speed analysis give us two digits factor of safety, which means there are lots of redundancy in the initial design and all the expectations are met. By doing the analysis, it occurs to me that when trying to approach am real life problem, it’s important to determine which are the factors that won’t noticeably affect the outcome of the analysis. For instance, the height of the gear rack in the force analysis has minor effect on the calculation; but the friction forces and energy loss in the speed analysis caused a huge inconsistency in the timing of the movement of the arm. During the design and assemble of the robot, the entire robot was built part by part. And for sure it caused a lot of problems. If I got the chance to repeat the project, I will put everything in Inventor first and have them well constrained, therefore the precision of the final assembly would be a lot better, which ultimately will lead to smooth and controllable motion of the robot. Also, I would use uniform screw, gear and shaft sizes, so that everything will be interchangeable. Finally, I would create a list of materials to keep track of everything and prevent the waste of materials or unnecessary laser cut or so. The MAE3 robot contest is a fun and engaging project. Working together with teammates towards a common goal really taught me a lot about teamwork and design studio skills. All of us take pride in our robot since it does successfully meet all the design intents. In addition, our design follows the principle that we want to score as much with the simplest possible structure but greatest consistency in performance. As it turns out, the robot only has linear motions in certain degrees of freedom thus it won’t create unexpected inertia or rotational forces. The idea of building simple but steady structures really saved us a lot of time when testing the robot and piloting it during the competition. In conclusion, the robot is well-built and rigid; it has sufficient power to accomplish all the tasks. But also, the failure and frustration occurred during the project would also helped me to be a better engineer. With all that I’ve achieved in the robot project, I believe my next robot will definitely be a lot better.