Autodesk's VEX Robotics Curriculum Unit 14: Accumulator Design 1
Overview In Unit 14: Accumulator Design, you learn about the use and design of accumulators. You design your own accumulator, report on your learning and findings, and speculate on design changes and improvements given possible changes in the design challenge. The concepts behind the accumulator design have many real-world applications. In STEM Connections, you are presented with the design of an automatic tennis ball collector. After completing the Think Phase and Build Phase in Unit 14: Accumulator Design, you will see how those concepts come into play in the real world. Objectives After completing Unit 14: Accumulator Design, you will be able to: Describe the basic considerations of accumulator design and design a basic mechanism to collect multiples of an object off the floor. Create and review a DWF file using Autodesk Inventor Professional 2011 software. Apply the knowledge gained in the Unit 14: Accumulator Design > Think Phase to design and build an accumulator. Improve an accumulator based on test results. Prerequisites and Related Resources Related resources for Unit 14: Accumulator Design are: Unit 1: Introduction to VEX and Robotics Unit 2: Introduction to Autodesk Inventor Unit 4: Microcontroller and Transmitter Overview Unit 5: Speed, Power, Torque, and DC Motors Unit 6: Gears, Chains, and Sprockets Unit 7: Advanced Gears Unit 8: Friction and Traction Unit 12: Object Manipulation Key Terms and Definitions The following key terms are used in Unit 14: Accumulator Design: 2 Term Definition Accumulator A robot mechanism designed to pick up a large number of similar objects. Autodesk Design Review (ADR) Enables everyone in the design review team to view, print, measure, mark up, and revise 2D and 3D designs without the original design creation software such as Autodesk Inventor. Conveyance Something that carries objects up from an intake into a storage chamber. Autodesk's VEX Robotics Unit 14: Accumulator Design
Term Definition Compression The reduction in volume (causing an increase in pressure) of an object. DWF Abbreviation for the Design Web Format file type. DWFx A file extension for saving content to be viewed in Autodesk Design Review as well as in the Microsoft Vista operating system. Elasticity Property enabling some objects/systems to overcome deformation and regain original shape and size when externally applied balanced forces are removed. Intake Entrance area of an accumulator for robotic object gathering. Markup A single comment or a redline geometry correction inserted into a DWF file. Required Supplies and Software The following supplies and software are used in Unit 14: Accumulator Design: Supplies Software VEX Classroom Lab Kit Autodesk Inventor Professional 2011 The robot built in the Unit 14: Accumulator Design > Build Phase One of the drivetrains built in Unit 9: Drivetrain Design 1 > Build Phase or Unit 10: Drivetrain Design 2 > Build Phase Notebook and pen Work surface Small storage container for loose parts Ten ping pong balls 6 x 6 of open space One stopwatch Overview 3
Academic Standards The following national academic standards are supported in Unit 14: Accumulator Design. Phase Standard Think Science (NSES) Unifying Concepts and Processes: Form and Function Physical Science: Motions and Forces Science and Technology: Abilities of Technological Design Technology (ITEA) 5.8: The Attributes of Design Mathematics (NCTM) Algebra Standard: Understand patterns, relations, and functions. Communication: Communicate mathematical thinking coherently and clearly to peers, teachers, and others. Connections: Recognize and apply mathematics in contexts outside of mathematics. Create Science (NSES) Unifying Concepts and Processes: Form and Function Physical Science: Motions and Forces Science and Technology: Abilities of Technological Design Technology (ITEA) 5.8: The Attributes of Design 5.9: Engineering Design 6.12: Use and Maintain Technological Products and Systems Mathematics (NCTM) Numbers and Operations: Understand numbers, ways of representing numbers, relationships among numbers, and number systems. Algebra Standard: Understand patterns, relations, and functions. Geometry Standard: Use visualization, spatial reasoning, and geometric modeling to solve problems. Measurement Standard: Understand measurable attributes of objects and the units, systems, and processes of measurement. 4 Autodesk's VEX Robotics Unit 14: Accumulator Design
Phase Standard Build Science (NSES) Unifying Concepts and Processes: Form and Function Physical Science: Motions and Forces Science and Technology: Abilities of Technological Design Technology (ITEA) 5.8: The Attributes of Design 5.9: Engineering Design 6.11: Apply the Design Process Mathematics (NCTM) Algebra Standard: Understand patterns, relations, and functions. Geometry Standard: Use visualization, spatial reasoning, and geometric modeling to solve problems. Numbers and Operations: Compute fluently and make reasonable estimates. Measurement: Apply appropriate techniques, tools, and formulas to determine measurements. Connections: Recognize and apply mathematics in contexts outside of mathematics. Problem Solving: Solve problems that arise in mathematics and in other contexts. Problem Solving: Apply and adapt a variety of appropriate strategies to solve problems. Amaze Science (NSES) Unifying Concepts and Processes: Form and Function Physical Science: Motions and Forces Science and Technology: Abilities of Technological Design Technology (ITEA) 5.8: The Attributes of Design 5.9: Engineering Design 6.11: Apply the Design Process Mathematics (NCTM) Algebra Standard: Understand patterns, relations, and functions. Geometry Standard: Use visualization, spatial reasoning, and geometric modeling to solve problems. Numbers and Operations: Compute fluently and make reasonable estimates. Communication: Communicate mathematical thinking coherently and clearly to peers, teachers, and others. Connections: Recognize and apply mathematics in contexts outside of mathematics. Measurement: Apply appropriate techniques, tools, and formulas to determine measurements. Problem Solving: Solve problems that arise in mathematics and in other contexts. Problem Solving: Apply and adapt a variety of appropriate strategies to solve problems. Overview 5
Think Phase Overview This phase describes characteristics of accumulators. It covers important considerations for accumulator design. Phase Objectives After completing this phase, you will be able to: Design a basic mechanism to collect multiples of an object off the floor. Calculate the gearing necessary for an accumulator based on robot drivetrain speed. Describe the basic considerations of accumulator design. Prerequisites and Related Resources Related phase resources are: Unit 5: Speed, Power, Torque, and DC Motors Unit 6: Gears, Chains, and Sprockets Unit 8: Friction and Traction Unit 12: Object Manipulation Required Supplies and Software The following supplies are used in this phase: Supplies Notebook and pen Work surface 6 Autodesk's VEX Robotics Unit 14: Accumulator Design
Research and Activity An accumulator is a robot mechanism designed to pick up a large number of similar objects. These mechanisms commonly utilize conveyor belts and rollers for their intake. The best accumulators have the following characteristics: A wide intake mouth, enabling pickup without precise robot positioning. The means to prevent jamming of objects after pickup. A high-speed intake that enables a robot to suck up an object even at full speed. The ability to pick up multiple objects at the same time. The ability to pick up a large number of objects one after another without jamming or slowing down. The capability for picking up objects with size variances. Examples of accumulators are shown here: Accumulator built from VEX Intake Rollers and designed to pick up softballs Think Phase 7
Accumulator with a single roller to pull balls into a large tray A component common in many accumulators is a conveyance system that carries objects from the intake up into a storage chamber. One simple version of this is a conveyor belt in front of a flat wall. In this type of conveyor, the belt contacts the balls on one side and rolls them up the opposing surface. This relatively simple setup requires only one conveyor belt. However, this setup has some disadvantages. First, since the balls are rolling, they move through the accumulator at half the speed of the conveyor belt. Second, this setup is subject to jamming if two balls are picked up too closely together and they touch inside the conveyor. Because the back side of the ball in front is moving up while the front side of the ball in back is moving down, the balls can bind up and jam. 8 Autodesk's VEX Robotics Unit 14: Accumulator Design
A way around this jamming issue is to use independent rollers instead of one long conveyor belt. In this type of setup, each of the rollers is linked to the power source. This system is less likely to jam, but is still subject to many of the problems found in the first setup. Also, using many rollers instead of a single belt adds significant complexity. This is the best of the setups. With two belts, the balls no longer roll, but move straight up the conveyor. It is almost impossible for two objects to touch, and if they do, jamming is less likely to occur. One downside of this system is the added complexity of using two belts. Accumulator Gearing It is important to gear your accumulator appropriately. Ideally, the accumulator intake is geared so that it pulls an object in faster than the drivetrain at maximum speed. In a single-belt system, this means that the intake is geared in such a way that the linear belt speed is more than double the drivetrain's top speed. In a two-belt system, the intake's linear belt speed only needs to be more than the drivetrain's top speed. When it comes to accumulator gearing, faster is almost always better just make sure the accumulator can overcome the friction caused by pulling in the objects. Think Phase 9
Compression and Elasticity As explained in Unit 8: Friction and Traction, friction is applied between two surfaces held together by normal force. For belts or rollers to pull in an object, there must be some force pressing the belt onto the object. Often this force is caused by the compression or elasticity of some part of the system. Sometimes the conveyor belting bends backwards and this spring is what applies the force on the object. Other times, the object itself has some elasticity and deforms when it is sucked into the intake. And yet other times, additional elastic bands or springs are used to give the entire conveyor assembly some give, which enables it to deform when an object moves through it. In this case, the springs apply the normal force on the object. Finding the correct balance of grip on an object is sometimes difficult, especially when building an accumulator designed to pick up multiple objects at the same time. Example Accumulators Accumulators built using the VEX Robotics Design System are shown here: 10 Autodesk's VEX Robotics Unit 14: Accumulator Design
Think Phase 11
12 Autodesk's VEX Robotics Unit 14: Accumulator Design
Create Phase Overview In this phase, you learn how to create and review a DWF file. The completed exercise Objectives After completing this phase, you will be able to: Create and review a DWF file. Prerequisites Before starting this phase, you must have: A working knowledge of the Windows operating system. Completed Unit 1: Introduction to Vex and Robotics > Getting Started with Autodesk Inventor. Completed Unit 2: Introduction to Autodesk Inventor > Quick Start for Autodesk Inventor. Create Phase 13
Technical Overview The following Autodesk Inventor tools are used in this phase: Icon Name Description Move & Rotate Enables you to move and rotate 3D objects. By pulling a model apart, you can better view an object or see how an object fits into the larger model. Required Supplies and Software The following software is used in this phase: Software Autodesk Inventor Professional 2011 14 Autodesk's VEX Robotics Unit 14: Accumulator Design
Exercise: Create and Review a DWF File In this exercise, you create a Design Web Format (DWF) file for distribution to the design team. You then review a markup file with a note on modifying the depth of the tire tread. 3. On the application menu, click Export > Export to DWF. Note that the Enable Markups and the Allow Editing and Deletion of Markups check boxes are selected. 4. If required, select the Display Published File in Viewer check box to open Autodesk Design Review when the file is created. 5. Under Default Output Location of DWF File, navigate to the Unit 14 folder containing the datasets. Click OK. Click Publish to generate the DWF file. The completed exercise Create a DWF File The design team has a number of employees who are responsible for manufacturing the parts. They do not have access to Autodesk Inventor, so you will create a Design Web Format (DWF) file for distribution to the design team. Note: Before you start this exercise, make sure that Autodesk Design Review is installed on your computer. 1. 2. Make IFI_Unit14.ipj the active project. Open MicroController.iam. 6. 7. Create Phase 15
8. Click Save. The DWF file is displayed in Autodesk Design Review. Depending on the speed of your computer, this may take one to two minutes. 9. Autodesk Design Review uses standard viewport manipulation tools. Try the following: Hold down the left mouse button. Drag the mouse to rotate the model. Roll the mouse wheel to zoom in or out. Hold down the mouse wheel. Drag the mouse to pan the model. 10. On the ViewCube, click Home. 11. On the Tools tab, 3D Tools panel, click Move & Rotate. 12. Select the analog/digital connectors part as shown. 13. Move the cursor over the sphere on the tripod. Click the sphere and drag the part away from the assembly. Using this workflow, you can take apart an assembly for review. 14. Double-click the part to return it to its original position. 15. Press ESC to exit the command. Review a Markup 1. 2. In Autodesk Design Review, open MicroController_Markup.dwfx. Review the Markups palette. The comment created by a member of the design team is listed. The symbol beside Change Part Color to Gray (Dark) (1) indicates that the markup is For Review. In a typical workflow, you would now open the assembly and change the color of the part. For the purpose of this exercise, assume that the assembly is updated. 16 Autodesk's VEX Robotics Unit 14: Accumulator Design
3. Click the padlock symbol to toggle off Lock Markup. (1) 4. On the Markups tab, from the Status dropdown list, select Done. The Markup palette changes to reflect the status of the markup. In the graphics window, the color of the text box changes. 5. 6. Save the file. Using the Send command, you can notify the design team by email that the assembly is updated and that the DWF file reflects the change. Exit Autodesk Design Review. Create Phase 17
Build Phase Overview In this phase, you design and build an accumulator to pick and hold ten ping pong balls. Phase Objectives After completing this phase, you will be able to: Design and build an accumulator. Prerequisites and Related Resources Before starting this phase, you must have completed: Unit 14: Accumulator Design > Think Phase. Related phase resources are: Unit 1: Introduction to VEX and Robotics Unit 4: Microcontroller and Transmitter Overview Unit 5: Speed, Power, Torque, and DC Motors Unit 6: Gears, Chains, and Sprockets Unit 7: Advanced Gears Unit 8: Friction and Traction Unit 12: Object Manipulation Required Supplies and Software The following supplies are used in this phase: Supplies VEX Classroom Lab Kit One of the drivetrains built in Unit 9: Drivetrain Design 1 > Build Phase or Unit 10: Drivetrain Design 2 > Build Phase Notebook and pen Work surface 18 Autodesk's VEX Robotics Unit 14: Accumulator Design
Supplies Small storage container for loose parts Ten ping pong balls Optional: Autodesk Inventor Professional 2011 Activity Design and Build an Accumulator In this activity, you design and build an accumulator to pick up ten ping pong balls. You then mount the accumulator on a drivetrain of your choice. This robot will be used in the Amaze phase of Unit 14: Accumulator Design to pick up ten ping pong balls as quickly as possible. 1. In your notebook, brainstorm different types of accumulators that can pick up and store the ten ping pong balls. An example is shown. When designing your accumulator, you will need to consider many factors, some of which include: Build Phase 19
2. 3. 4. 5. 6. 20 What can be used at the intake of the accumulator? If a roller is used, how fast should it be geared? Should a conveyor be used? What material will grip the ball the best? How much storage space is needed? How will the accumulator be mounted on the drivetrain? Does it need an arm? How far from the ground should the accumulator be? How large should the opening of the accumulator be? Work as professionals in the engineering and design fields by leveraging the power of Autodesk Inventor software to explore potential solutions through the creation and testing of digital prototypes. Note: Come to class prepared to build and test your best ideas! Team members can download a free version of Autodesk Inventor Professional software to use at home by joining the Autodesk Education Community today at www.autodesk.com/edcommunity. Based on your criteria, choose a design and start building! Once your accumulator is complete, hook it up to a Microcontroller and test the functionality. Make improvements as you see fit. After you have tested the accumulator, mount it on your chosen drivetrain. Remember that in the upcoming challenge you will be driving this robot and picking up ping pong balls. You want to attach the accumulator to the drivetrain so that it is able to complete this task as quickly as possible. Plug in motors and servos to the appropriate ports in the Microcontroller. Test your arm with a transmitter to make sure everything is functioning correctly. Move on to the Amaze Phase and get ready for your upcoming challenge! Autodesk's VEX Robotics Unit 14: Accumulator Design
Amaze Phase Overview In this phase, you use your robot from the previous Unit 14: Accumulator > Build Phase to pick up a row of ten ping pong balls as quickly as possible. Phase Objectives After completing this phase, you will be able to: Explain the intricacies behind accumulator design. Improve an accumulator based on test results. Prerequisites and Related Resources Before starting this phase, you must have: Completed Unit 1 Accumulator Design > Think Phase. Completed Unit 1 Accumulator Design > Think Phase. An assembled Accumulator from the Unit 14: Accumulator Design > Build Phase attached to a drivetrain of your choice. Related phase resources are: Unit 1: Introduction to VEX and Robotics Unit 4: Microcontroller and Transmitter Overview Unit 5: Speed, Power, Torque, and DC Motors Unit 6: Gears, Chains, and Sprockets Unit 7: Advanced Gears Unit 8: Friction and Traction Required Supplies and Software The following supplies are used in this phase: Supplies VEX Classroom Lab Kit The robot built in the Unit 14: Accumulator Design > Build Phase Notebook and pen Work surface Amaze Phase 21
Supplies 6 x 6 of open space Ten ping pong balls One stopwatch Evaluation Ping Pong Ball Challenge In this challenge, you attempt to pick up ten ping pong balls as quickly as possible. 1. 2. Set up a row (or column) of ping pong balls on the floor. Place your robot approximately 2' from the row of balls as shown. 3. Using your robot, pick up all ten ping pong balls as quickly as possible. Time from the start of your robot's motion to the point where the last ping pong ball has entered your robot. Repeat the challenge a few times in an attempt to complete it as quickly as possible. Record all your times in your engineering notebook. 4. 22 Autodesk's VEX Robotics Unit 14: Accumulator Design
Engineering Notebook Calculate your average time to complete the challenge. For each time, explain why it was faster or slower than the average. How would you improve your accumulator to pick up the balls faster? If you replaced the ping pong balls with an equal-sized ball, but three times as heavy, how would you have to change your design? If the ping pong balls were covered in oil, how would you change your design? Presentation Present your design to the class. Explain the changes you would make if you had to pick up balls that were three times as heavy. Amaze Phase 23
STEM Connections Background You have been asked to develop designs for a robotic tennis ball collector that incorporates your knowledge of accumulator design. Science A tennis ball is a sphere. What is it about the spherical nature of a tennis ball that makes it ideal for collection by an accumulator? 1. Consider the fuzzy surface of tennis balls and explain how this surface design might facilitate the collection of tennis balls in an accumulator. 2. What are the advantages and disadvantages of an accumulator designed to collect spheres? Technology An agricultural equipment inventor is brainstorming ideas for an accumulator mechanism similar to a tennis ball collector to collect walnuts that have fallen to the ground. How would this inventor have to change the tennis ball picker design in order to make a successful walnut accumulator? Engineering Two common accumulator designs are a continuous conveyor belt and a series of rollers. 1. Ideally, what type of objects are best suited to each design with respect to the following object criteria: shape, size, weight, fragility, and surface texture? 2. Consider also which type of accumulator would maximize the collection speed for each type of object. 24 Autodesk's VEX Robotics Unit 14: Accumulator Design
Math Suppose you are testing the robotic tennis ball collector. Beginning two feet from the robot's starting position, a ball is placed every three inches. You run several trials with five balls, and your accumulator picks them up and puts them into a hopper in an average time of 8.1 seconds per trial. Then, you run several trials with 10 balls, and your accumulator picks them up and puts them into the hopper in an average time of 11.3 seconds per trial. (If your accumulator is working, feel free to run the trials yourself, perhaps with ping pong balls, and use your times instead of these.) 1. Write a linear function to approximate the amount of time your accumulator will need to collect n balls. Use that function to predict how long it will take for your accumulator to grab 12 tennis balls. 2. What are some strengths and weaknesses of using this linear model? (If you ran trials with your own accumulator, how good was the prediction?) STEM Connections 25