Autodesk's VEX® Robotics Curriculum Unit 14: … Autodesk's VEX Robotics Unit 14: Accumulator Design Overview In Unit 14: Accumulator Design, you learn about the use and design of

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Autodesk's VEX® Robotics Curriculum

Unit 14: Accumulator Design

2 ■ Autodesk's VEX Robotics Unit 14: Accumulator Design

Overview

In Unit 14: Accumulator Design, you learn about the use and design of accumulators. You designyour own accumulator, report on your learning and findings, and speculate on design changes andimprovements given possible changes in the design challenge.

The concepts behind the accumulator design have many real-world applications. In STEMConnections, you are presented with the design of an automatic tennis ball collector. After completingthe Think Phase and Build Phase in Unit 14: Accumulator Design, you will see how those conceptscome 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:

Term

Definition

Accumulator A robot mechanism designed to pick up a large number of similar objects.

Autodesk®DesignReview (ADR)

Enables everyone in the design review team to view, print, measure, mark up, andrevise 2D and 3D designs without the original design creation software such asAutodesk® Inventor®.

Conveyance Something that carries objects up from an intake into a storage chamber.

Overview ■ 3

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 wellas in the Microsoft Vista operating system.

Elasticity Property enabling some objects/systems to overcome deformation and regainoriginal 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: AccumulatorDesign > Build Phase

One of the drivetrains built in Unit 9: DrivetrainDesign 1 > Build Phase or Unit 10: DrivetrainDesign 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


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.

Overview ■ 5

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.


Think Phase

Overview

This phase describes characteristics of accumulators. It covers important considerations foraccumulator 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.


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


The following supplies are used in this phase:

Supplies

Notebook and pen

Work surface

Think Phase ■ 7

Research and Activity

An accumulator is a robot mechanism designed to pick up a large number of similar objects. Thesemechanisms commonly utilize conveyor belts and rollers for their intake. The best accumulators havethe 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


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 theintake 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 opposingsurface. This relatively simple setup requires only one conveyor belt. However, this setup has somedisadvantages. First, since the balls are rolling, they move through the accumulator at half the speedof the conveyor belt. Second, this setup is subject to jamming if two balls are picked up too closelytogether and they touch inside the conveyor. Because the back side of the ball in front is moving upwhile the front side of the ball in back is moving down, the balls can bind up and jam.

Think Phase ■ 9

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 asingle belt adds significant complexity.

This is the best of the setups. With two belts, the balls no longer roll, but move straight up theconveyor. 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 sothat it pulls an object in faster than the drivetrain at maximum speed. In a single-belt system, thismeans that the intake is geared in such a way that the linear belt speed is more than double thedrivetrain's top speed. In a two-belt system, the intake's linear belt speed only needs to be more thanthe drivetrain's top speed. When it comes to accumulator gearing, faster is almost always better – justmake sure the accumulator can overcome the friction caused by pulling in the objects.


Compression and Elasticity

As explained in Unit 8: Friction and Traction, friction is applied between two surfaces held together bynormal force. For belts or rollers to pull in an object, there must be some force pressing the belt ontothe object.

Often this force is caused by the compression or elasticity of some part of the system. Sometimes theconveyor belting bends backwards and this “spring” is what applies the force on the object. Othertimes, the object itself has some elasticity and deforms when it is sucked into the intake. And yetother times, additional elastic bands or springs are used to give the entire conveyor assembly somegive, which enables it to deform when an object moves through it. In this case, the springs apply thenormal 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:

Think Phase ■ 11


Create Phase ■ 13

Create Phase

Overview

In this phase, you learn how to create and review a DWF file.

The completed exercise

Objectives


■ 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.


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 anobject fits into the larger model.


The following software is used in this phase:

Software

Autodesk Inventor Professional 2011

Create Phase ■ 15

Exercise: Create and Review a DWF File In this exercise, you create a Design Web Format(DWF) file for distribution to the design team. Youthen review a markup file with a note on modifyingthe depth of the tire tread.

The completed exercise

Create a DWF File The design team has a number of employees who areresponsible for manufacturing the parts. They do nothave access to Autodesk Inventor, so you will create aDesign Web Format (DWF) file for distribution to thedesign team. Note: Before you start this exercise, make surethat Autodesk® Design Review is installed on yourcomputer. 1. Make IFI_Unit14.ipj the active project. 2.

Open MicroController.iam.

3.

On the application menu, click Export > Exportto DWF. Note that the Enable Markups and theAllow Editing and Deletion of Markups checkboxes are selected.

4.

If required, select the Display Published Filein Viewer check box to open Autodesk DesignReview when the file is created.

5. Under Default Output Location of DWF File,

navigate to the Unit 14 folder containing thedatasets.

6. Click OK. 7. Click Publish to generate the DWF file.


8.

Click Save. The DWF file is displayed in Autodesk DesignReview. Depending on the speed of yourcomputer, 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 asshown.

13.

Move the cursor over the sphere on the tripod.Click the sphere and drag the part away fromthe assembly.

Using this workflow, you can take apart anassembly 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. In Autodesk Design Review, open

MicroController_Markup.dwfx. 2.

Review the Markups palette. The commentcreated by a member of the design team islisted. The symbol beside Change Part Color toGray (Dark) (1) indicates that the markup is ForReview.

In a typical workflow, you would now open theassembly and change the color of the part. Forthe purpose of this exercise, assume that theassembly is updated.

Create Phase ■ 17

3.

Click the padlock symbol to toggle off LockMarkup. (1)

4.

On the Markups tab, from the Status drop-down list, select Done.

The Markup palette changes to reflect thestatus of the markup. In the graphics window,the color of the text box changes.

5. Save the file.

Using the Send command, you can notify thedesign team by email that the assembly isupdated and that the DWF file reflects thechange.

6. Exit Autodesk Design Review.


Build Phase

Overview

In this phase, you design and build an accumulator to pick and hold ten ping pong balls.

Phase Objectives


■ Design and build an accumulator.


Before starting this phase, you must have completed:

■ Unit 14: Accumulator Design > Think Phase.


■ 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



Supplies

VEX Classroom Lab Kit

One of the drivetrains built in Unit 9: Drivetrain Design 1 > Build Phase or Unit 10: Drivetrain Design2 > Build Phase

Notebook and pen

Work surface

Build Phase ■ 19

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 mountthe 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 tenping pong balls. An example is shown.

When designing your accumulator, you will need to consider many factors, some of whichinclude:


■ 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 ofAutodesk Inventor software to explore potential solutions through the creation and testing ofdigital prototypes. Note: Come to class prepared to build and test your best ideas! Team members can download afree version of Autodesk Inventor Professional software to use at home by joining the AutodeskEducation Community today at www.autodesk.com/edcommunity.

2. Based on your criteria, choose a design and start building! 3. Once your accumulator is complete, hook it up to a Microcontroller and test the functionality.

Make improvements as you see fit. 4. 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 wantto attach the accumulator to the drivetrain so that it is able to complete this task as quickly aspossible.

5. 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. 6. Move on to the Amaze Phase and get ready for your upcoming challenge!

Amaze Phase ■ 21

Amaze Phase

Overview

In this phase, you use your robot from the previous Unit 14: Accumulator > Build Phase to pick up arow of ten ping pong balls as quickly as possible.

Phase Objectives


■ Explain the intricacies behind accumulator design. ■ Improve an accumulator based on test results.


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.


■ 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



Supplies

VEX Classroom Lab Kit

The robot built in the Unit 14: Accumulator Design > Build Phase

Notebook and pen

Work surface


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. Set up a row (or column) of ping pong balls on the floor. 2.

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. 4. Repeat the challenge a few times in an attempt to complete it as quickly as possible. Record all

your times in your engineering notebook.

Amaze Phase ■ 23

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 thatwere three times as heavy.


STEM Connections

Background

You have been asked to develop designs for a robotic tennis ball collector that incorporates yourknowledge 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 forcollection 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 atennis 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 objectcriteria: shape, size, weight, fragility, and surface texture?

2. Consider also which type of accumulator would maximize the collection speed for each type ofobject.

STEM Connections ■ 25

Math

Suppose you are testing the robotic tennis ball collector. Beginning two feet from the robot's startingposition, a ball is placed every three inches. You run several trials with five balls, and your accumulatorpicks them up and puts them into a hopper in an average time of 8.1 seconds per trial. Then, you runseveral trials with 10 balls, and your accumulator picks them up and puts them into the hopper inan average time of 11.3 seconds per trial. (If your accumulator is working, feel free to run the trialsyourself, 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?)

Documents

Autodesk's VEX® Robotics Curriculum Unit 14: … Autodesk's VEX Robotics Unit 14: Accumulator Design Overview In Unit 14: Accumulator Design, you learn about the use and design of