Teacher/Mentor Institute

Robot Design and Construction Tips

Scott McEwen

September 15, 2012

Overview

Engineering Design Process Subsystems & System Integration Communication & Documentation Design Engineering & Math Examples Construction Tips

Materials Fabrication & Safety

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Engineering Design ProcessImportance

Proven process for any design/build project

Every team is required to submit an engineering notebook that documents the process to design, build, and test your robot

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Engineering Design ProcessElements

1. Define the problem2. Determine the design

specifications3. Develop numerous design

alternatives4. Choose the optimal design5. Build and test the design

Ref:  http://best.eng.auburn.edu/ -> Participants -> Contest Information -> Team Resources -> Engineering Topics

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1) Define the Problem

Read the Rules thoroughly at www.bestinc.org The Competition -> Current Game Rules Participants -> File Manager -> Public

Files Participants -> Contest Information Password: r1bb0n

Inventory Consumable & Returnable Kits

Research similar problems and designs

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2) Determine the Design Specs

Clear guidelines for creating viable designs: Goals

Score lots of low point items, then score high point items

Requirements Ability to ascend/descend quickly Ability to grab various game pieces

Constraints Must fit in 24” cube and weigh <= 24

lbsPage 6September 15, 2012

3) Develop Numerous Design Alternatives

Engineering design = creative process + content knowledge from variety of disciplines

Brainstorming Multiple Groups of 3-4? 1+

designs/student? Sketches, notes, logical & physical

models Scoring Tip: Brainstorming

Approaches: How well organized and productive was the brainstorming approach used and documented?

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4) Choose the Optimal Design

Weigh and document pros & cons of each design Analysis of gaming strategies and

design elements to achieve goals Do we have the tools and skills to build

it? Scoring Tip: Analytical Evaluation of

Design Alternatives: Use of analytical and mathematical skills in deciding upon and implementing design alternatives

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5) Build and Test the Design

Invest adequate time and specificity prior to this step

Revisit prior design steps as needed Scoring Tip: Safety Training *and*

safety practices followed Scoring Tip: Support Documentation

Drawings, photos, test results, etc.

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Subsystems & System Integration

Drive Platform Ascend & descend Speed & position control

Articulated Arm and end effector (grapple) Rotate left to right Extend up & down Extend in & out Grip efficiently

ProgrammingPage 10September 15, 2012

Communication & Documentation

Communication Best Practices

Communication mediums Traditional Social media SCRUM – Daily stand-up meetings Other

Resolving disagreements/conflicts What works for your team?

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Communication & Documentation

Engineering Notebook Document the process used to

design, build, and test the robot. Tell the story of your robot

Documentation is a critical aspect of the Engineering Process. Provides: Crucial record of the process Critical info between different groups Checklist against requirements Essential information for new people

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Communication & DocumentationImportant Dates

Engineering Notebooks are due on Practice Day (Saturday, Oct 20)

Every team MUST submit an Engineering Notebook

If no notebook on Practice Day, your team will NOT be able to compete on Game Day

Notebooks will be returned on Game Day

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Design Engineering & MathExamples – Torque

Dimensions and torque Small Motor

http://content.vexrobotics.com/docs/276-1610-Drawing-Rev1A.pdf

Large Motor http://content.vexrobotics.com/docs/276-1611-Drawing-Rev1A.

pdf

Inch-pounds = amount of torque required to lift a 1 pound weight 1 that is 1 inch from axis of rotation

Computing torque: Torque = Force * Moment Arm Torque = Weight (pounds) * moment arm (inches) Total torque = Sum of (weights * moment arms)

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Design Engineering & Math Examples – Torque

PVC Pipe @ 0.21 lb/ft Grapple @ 0.5 lb Waste Cargo Ball @ 0.4 lb

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Design Engineering & Math Examples – Torque

PVC: (2 ft * 0.21 lb/ft) * 1 ft = 0.42 ft-lb

Grapple: 0.5 lb * 2 ft = 1.00 ft-lb

Ball: 0.4 lb * 2 ft = 0.80 ft-lb

Combined: 0.42 + 1.0 + 0.8 = 2.22 ft-lbs

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Torque = Weight (pounds) * moment arm (inches)

Design Engineering & Math Examples – Torque

2.22 ft-lbs = 26.64 in-lbs Large Motor torque = 23.53 in-lbs “Back to the drawing board”

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Design Engineering & Math Examples – Motor Specs

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Futaba S3003 servo• Torque: 2.75 in-lb (44 oz-in)• Gear Type: Plastic

BEST Small Motor• Torque: 9.49 in-lb (152 oz-in)

BEST Large Motor• Torque: 23.53 in-lb (376.48 oz-in)

Design Engineering & Math Examples – Potentiometer

(Pot) Definition. A Pot is an electrical device whose resistance is

adjustable. It can be used as an analog sensor to measure angular position of a rotational component, such as a robot arm. The Cortex can use the Pot’s output to control or limit some other component.

Input. Connect Pot’s shaft to a rotational axle or shaft. NOTE: the POT’s total range of motion (i.e., rotation) is 300 degrees.

Output. Connect the Pot’s wiring to a Cortex analog input port.

Operation. As the resistance of the Pot changes, so does the voltage. This varying voltage can be measured by the Cortex and is directly proportional to the angular position of the Pot’s shaft.

Data sheet: http://www.bitechnologies.com/pdfs/p160.pdf

easyC example: https://sites.google.com/site/team3141rx/easyc/arm3

Wiring example: http://www.education.rec.ri.cmu.edu/classes/cal_u/ar/toolbox/content/curriculum/robotics_systems/home_brew/potentiometer/potentiometer.swf

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Construction Tips

Materials Fabrication & Safety

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Materials

Polypropylene Sheet Aluminum bar, rod, & sheet Steel all-thread rod Wood PVC pipe Electrical Fasteners Miscellaneous

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Fabrication & SafetyClub Workshop

Location & Hours 999 Vallejo Street, east of I-25 and north of 8th Ave 7 days/week, 9a to 11p M-F; 8a to 11p, Sat & Sun

Cost: Special RM BEST rate Call 720-324-7222 for details

Tools Woodwork Shop, with CNC router Machine Shop Metal Shop

Classes www.clubworkshop.com

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Fabrication & SafetyCutting Plastic Sheet (video)

Wear eye protection & secure work1. Scribe and break – Sturdy knife

Good for 1/8” sheet

2. Jig saw – New blade, 10 teeth/inch3. Band saw – ½-wide blade, 14 teeth/inch

May cause melting

4. Circular saw – Carbide tip, triple-chip Plywood blade will cause melting

5. Table saw – 60-80 teeth, triple-chip, 1/8 to ½ inch blade exposed

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Fabrication & SafetyCutting Aluminum Bar &

RodWear eye protection & secure work ½-inch Bar

Hacksaw: laborious and slow Jig saw: (see notes) Band saw: wood-cutting blade Horizontal band saw:

straight & safe Visit Club Workshop

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Fabrication & SafetyCutting Aluminum Sheet

Tin Snips: laborious Stop short of full cut to

avoid cut marks Air or power shears Sheet metal shear

Visit Club Workshop

For marking, use ultrafine Sharpie

After cutting, dress edges with file

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Fabrication & SafetyBending Aluminum Sheet

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• Hand bender• Vise• Sheet metal brake

• Visit Club Workshop

Fabrication & SafetyPVC and Wood

PVC Hacksaw PVC cutter

Wood: Holes & round parts Drill Drill press Hole saw

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Fabrication & SafetyDrill Press Speeds (rpm)

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Bit Type Plywood& Pine

Acrylic Aluminum

Steel

Twist, 1/16” to 3/16” 3000 2500 3000 3000

Twist, 1/4” to 3/8” 3000 2000 2500 1000

Twist, 7/16” to 5/8” 1500 1500 1500 600

Twist, 11/16” to 1” 750 NR 1000 350

Hole Saw, 1” to 2.5” 500 NR 250 NR

Spade bit w/ spurs, 3/8” to 1”

2000 500 NR NR

Circle Cutter, 1.5” to 3” 500 250 NR NR

Circle Cutter, 3.25 to 6” 250 250 NR NR

Circle cutters: Drill 1st side, flip material over, finish on 2nd side

Wear eye protection & secure work

Fabrication & Safety

Wear eye protection & secure work Center punch holes to prevent drill

from wandering

Clamp work

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Fabrication & SafetyFasteners – Drill and Tap

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Machine Screw

Drill Bit Number

1/4”-20 8

#10-32 21

#8-32 29

• Threads are cut inside a hole using a tap

• Match hole size (numbered drill bit) to screw

• Screws: size – threads/inch• Purchase drill/tap sets at Ace

Hardware

Fabrication & SafetyElectrical Components

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Proper connection of electrical components

Mount Cortex for easy access

Fabrication & SafetyLimit Switches

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Mini Snap SubMini Snap

Connect to digital portClosed = “0”Open = “1”

Fabrication & SafetyVEX Motor Mounting Kit

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• Specifically designed to mount BEST motors

• Flat, but designed to be easily bent

Fabrication & SafetyBEST References

http://best.eng.auburn.edu/b_game_rules.php http://best.eng.auburn.edu/stored_procedures/folder-manager/

1. 2012 BEST Consumable Kit List2. 2012 BEST Returnable Kit List3. BEST Large Motor Spec Sheet4. BEST Small Motor Spec Sheet5. BEST Generic Kit Usage Guide6. 3.X VEXnet Firmware Upgrade Utility Operating Instructions and

Installation

7. Cortex Microcontroller and VEXnet Joystick User Guide

8. VEX Cortex Pin-out9. Introduction to easyC & Cortex (Intelitek)10. Google for PDF: “Tools, Tips and Materials” by David

Kwast

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Club Workshop

Location & Hours 999 Vallejo Street, east of I-25 and north of 8th Ave 7 days/week, 9a to 11p M-F; 8a to 11p, Sat & Sun

Cost: Special RM BEST rate Call 720-324-7222 for details

Tools Woodwork Shop, with CNC router Machine Shop Metal Shop

Classes www.clubworkshop.com

Page 36September 15, 2012