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1 | P a g e The Engineering Design Process-Vex Robotics Team 4540B

Youthville DetroitVex Robotics Team 4540B

Engineering Design Notebook2011-2012

Transformers (Autobots / Decepticons)


TABLE OF CONTENTS

TEAM BIOGRAPHIES

DIAMOND HOWARDSHERRELL HANEYDARRIEL DICK

MR. ELMER SANTOSMR. NARHU LAMPKINMR. LAMAR ADAMSMR. YANDAL WAUGH

DEFINING THE ENGINEERING PROBLEM

SOLUTIONINTAKE SYSTEM

Pinchy ClawBasket and Scoop

MAXIMUM ROBOT WEIGHTMAXIMUM ROBOT HEIGHTALLOWED CONTROL SYSTEMS

Allowed motorsRequired batteriesAllowed building material

ROBOTICS PROGRAM BUDGET OUTLINE

SPECIFICATION RANKING

GENERATE CONCEPT AND ALTERNATIVES

INITIAL ROBOT IDEA DRAWINGDRAWING OF ARM AND MOUNT

Claw Concept DrawingIntake System Concept

COMPLETED B ROBOTCOMPLETED D ROBOT

CHOOSE A CONCEPT

DETAILED DESIGN

PHYSICS EQUATIONSCOMPOUND GEAR ASSEMBLY FOR ARM

Gear ratio for Pinchy ClawDrive Train Base


INDEPENDENT WHEEL TORQUE:4-LINK DESIGN SYSTEMPROGRAMMING FOR EASYC: MOTOR MAPPING

Diamond Howard- Diamond is the Driver for team 4540. Diamond also programs in EasyC and can repair and modify the robot. Diamond has been and member of the Robotics team for 2 years


Sherrell Haney-Sheryl is the backup driver and Mechanical Design Engineer for team 4540. Sherrell is in charge of robot modifications, repairs and wiring. In addition, Sherrell can also program in EasyC.

Darriel Dick- Darriel is the Driver for team 4540. Darriel also programs in EasyC and can repair and modify the robot. Darriel has been and member of the Robotics team for 1 years.

Mr. Elmer Santos- Mr. Santos is the engineering mentor for Team 4540. His is a Mechanical Engineer and works for General Motors. A graduate of Sanford University he holds a Masters degree in his field. Mr. Santos mentors over 10 Vex Teams in the Metro Detroit Area. He also mentors over 15 FLL and LTU RoboFest robotics teams. He has been a robotics mentor for 15 years.

Mr. Lamar Adams- Mr. Adams is the Coach for Team 4540. He has been teaching robotics for 5 years. Mr. Adams also coaches LTU RoboFest teams and FIRST Lego League teams.


Mr. Nahru Lampkin- - Mr. Adams is the Coach for Team 4540. He has been teaching robotics for 5 years. Mr. Adams also coaches LTU RoboFest teams and FIRST Lego League teams.

Mr. Yandal Waugh- Mr. Waugh is the Coach for Team 4540. His is a former engineer with Motorola SPS and IBM’s ASIC Western Field Design Center where he worked as a VLSI engineer. He has been teaching robotics for 10 years. Mr. Waugh also coaches 4 LTU RoboFest teams and 6 FIRST Lego League teams.

Step 1- Define the Problem

What is the most effective strategy for playing the game? How do we win matches? How can the robot score the most points during the match? How do we score more than

our opponents? How can the robot pick up the game object? How can the robot pick it up quickly? How many game elements does the robot need to hold?


Solution:

In our meetings we talked about different approaches to take the elements and score both 1 at a time and multiple elements at a time. In addition, we talked about scoring offense and defense during the rounds. The ability to pre-load the 2 elements and autonomous scoring was thought out as well. Three different design types were finalized for prototyping and development:

Intake system- In this system there is a vertical take component that has soft roller gears to grab elements from their outer diameter and push them up the vertical metal component. The system would be put in reverse to feed the elements on the lower and upper goals.

Driver control for intake system- The system would have two drivers. One person would drive the base of the robot, and the other person would pick elements up and score.

Arm will use a 4-link system for execution.

Pinchy Claw- In this system the robot has a claw that can pick up elements by pinching the outside diameter of the elements. With this system the robot can pick up multiple elements stacks or 1 element at a time.

Driver control for intake system- The system would have two drivers. One person would drive the base of the robot, and the other person would pick elements up and score/de-score. There is an option for only 1 driver for this system as well.


Basket and scoop: in this system the robot is equipped with an intake system that scoops multiple elements into a basket that can expand to accommodate many elements. This robot is also design to be defensive.

Driver control for intake system- The system would have two drivers. One person would drive the base of the robot, and the other person would pick elements up and score/de-score.


Step 2- Generate Specifications

1. Design Constraints2. Functional Requirements

Maximum robot weight Maximum robot height Allowed control systems

Allowed motors Required batteries Allowed Build Materials

Must fall within designer’s budget Must be manufactured without complex machinery


Robot can run for 2 minutes continuously without draining its power supply Can hold 4-5 game elements at once Can drive at top speed for ½ m/s

Solution:

Maximum robot weight:

This may be important for several reasons. Because this year’s game allows pining for a limited amount of time, weight may be important so the robot will be harder to pin or tip over. Also, if we reach Nationals or the World Championships, the weight would affect our shipping cost for FedEx. We have limited funds so we have to be carful about the weight.

Maximum robot height:

The height and dimensions for the robot are the same as last year, 18 inches by 18 inches by 18 inches. All of the manipulators and other systems we develop have to stay within these specs at all times.

Allowed control systems:

Last year we used the R/C style controllers with crystals. At the nationals and Worlds everyone had to use VexNet systems. Because this years they switched over to the new X-Box style joystick systems, and the school set aside money for robotics equipment we decided to purchase the new equipment in hopes that we could use it for several years.

The old PIC Controllers were scrapped and the new Cortex controllers are being used this year. The new Cortex controllers have the VexNet system built-in and the new X-Box joysticks are easy to adapt to.

Updated software to new EasyC for Cortex. Also trying RobotC for the 1st time this year, we will decide on what the best language for our programming as the season goes on

Allowed motors:

Both 2 and 3 wire motors systems were available for use. In addition, this year there is a high powered motor option. Because the high powered motors were more expensive we choose to use the older 3-wire motors for this year’s design. Also to cut down on confusion, we are not using servo motors. Sometimes in the middle of a tournament people get nervous and my not read the side of the motor to see if it is a motor or servo. It has happened were some one has changed out a drive base motor and accidently replaced it with a servo and wondered what was wrong!


Required batteries:

All batteries used on the robot base are Nickel Cadmium with 3000mA. Last years the 7.2 Nickel Cadmiums were 2000mA. To make sure there would be no confusion with the batteries like someone trying to use the new chargers to charge an old battery or vise versa we got rid of all the old 2000mA NiCad’s. Also, for the new joysticks we are using rechargeable AAA batteries form Vex. The old square reachable batteries from last years R/C style remotes won’t work with the new equipment.

Allowed Build Materials:

All metal, axles, collars, bearings, screws, spacers, etc are all form Vex robotics only. None of the VexPro equipment can be used for Vex Robotics competition. In addition, any none Vex parts cannot be used for design of a competition robot.

Robotics Program Budget Outline:

Our school set aside $10,000.00 for the robotics program this year after the teams 2010 National Championship win. This expanded our program from 1 team to 4 teams that now serves 16 students. This materials list for 4 robots.

Item cost quantity totalStartup Cost (4 teams)RobotC Cortex site license (12 seat) (276-1740) $500.00 1 $500.00Programming Hardware Kit(276-2186) $49.99 4 $199.96


Booster Kit (276-2232) $179.99 8 $1,439.92Vex Claw Kit (276-2212) $19.99 4 $79.96Ext cables (276-1424) $39.99 8 $319.92Battery straps (276-2219) $4.99 4 $19.96Omni Wheels (276-2185) $24.99 16 $399.84Round Up Field Kit (276-1556) $499.00 1 $499.007.2v Robot battery (276-1491) $29.99 8 $239.92Vex robot battery charger (276-1445+276-1500) $19.99 4 $79.96Vex Cortex Bundle(276-1604) $399.99 4 $1,599.963-wire motor (276-2163) $19.99 44 $879.56Tool Kits(276-1645) $30.00 4 $120.00Safety Glasses(276-2175) $7.99 16 $127.84Robotic joystick (276-2192) $149.99 4 $599.96Medium Chassis Kit (275-1033) $21.35 4 $85.40Optical Encoder (276-2156) $19.99 8 $159.92Potentiometer (276-2216) $19.99 8 $159.92Ultrasonic Range Finder (276-2155) $19.99 8 $159.92Chain and Sprocket kit ( 276-2166) $29.99 8 $239.92

Adjusted Total $7,910.84

That’s $10,000.00-$7,910.84 = $2089.14 (Remaining Balance)

This was the amount used for Regional Tournament Fees, Registration Fees, and other associated cost.

Step 3- Specification Ranking

Use system to identify the importance of different elements of the robot performance.

W= Wish (not that important, but it would be nice if it is possible)

P= Preferred (important, but the project won’t fall without it)

D= Demand (critical to the project, MUST be included)

Robot can hold 1 game element- D


Robot can hold 2 game elements- P

Robot can hold 4-5 game elements- W

1. Robot can hold 1 game element- D2. Robot can hold 2 game elements- P3. Robot can hold 4-5 game elements- W4. Robot can score high goals-P5. Robot can score 1 element during autonomous period-D6. Robot can score 4 element during autonomous period-P7. Robot has multiple autonomous modes-P8. Robot can de-score multiple elements at a time-P9. Robot can de-score from the high goal-P10. Robot can move sideways/laterally-W11. Robot uses a ultrasonic sensor to see-P12. Robot uses an touch sensor to find stuff-P13. Robot uses Optical Encoders to keep straight during autonomous-W14. Robot uses Potentiometers to limit the range of the arm during autonomous-P15. Robot has a defensive autonomous mode-D16. Robot has 4 link arm system-D17. Robot has a basket-W18. Robot has protection from pining moves-D19. Robot can pin other robots effectively-D20. Robot has 4 wheel drive-D21. Robot has 6 wheel drive-W22. Robot has space for sponsor and donor recognition-W

Step 4-Generate Concepts and Alternatives

This is the imagination part of the process. Design robot design with pencil and paper to match up with previous design steps. Draw several design ideas and choose which the team thinks may offer the best competition design and most cost effective. Include pictures of sketches in engineering notebook presentation. Our team looked at several videos on YouTube over the summer of teams that were already designing and competing. We concluded that 2 designs were working the best from what we saw: 1) the claw, and 2) the intake systems. This was the inspiration for our final design. Smart engineer “observe” and “borrow” great working design, then improve upon them. That is exactly what we did!


Drawing of Arm assembly Concept

Step 5- Prototyping

This is the part where we bring our sketches to life by putting together chassis, manipulators, 4-link systems, support structures, etc. Include pictures of initial designs and basic prototyping.


Ariel Gray and Sheryl Haney work on their prototype

Team 4540B constructs the arm lift support for their modified robot design


Darriel takes control during a qualification match at the Cranbrook School tournament where we 1st tested our design.


Step 6- Choose a Concept

Comparison Criteria Weight

Cost 5Complexity 10Weight 5Tightness of Grip 5Required Drive Precision 15Speed of Grab 10Fast Arm Operation 10

Roller Intake BasketScore

Weighted Score

3 153 304 203 155 754 40

Roller Intake basket Total: 195

Pinchy ClawScore

Weighted Score

3 152 202 202 105 753 30

Pinchy Claw: 170

ScoopScore

Weighted Score

5 255 05 01 52 304 40

Scoop System: 100


Step 7 – Detailed Design

Physics Equations: Velocity, Acceleration, Linear Force, Frictional Force, Coefficient of Friction (will vary

with surface) Angular Velocity, Acceleration, Power Maximum Torque of Vex Robotics Motors Stall Torque of Motors (6.5 inch-pounds) Arm Torque and Gear Ratio Claw Torque and Gear Ratio Compound Gearing (More Torque) Drive Train Torque and Gear Ratio 4-link system dimensions and limits

Compound Gear Assembly for Arm:Compound gearing helps to increase Torque so that the arm can lift more. We have motors attached to both sides of the arm support to help prevent stall torque (max weight the motors can lift). The gear attached to the axle with the motors has 12 teeth and is meshed with a 60 tooth gear giving a gear ration of 1:5

The axle that has the 60tooth gear also has a 12 tooth gear attached to it. This 12 tooth gear is attached to an 84 tooth gear giving a gear ration of 1:7The total gear ratio for the arm is the 1:5 gear ratio multiplied by the 1:7 gear ratio which is 1x1:5x7 = 1:35 final gear ratio for the arm of the robot.

Drive Train Base:There are several options for drive train: Middle power steering, Front wheel drive, rear wheel drive, 6 wheel driver, track drive, crab drive, four wheel drive systems.

This robot uses four independent motors for each wheel. We tried to gear up the system by putting a 24 tooth gear on the motor and a 12 tooth gear on the wheels which made the robot faster but it also made it hard to slow down without tipping the robot over. In addition, it was hard to drive the robot in a straight line. After that we switched back to a straight motor to axle to wheel design.

We also switched from a base that had the wheels inside the second rail to wheels outside the rail for easy change of wheels. The design with the wheels inside was good for defense but if we needed to change a damaged wheel it would take longer.


Vex Motor Performance: Stall Torque for the Vex Motors is 6.5 inch-pounds

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%VEX Motor Motor Performance

Speed (% of Free) Current Draw (% of Stall)Mechanical Power (% of Max) Efficiency (%)

% of Stall Torque% o

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peed

, Sta

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ax P

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CAUTION: Torque displayed on x-axis

This chart is a guide to the Vex Robotics motor performance.

Independent Wheel Torque:4-link design system:This system uses the geometry of a parallelogram to make the arm go up and down but at the same time be able to keep the base perpendicular and the Intake and basket perpendicular with the level surface. In general to get mechanical advantage it works like having 2 see-saws connected together via a bracket. One controls the other via the bracket. The leverage principle at work, like in the cartoons when they take a log to push a big rock off a cliff!

Arm Mounting Base

Programming for EasyC:

4-link connection

Intake


Motor mapping (using on-line software in EasyC)

Robot Base:Front Robot

Left Side Right Side

Back of Robot

Robot Arm:Facing the back of the robot

Robot Claw:Front of Robot

Robot Intake:

Top of Intake

Back of Robot

Step 8 – Design Review

2 3

Port

1

Port

10

4 5

76


Some questions that came up during a design review:1. How can we make it more robust?

Add metal plates for weight in the rear and front of the robot

2. How can we make it smaller?We can change the lengths of the metal for the chassis

3. How can we make it simpler?Using of the intake idea and getting rid of the Pinchy claw system, it’s easier to maintain and build.

4. How can we make it more efficient?We can attach metal mounts to the back of the intake baskets to straight during goal scoring.

5. How can we make this cheaper?We can use some of the parts from last year (axles, collars, spacers, etc)

6. How can we make this easier to construct?Always use the KISS motto (Keep It Simple Silly!)

7. What other functionality would be easy to add?An additional set of gears for the top part of the compound gearing for the arm. This will help prevent the arm from slipping.

8. Why was it done this way?The path of least resistance. The less resistance the easier things flow, like water.

9. Why did you rule out other alternatives?Simple is better. Too many moving parts have too much chance going wrong. Simple is easier to repair and easy to duplicate.

10. Does it fulfill our requirements and specs?Everything is within the 18 inch box requirement.

11. How can we make it faster?Tried gearing up the motors and wheels. Had issues stopping without tipping over and also had issues with it moving straight during autonomous mode and driving.

Step 9 – Manufacturing & Implementation


The steps used to build teams 4540B robots were to do an “Assembly Line” approach; after all we are from the “Motor City”!

After the initial prototype was built we then assembled all the robots (4 totals) from the initial design.

This approach was elected because of the short time span from when we received our part to our 1st competition (3 weeks).

Stages to the building of the robot were in 3 parts:1. Chassis2. Arm3. Intake and basket

After the assembly was complete we programmed the robots to do very basic movements to test motion, arm geometry, Intake basket effectiveness, etc. Afterwards adjustments were made to maximize the functionality of the robot.

Step 10 – Testing & Analysis

During the testing phase we ran practice sessions with the playing field setup and engage in mock competitions. These competitions let us know how effective the design was. We could then make adjustments to improve reliability. Autonomous modes could also be run to see how good they worked as well.

One other thing that helped us make small improvements was actually tournament play. We saw some great designs at local competitions and borrowed the ideas to be put to work for us.

We had to have it! We worked on it right their at the event site and had it working after the lunch break. When we went to other events it gave us a quick advantage over teams that had not see this design modification yet.

Testing is an ongoing process that never ends.

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