University of Notre Dame

Department of Aerospace and Mechanical Engineering

Matt Bertke, Paul DeMott, Patrick Hertzke, Will Sirokman

7 December 2004

AME 470: Senior DesignASME Bulk Material Transporter

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Executive Summary

1. ASME Student Design Competition: Bulk Material Transporter

2. Critical Constraints and Requirements

3. Early Concept Development

4. Critical Design Issues

5. Strengths and Weaknesses

6. Failure Modes

7. Future Development

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ASME Problem DescriptionObjective

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• Design a remote-controlled vehicle to navigate the stair course.

• Transport a granular payload from the starting area and deliver it to the receiving box.

• Transport as much grain as possible in a 10-minute time period.

Starting Area Receiving Box

12 inches

ASME Problem DescriptionCritical Requirements and Constraints

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• Vehicle dimensions must not exceed 25 cm x 25 cm x 30 cm. (ASME)

• Energy sources limited to eight 1.5 V batteries or ten 1.2 V batteries, in addition to two 9 V batteries. (ASME)

• Remotely controlled via radio or umbilical. (ASME)

• $500 budget. (ND)

• 14 – week concept development and manufacturing period. (ND)

Early Concept DevelopmentPrimary Design Objectives

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• High Payload

• Efficient Operation

• “Intelligent” Electronics

Primary Design Objectives:

5 lbs of rice per trip

At least 2 trips in 10 minutes

Allows variable motor-speed control using potentiometers.

Ability to automate stair navigation tasks using position sensor(s).

Provides a flexible software platform that can be modified for a number of different tasks.

Mini-Max Microcontroller

Early Concept DevelopmentPreliminary Concepts

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• Sensitive to changes in center of mass.

• High torque required for swing arm.

Swing Arm Concept

Hinged Tread Concept

• Simple design and operation.

• High payload capacity.

• Complex mechanical design.

• Low grain capacity.

• Fluid motion up stairs.

• High traction.

STRENGTHS

STRENGTHS

WEAKNESSES

WEAKNESSES

Early Concept DevelopmentPrototype Testing and Final Design

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•A LEGO prototype of the single swing arm design to test functionality.

•Design flaw discovered: Both lifting actions of swing arm require different locations of center of mass.

•Solution: New design with two sets of swing arms.

•Final Design utilizes short front swing arms and long rear swing arms. Swing arms are geared together 180° out of phase.

Revised LEGO Prototype/Final Climbing Process

1) Align Vehicle 2) Front Arms Down

3) Rear Arms Down 4) Drive forward/Repeat

Final Concept and PrototypeVideos of Prototype Operation

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Critical Design IssuesSwing Arm Geometry

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Applies a moment about the rear wheels – mechanical advantage maximized if front arm axle is farther forward.

Axle placement limited by reverse rotation of the front swing arm.

Shorter arm requires less motor torque.

Front Swing Arm:Design Considerations

Design Choice Axle located at center of vehicle wheelbase.

3.3” arm length.

Rear Swing Arm:Design Considerations

Applies a moment about the front wheels – mechanical advantage maximized if front arm axle is farther back.

Shorter arm requires less motor torque, but arm must extend at least 4” below bottom of treads due to stair height.

Design Choice Axle located 1.25” forward of rear wheel axle.

5.25” arm length.

Critical Design IssuesSwing Arm Torque

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866.330sin60cos25.430cos

)60cos()866(.60sin)5.6(

mgmg

FFTMO

Centerof Mass

Chassis

Rear SwingArm

Pivot Point “O” Static and dynamic force analyses conducted to predict necessary arm torque.

Longer rear swing arm requires more torque than front swing arm.

Based on a 10 lb combined vehicle and payload weight, static lifting torque was estimated at > 2.4 Nm.

A 4.0 Nm gear motor was incorporated into final prototype due to availability and to increase payload capacity.

Critical Design IssuesCenter of Mass

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Center of Mass:

Acceptable domain for the vehicle center of mass is dictated by swing arm geometry.

Must lie between the two swing arm axles (3” apart).

Cannot lie behind the rear tread wheel when the vehicle is inclined.

RESULT: Final prototype is balanced such that it can operate successfully with a full payload or completely empty.

Critical Design IssuesOther Important Issues

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Rice Container Design:•Unique geometry of container is defined by ASME constraint.

Rice Door Mechanism:•A counter-weighted lever mechanism was implemented to gain mechanical advantage due to a solenoid that was weaker than expected.

Rice container in white fits just within the ASME constraint size (gray box)

Vehicle successfully delivering a full payload of rice (approximately 7lbs)

20 °

Solenoid

Hinged Door Support

Counter-weighted Lever

Front Drive Motors

•From Trade Study, Required Torque = .15 Nm

•From Testing Prototype, Max Speed = 50 - 60 RPM

Chosen MotorHsiang Neng – 38GM - 60

Part # 253500CR

Drive motors

Rice Container Design:•Unique geometry of container is defined by ASME constraint.

Rice Door Mechanism:•A counter-weighted lever mechanism was implemented to gain mechanical advantage due to a solenoid that was weaker than expected.

Critical Design IssuesElectronics

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PHILOSOPHY

• Use a microprocessor and automation to make operation simple and precise.

APPLICATION

• Microprocessor adds precision

• Pulse width modulation (PWM) and

H-bridges allow variable tread speed.

• Angular encoder allows precise,

computer controlled arm movement.

• Automation

• Automated algorithm is initiated by user.

• User can interrupt computer or override with manual control.

Mini-Max Board (PIC 16F877a Processor)

H-Bridge

Critical Design IssuesElectronics

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PROGRAMMING OF MINI-MAX PROCESSOR

•DESIGNED FOR FUNCTIONALITY

• Functions built and tested individually.

• Functions can be easily added/removed.

•CODE STRUCTURE

•Main loop comprises seven function calls

•All input evaluated before change in output.

•High speed evaluation ensures that input is not missed. (Rechecks inputs every cycle (at about 2000 Hz)

•Code allows simultaneous inputs and conflicting commands.

STRUCTURE OF MAIN()

[Initialization];

While (true){ [Check for algorithm button press]; [Check for change in encoder signal]; [Check current potentiometer input]; [Check for manual arm control];

[Drive the motors]; [Drive the swing arms]; }

Solenoid

Mini-Max Microprocessor

5V

9V Battery

12V Battery

9V Battery

Manual swing-arm fwd

Manual swing-arm rev

Ascend Algorithm

Descend AlgorithmMotor Brake

Potentiometer 1

Potentiometer 2

Reset

4.7k

4.7k 4.7k

4.7k 4.7k

10k

4.7k

10k

2A Fuse

2A Fuse

2A Fuse

H-Bridge 1

H-Bridge 2

H-Bridge 3

Rotary Encoder

Regulator

Drive Motor L

Drive Motor

R

Swing Arm

CIRCUIT LAYOUT

•Power Input. Two 9V and one 12V battery.

•Umbilical Inputs. Pull down (4.7k resistors).

•Rotary Encoder Input.

•Outputs. Signal to H-Bridges.

•Motors. Driven by H-Bridges.

•Solenoid. Separate circuit.

Final Concept and PrototypeStrengths of Concept and Prototype

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OVERALL• Robust design

• High capacity – 8 lb per trip

• Climbs quickly and efficiently - 3 minute round trip

• Automated and programmable

TREADS• Tread teeth provide lever effect

• Independent, variable speed control

SWING ARM MECHANISM• Accurate, computer controlled angular rotation

• Applies strong, consistent force

• Aligns vehicle as it lifts

DUMPING MECHANISM• Reliable latched mechanism

• Efficient: gravity assisted fall minimizes energy usage

Final Concept and PrototypeWeaknesses of Concept and Prototype

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WEAKNESSES OF FINAL CONCEPT

• Complexity of design – 288 parts

• Large number of manufactured parts – 20 different parts

• Heavy – 7 lb

• High Cost – over $500

WEAKNESSES OF PROTOTYPE

• Unknown electrical problems: interference, shorts, over heating??

- Result: Automation disabled to simplify electronics

• No variable speed reverse

• Inefficient and error prone turning procedure

• Poor traction of flat surface of stairs

Final Concept and PrototypeLikely Failure Modes

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RICE DUMP FAILURE

• Dumps without button press•Human bumps latch (unresolved)

• Fails to dump on button press

LOSS OF CONTROL

•Hardware failure•Electronic interference/other issue (unresolved)

•Code failure•Maximum H-Bridge frequency exceeded

(may be unresolved – reverse PWM disabled)

Final Concept and PrototypeFuture Development

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FUTURE ELECTRONICS DEVELOPMENT• The use of the microprocessor provides potential for further refinement

• Shield electronics from heat, interference, impact

• Incorporate reverse PWM

• Incorporate automation climbing algorithm

• Refine turning procedure

FUTURE MECHANICAL MODIFICATIONS• Replace shafts with precision ground shafting

• Re-fabricate and realign tread assemblies

• Improve swing arm clamping mechanism

• Add safety latch to rice bin

• Modify rice bin to ensure complete release of rice

• Seal chassis and electronics from rice

Questions?

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