Laboratory 4:Hardware

Analysis & SynthesisGeneral Engineering

Polytechnic University

OVERVIEW

Objectives Review Reverse Engineering Forces Gears Gear Trains Materials for Lab

Procedure Written Assignment Recitation Topics Closing

OBJECTIVES

Review the concept of sketchingUnderstand the concept of “reverse

engineering”Learn about the importance of torque & gears Use your new knowledge to find out how a

device works

REVIEW

Orthographic vs. Isometric ViewsSketching Rules

REVERSE ENGINEERING

Begins with the intact product– Works through the design process in the

opposite direction

Used to understand: – How products are made by other companies– The quality of the product

FORCESForce = m * a

Torque - French for “twist” - A twisting force = F * l

l1 l2

F1 F2

m = mass (lbs. or kg.)a = acceleration (ft/s2 or m/s2)F = Force (lbs. or Newtons)l = Distance from force to

point of rotation (ft. or m) = Torque (ft-lbs. or newton

meters)

If F1=F2, but l1<l2, the right side of the beam will tip down, due to unbalanced torque.

Equilibrium: 1= 2 F1*l1 = F2* l2

TORQUE OUTPUT OF GEARS

Small force (F1) used to lift large weight (F2)

Penalty for increased torque– small gear turns

through larger angle than large gear

F1

F2

R1 R2

– indicated in ratio of revolutions/second (gear speed) in equation: F1 * R1 = F2 * R2 (1 = 2)

GEARSUsed to increase/decrease torque or speedTorque and speed inversely proportionalVelocity ratio equals inverse of gear ratio

Output = the destination of the rotation

(e.g. a wheel)Input = the source of the rotation

(e.g. a motor)Velocity Ratio =Input

Output

Gear Ratio =OutputInput

TYPES OF GEARS

SPUR GEAR: gear wheel having radial teeth parallel to axle

CROWN GEAR: gear wheel with teeth set in rim perpendicular to its plane

crown gear

TYPES OF GEARS

IDLER GEAR: gear between two other gears to transmit motion from one to other– Changes direction of rotation – No effect on ratios– ODD number of gears

First & last gear rotate in same direction

– EVEN number of gearsFirst & last gear rotate in different direction

idler gear

SIMPLE GEAR TRAIN

Output

Input

Velocity Ratio

1” 2” 4”

n1

n2n3

2

1

4

2

4

1 *

n

n

n

n

n

n *

1

2

2

3

1

3

Gears with the same size teeth, ratio equal to ratio of number of teeth (n) on each gear.

COMPOUND GEAR TRAIN

Output

InputVelocity Ratio

n

n*

n

n

n

n1

2

3

4

5

6* n

n 7

8*

n1

n2 n5

n6

n3n4 n7

n8

Angular velocities of all gears are equal to that of the shaft on which they are mounted

MATERIALS FOR LAB

WAO II Robot– Model MV-961

– OWI Incorporated

– 2 Portions• Mechanical /

Electrical

• Computer

Toolbox with 17 tools

PROCEDUREExamining the Robot

– Inspect the intact robot

– Record the appearance of the robot

– Include sketches of the robot, complete with the outside dimensions

– Hypothesize how the robot works (Try not to look at the bottom of the WAO II)

Examining

Disassembling

Understanding

Reassembling

PROCEDUREDisassembling the Robot

– After you instructor signs your hypothesis & sketches, obtain a toolbox, complete with tools

– Take apart the robot. Do NOT break it

– Record what you see as you take the robot apart

– Sketch the inside of the robot including the gear train. Be sure to label

Examining

Disassembling

Understanding

Reassembling

PROCEDUREUnderstanding the Robot

– Describe the different components that make up the whole device

– Record the functions of the individual major parts

– Learn how the Power Gear Linkages allow:• Rotation on the axis located in the center of the

robot

• Turning (rotation outside the axis)

• Translation (movement in a straight line)

– Determine the Gear Ratio for the train of gears that link the motor to the wheels

Examining

Disassembling

Understanding

Reassembling

PROCEDUREReassembling the Robot

– Reassemble the device to working order

– Refer to the WAO II manual for assistance (disregard the sensor portion of the manual)

– Return the assembled WAO II to the box and give it to you instructor

– Record any further observations, including improvements to the robot and assembly instructions

Examining

Disassembling

Understanding

Reassembling

WRITTEN ASSIGNMENT

Use the form report on Page 55 to complete the lab report (Be sure to type out your answers on a different piece of paper)

Include original sketches with the instructor’s initials

Remember to create a title page

RECITATION TOPICS

Explain how the device works Discuss components of the WAO II and their

functions How do the parts fit together? Discuss the overall construction of the device Discuss the assembly instructions for the WAO II.

Are they clear? If so, explain what is clear. If not, what changes would you make to the assembly instructions?

Discuss you findings for the gear ratio.

CLOSING

Be sure to label your sketchesAvoid breaking partsKeep track of the pieces