Laboratory 4:
Hardware
Analysis & Synthesis
General Engineering
Polytechnic University
OVERVIEW
 Objectives
 Procedure
 Review
 Written Assignment
 Reverse Engineering
 Recitation Topics
 Forces
 Closing
 Gears
 Gear Trains
 Materials for Lab
OBJECTIVES
 Review the concept of sketching
 Understand 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 Views
 Sketching 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
FORCES
Force = m * a
Torque - French for “twist”
- A twisting force
t=F*l
If F1=F2, but l1<l2, the
right side of the beam
will tip down, due to
unbalanced torque.
l1
F1
Equilibrium:
t1= t2  F1*l1 = F2* l2
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)
t = Torque (ft-lbs. or newton
meters)
l2
F2
TORQUE OUTPUT OF GEARS
 Small force (F1) used to
lift large weight (F2) F
1
 Penalty for increased
R1
R2
torque
– small gear turns
through larger angle
than large gear
– indicated in ratio of
revolutions/second (gear speed) in
equation: F1 * R1 = F2 * R2 (t1 = t2)
F2
GEARS
 Used to increase/decrease torque or speed
 Torque and speed inversely proportional
 Velocity ratio equals inverse of gear ratio
Output
Gear Ratio = Input
Output = the destination of
the rotation
(e.g. a wheel)
Input = the source of the
rotation
(e.g. a motor)
Input
Velocity Ratio = Output
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 idler gear
rotate in same direction
– EVEN number of gears
First & last gear rotate in different direction
SIMPLE GEAR TRAIN
n3
n2
n1
1”
2”
Gears with the same
size teeth, ratio equal
to ratio of number of
teeth (n) on each 1
gear.
 *
2
4”
 Input 


Velocity Ratio  Output 
2
1
n1 n2 n1
 

*
4
4
n2 n3 n3
COMPOUND GEAR TRAIN
n1
n3
n2
n4
Angular velocities of all
gears are equal to that of
the shaft on which they are
mounted
n6
n5
n7
n8
 Input 

Velocity Ratio 
 Output 
n1 n3 n5 n7

*
*
*
n2 n4 n6 n8
MATERIALS FOR LAB
 WAO II Robot
– Model MV-961
– OWI Incorporated
– 2 Portions
• Mechanical /
Electrical
• Computer
 Toolbox with 17
tools
PROCEDURE
Examining
Disassembling
Understanding
Reassembling
 Examining 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)
PROCEDURE
Examining
Disassembling
Understanding
Reassembling
 Disassembling 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
PROCEDURE
Examining
Disassembling
Understanding
Reassembling
 Understanding 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
PROCEDURE
Examining
Disassembling
Understanding
Reassembling
 Reassembling 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
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 sketches
 Avoid breaking parts
 Keep track of the pieces