Laboratory 4:Laboratory 4:Reverse EngineeringReverse Engineering
OverviewOverview
• Objectives• Concepts• Materials• Procedure• Report / Recitation• Closing
ObjectiveObjective
• Take apart a robot– Measure its gear and velocity ratios– Sketch all gear trains
• Introduce the concept of reverse engineering, gears and torque
Concept: Reverse EngineeringConcept: Reverse Engineering
• Learning how a device works – Beginning with the intact product– Taking it apart – Noting key components
• Uses:– Understanding how a product is made– Testing quality of product
Concept: Forces and TorqueConcept: Forces and Torque
Torque - French for “twist”
- Created by a twisting
force
L1 L2
F1 F2
If F1=F2, but L1<L2, the right side of the beam will tip down, due to unbalanced torque.
Torque equilibrium:
221121 LFLF LFTorque
F=Force (lbs. or Newtons)L=Distance from force to
point of rotation (ft. or m)=Torque (ft-lbs. or Newton
meters)
GearsGears
• Small force (F1) used to lift large weight (F2)
• Penalty for increased torque- small gear rotates
more than large gear
F1
F2
R1 R2
• Indicated in ratio of revolutions/second (gear speed) in equilibrium equation: 2211 RvRv
GearsGears
• Used to increase/decrease torque or speed• Torque and speed are inversely
proportional• Velocity ratio equals inverse of gear ratio• Values for Output and Input are the
diameters of the respective gears
Output = destination of the rotation
(e.g. a wheel)
Input = source of the rotation(e.g. a motor)
Output
InputRatioVelocity
Input
OutputRatioGear
GearsGears
• Crown Gear: gear wheel with teeth set in rim perpendicular to its plane
• Worm Gear: gear with one tooth that spirals down the length of a shaft
• Spur Gear: gear wheel having radial teeth parallel to axle
crown gearWorm Gear
GearsGears
• Rack Gear– A flat rectangular gear that has teeth running
perpendicular to the axis of the gear – Rack gear changes direction of motion
perpendicularly– Also changes motion from a rotation to a linear
translation
Rack Gear
GearsGears
• 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
GearsGears
1” 2” 4”
n1
n2n3
For gears with the same size teeth, the ratio is equal to the number of teeth (n) on (or radius of) each gear
4
1
4
2
2
1
Output
InputRatioVelocity
3
1
3
2
2
1 n
n
n
n
n
n
Compound Gear TrainCompound Gear Train
n1n2 n5
n6
n3 n4 n7n8
Angular velocities of all gears are equal to that of the shaft on which they are mounted
8
7
6
5
4
3
2
1
Output
InputRatioVelocity
n
n
n
n
n
n
n
n
MaterialsMaterials
• Assembled robot that a different team built in the previous lab
• NXT kit
ProcedureProcedure
• Examining the Robot– Inspect intact robot– Create sketches of robot, complete
with outside dimensions• Front• Top• Most detailed side • Gear train
– Record appearance of robot• Use digital camera (request photo from
TA)
– Hypothesize how robot works
Examining
Disassembling
Understanding
ProcedureProcedure
• Disassembling the Robot– Take apart robot
• Do NOT break it
– Record what you see as robot is dismantled
– Sketch robot and gear train– Label important parts
Examining
Disassembling
Understanding
ProcedureProcedure
• Understanding the Robot– Describe different components– Record functions major parts – Establish how power is
transferred from motor to ground
– Determine Gear Ratio for gear train linking motor to ground• Recall that a wheel is part of a
gear train!
Examining
Disassembling
Understanding
Assignment: ReportAssignment: Report
• Individual report• Title page• Discussion topics in the manual• Include original data with instructor’s
initials– Scan in data and lab notes
(ask TA for assistance)
ClosingClosing
• Disassemble robots and return sorted parts to kits
• Have all original data signed by TA
• Submit all work electronically
• Return all unused materials to TA
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