laboratory 4: reverse engineering. overview objectives concepts materials procedure report /...
TRANSCRIPT
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Laboratory 4:Laboratory 4:Reverse EngineeringReverse Engineering
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OverviewOverview
• Objectives• Concepts• Materials• Procedure• Report / Recitation• Closing
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ObjectiveObjective
• Take apart a robot– Measure its gear and velocity ratios– Sketch all gear trains
• Introduce the concept of reverse engineering, gears and torque
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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MaterialsMaterials
• Assembled robot that a different team built in the previous lab
• NXT kit
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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
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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
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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
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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)
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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