Laboratory 4 Reverse Engineering Overview Objectives Concepts Materials

Laboratory 4: Reverse Engineering

Overview • • • Objectives Concepts Materials Procedure Report / Recitation Closing

Objective • 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 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 Torque equilibrium: Torque - French for “twist” - Created by a twisting force If F 1=F 2, but L 1<L 2, the right side of the beam will tip down, due to unbalanced torque. L 1 F = Force (lbs. or Newtons) L = Distance from force to point of rotation (ft. or m) = Torque (ft-lbs. or Newton meters) L 2 F 2

Gears • Small force (F 1) used to lift large weight (F 2) F 1 • Penalty for increased R 1 torque - small gear rotates more than large gear • Indicated in ratio of revolutions/second (gear speed) in equilibrium equation: R 2 F 2

Gears • • 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)

Gears • Crown Gear: gear wheel with teeth set in rim perpendicular to its plane crown gear • Worm Gear: gear with one tooth that spirals down the length of a shaft • Spur Gear: gear wheel having radial teeth parallel to axle Worm Gear

Gears • 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

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 idler – EVEN number of gears First & last gear rotate in different direction gear

Gears n 3 n 2 n 1 1” 2” 4” For gears with the same size teeth, the ratio is equal to the number of teeth (n) on (or radius of) each gear

Compound Gear Train n 1 n 3 n 2 n 4 n 6 n 5 n 7 n 8 Angular velocities of all gears are equal to that of the shaft on which they are mounted

Materials • Assembled robot that a different team built in the previous lab • NXT kit

Procedure üExamining üDisassembling üUnderstanding • 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

Procedure üExamining üDisassembling üUnderstanding • 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

Procedure üExamining üDisassembling üUnderstanding • 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!

Assignment: 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)

Closing • 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