Lab # 3: The Programmable Robot General Engineering Polytechnic University

Overview Force Torque Gears Torque Output Simple Gear Train Alternate Ratio Compound Gear Train Gear Ratio and Velocity Ratio Accuracy and Precision Problem Objectives Procedure Testing Distance Test Angle Test Time Test Questions Proficiency Test #2: Excel Closing

Force = m*a m = mass (lbs. or kg.) a = acceleration (ft/s 2 or m/s 2 )

Torque  = F * l French for “twist” F = Force [lbs. or Newtons] l = Distance from force to point of rotation [ft. or m]  = Torque [ft-lbs or Newton meters] Equilibrium:  1 =  2  F 1 *l 1 = F 2 * l 2 l1l1 l2l2 F1F1 F2F2

Gears Used to increase/decrease torque or speed Penalty for increased torque –small gear turns through larger angle than large gear –indicated in ratio of revolutions/second (gear speed) in equation below (  1 =  2 ) w 1 * R 1 = w 2 * R 2 Torque and speed inversely proportional Velocity ratio equals inverse of gear ratio

Spur Gear SPUR GEAR: gear wheel having radial teeth parallel to axle

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

Worm Gear WORM GEAR: short rotating screw that meshes with teeth of another gear

Pinion Gear PINION: small cogwheel, teeth of which fit into those of larger gear wheel pinion gear

Idler Gear Between two other gears to transmit motion from one to other Changes direction of rotation No effect on ratios ODD number = reverse rotation EVEN number = same rotation idler gear

Torque Output Small force (F 1 ) used to lift large weight (W 2 ) F1F1 W2W2 R1R1 R2R2

Simple Gear Train 1”2”4”

Alternate Ratio n1n1 n2n2 n3n3 Gears with the same size teeth, ratio equal to ratio of number of teeth (n) on each gear

Compound Gear Train n1n1 n2n2 n5n5 n6n6 n3n3 n4n4 n7n7 n8n8 Angular velocities of all gears are equal to that of the shaft on which they are mounted

Gear Ratio and Velocity Ratio Gear Ratio =Velocity Ratio = Simple Gear Train Compound Gear Train Gear Ratio =Velocity Ratio =

Accuracy and Precision Accurate Precise Inaccurate Precise Accurate Imprecise Inaccurate Imprecise

Accuracy and Precision Average (mean) N = # of measurements P = parameterA p = average Accuracy (error) P s = standard Precision (repeatability) 123N sp nn nn

Problem You have just been hired by an engineering firm that makes robots for sale for a little less than $ Your boss has asked you to build and test this prototype, and to make suggestions for improving the instructions before final printing.

Objectives Suggest improvements to assembly instructions Learn importance of understanding instructions and components BEFORE assembly Understand related concepts Troubleshoot Write/Test programs to evaluate performance Make necessary calculations

Procedure Take notes as you work to help you answer questions Refer to assembly instructions throughout lab Analyze components Assemble robot Understand gear linkages Determine gear ratio Perform three tests

Testing Draw expected straight line path Distance Test Angle Test Time Test Results will be used for Excel Proficiency

Distance Test Run robot for 3 units of time Standard = (Distance traveled by 3) / 3 Distance robot should run for 5 units of time = standard value * 5 Repeat 10 times: –Run robot for 5 units of time –Measure the distance STARTEND

Angle Test Use data from the distance test Draw straight lines from origin to points Measure each angle of deviation (  ) Determine accuracy and precision Determine standard STARTEND 

Time Test Choose distance for robot to travel (should be more than 2 feet) Set robot to run on straight path infinitely Measure amount of time robot takes to travel chosen distance (first trail is standard) Repeat 10 times using same distance STARTEND

Questions Discuss assembly instructions for WAO II. Were there any pieces missing? What does “M2.3 X 8” mean on a screw? Discuss power gear linkages that permit: –Rotation on axis located in center of robot –Turning/Rotation on axis outside of center –Translation/Movement in straight line Determine gear ratio/velocity ratio.

Questions (cont’) Efficient/Accurate way to count gear teeth What crown gear does that spur gear doesn’t What are two identical springs for Where friction used rather than cement Why two plastic pieces were not single mold Testing methods and results Average values and maximum deviation Determine accuracy/precision

Proficiency Test #2 Excel Use results of all three tests Follow format in manual Include: –Title page (include source of data) –Chart comparing your data to someone else’s –Legends with charts (not illustrated in manual) –Table of ONLY your data for each test (more trials may be included)

Closing If failed, discuss possible reasons for failure Include recorded observations: –All written observations –Sheets with plotted data Original data must be signed by TA Use Excel to organize report data Make sure ALL questions are answered