Mechanical Engineering Drawing MECH 211M Lecture 12 Dr

Mechanical Engineering Drawing MECH 211/M • Lecture #12 • Dr. John Cheung

Notice • Exam Date Change Sunday Dec 7 th at 9: 00 to 12: 00 H 607 AA-LA H 609 LB-SA H 611 SB-ZZ • Review Session Tuesday Dec 2 nd at 8: 30 to 11: 00 Location: FG B 060 • Assignments Outside my office 2

Gastraphetes • First catapult design • Braced up against the belly • Both hands used to draw the string • More powerful than a regular bow 3

Oxybeles • Fix mount replaced the belly mount • Size increased • Power came from the bending of wood 4

Ballista • Fundamental shift in power source – twisting of ropes • Still used two wooden arms • Still resembled a bow 5

Mangonel • Used a single arm • Torsion power from ropes • Payload was put in the bucket • Payload was not arrowlike • When released the arm would hit the crossbar and payload would be released 6

Onager • Variation of a Mangonal • Used rope & sling instead of a bucket • More efficient 7

Trebuchet • Gravity powered • Could be very large • Counter weight is much more massive then the payload 8

Checklist for a Good Design • Is the drawing easy to read? • Are the part outlines distinct from dimension lines? • Is the lettering neat and clear? • Is all of the information on the drawing? • Will the drawing make a good print? • Have all the rules of standard drafting practices been followed? 9

Checklist for a Good Design • Is the nomenclature correct? Will everyone understand it the same way? • Is the drawing title truly descriptive? • Are all the necessary views given? • Are all the dimensions shown? • Is there double dimensioning? • Are all the notes properly located? • Could any of the notes be misunderstood? 10

Checklist for a Good Design Do the parts agree with the part list? Are the standard parts specified correctly? Is the scale designated? Are the finishes specified in the drawing? Is a heat treatment recommended? Have standard manufacturing processes been followed? • Can the part be produced simpler and more economically? • • • 11

Checklist for a Good Design • Are the materials specified? • Are the standard parts used as much as possible? • Are the suppliers for the standard parts indicated? • The design is yours. Are you ready to approve it? 12

Design a Catapult • You are an engineer (that is good to know and even better to start imagining being one) • Your kid brother or sister is asking you to make a catapult for them for playing during the winter season • What are things that you should know to design and manufacture this catapult 13

Needs and Functionality • What you are going to throw? • How fast you want to throw a particular object? • The range of the catapult? • What will be the working mechanism? • How are you going to design that? • How are you going to produce it? 14

Preliminary Design Constraints • The part you are going to throw with your design is “assumed to be the eraser that you use in drawing class” • It has to be thrown a minimum distance of 10 meters • Since you are designing this for your kid brother or sister, you cannot use unsafe mechanisms like Nothing that give out lot of energy No explosive materials etc No petroleum based fuels No heat to power the device 15

Design Requirements • Use a minimum number of parts in the assembly (<15) • Use power sources like Spring Air cylinder Rubber band • Use as many standard parts in your design as possible 16

Design Review Criteria 17

Best Designs! • First place – 10% • Second place – 7% • Third place - 5% 18