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

2. Notice Exam Date Change Review Session Assignments
Sunday Dec 7th at 9:00 to 12:00
H607 AA-LA
H609 LB-SA
H611 SB-ZZ
Review Session
Tuesday Dec 2nd at 8:30 to 11:00
Location: FG B060
Assignments
Outside my office

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

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

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

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

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

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

9. 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?

10. 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?

11. 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?

12. 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?

13. 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 the things that you should know to design and manufacture this catapult

14. 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?

15. 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

16. 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

17. Design Review Criteria

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