WELCOME!

Attendance

About me

Your turn: Name, year at ITP, background, why you are taking this class

Syllabus

Theo Jansen video: "The walls between art and engineering exist only in our minds"

Similar kinematics, easier to wrap your brain around: paper horse

Movement is beautiful. Art is beautiful. But art didn't start to move until and engineer hit the scene: Alexander Calder's Circus and mobiles

Fabrication Options

• ITP Machine Shop, http://itp.nyu.edu/physcomp/Tutorials/LaserCutting laser cutter
• AMS Laser cutter and 3D printer
• Other Resources and map

What is a machine?

Any device that helps you do work, from a hammer to a typewriter. Uses of machines:

• Transform energy - wind turbine
• Transfer energy - drive train (can opener)
• Multiply/change direction of force - pulleys
• Multiply speed - bicycle

SIX SIMPLE MACHINES:

1. Lever
2. Block and Tackle (Pulley)
3. Wheel and Axle
4. Inclined Plane and Wedge
5. Gear
6. Screw

Lever

A lever is a rigid object used with a pivot point or fulcrum to multiply the mechanical force on an object

• Three classes of levers: Each type has a fulcrum, load, and effort
  1. Fulcrum is between effort and load
     • Ex: seesaw, crowbar, shoehorn, oars, can opener
     • Double lever: pliers, scissors
  2. The load is located between the effort and the fulcrum
     • Ex: wheelbarrow, nutcracker
  3. The effort is between the load and fulcrum
     • Ex: Mandible, biceps, fishing rod

3 lever types in one

Pulleys (a.k.a. Blocks, Sheaves)

Closed system: pulleys on fixed lengths of rope or belt that's constantly tight
Used to transmit rotational motion between axes. Only mechanical advantage if INPUT is smaller than OUTPUT pulley

• Example: timing belt, Cupcake CNC

Open systems: one end is open or loose

• Example: flag hoist

1 fixed pulley does not magnify force or direction
However, 1 un-fixed pulley can: a runner
Next step: gun tackle. Use another pulley to change the direction of pull. Mechanical advantage stays the same.
Next step: higher mechanical advantage using a "luff tackle" - two sheaves at top, one movable on bottom.

Wheel and Axle

A simple wheel and axle gives you mechanical advantage: steering wheel, door knob
A wheel and axle can also be used to increase speed, at a mechanical disadvantage: bicycle
Note: We're only talking about wheel-and-axle machines that consist of a wheel or crank rigidly attached to the axle.

Inclined Plane and Wedge

Example: Movers loading boxes into truck on a dolly
Where is mechanical advantage? Small force over long distance vs. large force over short distance
A wedge is a special application of an inclined plane: 2 of them back to back
Example: axes, chisels
Mechanical advantage? Width vs. Length

Gears

Pitch diameter, diametral pitch, number of teeth, center to center distance
More on gears in a future class

Screws

A screw is really just a modification of an inclined plane (it’s an incline plane wrapped around a cylinder)
Generally used to raise things with mechanical advantage: house, car, heavy machinery

• Like any system, the mechanical advantage (MA) is the ratio of what get out to what you put in

Ex: Say a screw jack has a handle length r=2 ft. For one revolution, 2*pi*r, the screw raises a height of p (pitch). If the pitch is ¼”, and MA=(2*pi*R)/P, MA=603

• The actual MA will be lower due to friction
• Note: These type of screws are cut at a “self locking” angle.

Examples: Micrometer, Turnbuckle
Types of Power Screws:

• Acme screw
  • 30-50% loss from friction
  • Will not unwind
  • Low speeds: Wildflower Meadow Glacier, Video download
• Ball screw
  • ~90% efficient

Also used in positioning systems where mechanical advantage isn't the concern:

• Velmex
  

Complex machines are just combinations of 2 or more simple machines

Materials

Material Properties: yield strength, ductile vs. brittle, density
Material Failure: Tension, Compression, Shear, Torsion, buckling, fatigue