INTRO TO MECHANICS

• BILL WASHABAUGH

Review

• What they learned.

• Class 1 assignments

• Review electronics class

Preview of Mechanics

• Why make art move?Because it’s new, it’s fun, it’s challenging, it’s engagingThe tools/methods are widely available, the tools are getting better/easier, the resources are getting better.

• But, IT’S NOT EASY

• Reliability.

• This takes, diligence, creativity, trial and error, and lots of time.

goals of this class

• AC/DC electricity• Understand basic elements of sensing,

processing, control• Understand mechanical elements • how thing work together to make things move• basic physical understanding of main

mechanical elements• structure for approach to design• combining electronics and mechanical stuff• resources

Assignment

• Create a simplified mechanical sculpture, wire frame. Moving. Take short video, upload to Youtube and post the link on the wiki.

Basic of a machine• Processing and control through mechanical elements• AC/DC – DC for sensing and control, possible AC for motors (or

DC)• Sensing can be DC digital or analog• DC digital sensing: typically either 0V or 5V, nothing else.• AC digital sensing: any number between 0V and 5V • Common DC voltages: 12V, 24V, 48V• Common AC voltages: 110, 220 AC single phase.• Sensing – eyes, ears, nose - switches, sensors, • Processing – brains – logic gates, valve gates, processors, etc.• Control – hands, feet – motors, solenoids, pistons, etc

It takes energy to make movement

• Types of energy:• Electricity• Wind• Pressure• Thermal – radiative, conductive, convective• Solar• Nuclear• Human input• Kinetic - moving• Potential – usually height, or a compressed spring

Converting energy to do work

• Thermal energy:• Motor – internal combustion, radial, Stirling (heat

exchange = efficiency)• (piston engines = gas, diesel, hydraulic, air..)• Fluid energy: • water, hydraulic, wind, turbine, etc• Electrical:• Electrical motor – AC, DC

Energy to work (con’t)• Solenoids• Kinetic:• Spring: compression, tension, torsion, spring steel (custom)• Potential:• Compressed fluid, capacitors, batteries.• Other Thermal:• Shinking, expanding materials based on temperature change• Other electrical:• Ferrofluid, changes viscosity with electrical charge• Also – wire changes length with electrical current• Also, think of nature• More complex systems for converting energy to work

Review of physics principals that are important

• Force - N, Lbf• Distance – in, m• Rotational Distance – degrees, radians• Torque - in-lb, oz-in, N-m • Time – s, min• Basic Geometry• Work (linear) = F*d = joules• Work (rotational) = T * θ, where θ is in radians• Power = W/t = joules/sec = watts (1 W = 1 j/s). • Where else do we know power from? Electrical!• P = I V

Mechanical Elements Overview

• Motors• Springs• Gas Springs• Gears• Pulleys• Wedge (inclined plane)• Rotary to slider• Linkages• Pneumatics/ Hydraulics• Bearings, bushings, screws, nuts, etc.

Motors

• electrical, hydraulic, or combustion, the same principals apply:

• RPM• Torque• RPM is used to determine the rate of shaft

rotation• Torque and RPM determines Power output (HP,

watts, etc)• Not going to cover IC, Turbine, Thermal, or

Hydraulic

Electrical motors

• AC, Brushed DC, Brushless DC, Stepper DC

• AC, single phase. Simple, cheap, no position control, low starting torque. Works with a triac for speed control (light dimmer, but use a snubber to make sure it turns off, doesn’t false trigger).

• AC, 3 phase. Bigger motors, more common in industrial use (220v, 380v).

Brushed DC Motor

• Easiest DC motor to control.• Cheap, and easy to find• Usually spin ~ 1750 rpm• Very simple, +12vdc one way, or reverse.

That’s it!• No position control, no speed control• Brushes wear• Stator, Rotor, commutator

Brushless DC Motor

• Must have a motor controller board

• Speed control through the controller board

• No position control

• No brushes to wear, so long life.

DC Stepper

• Has position control – you know where the shaft is at all times

• Requires electronics for control

• Relatively low cost

• Can be found in old printers, etc.

• Brushless DC, Servo, or Stepper. Requires external commutation, usually through electronics.

Springs• What do springs do?• Usually made of spring steel, Higher deflection before taking a set.

High resistance to fatigue. Also, rubber, etc.• Compression, Tension, Torsional, custom, gas• F = kx (where K is a spring constant)• Note maximum, minimum extents• Compression spring usually need position constraint so they don’t

buckle.• Tension springs are easy• Torsional springs, LF or RH winding• Custom spring, spring steel, etc.• Gas shocks. Already have position constraint.

Gears• Examples• What do gears do: change torque and change speed, change

direction• Moderate prices.• Can make your own with semi-accurate machining (for large gears)• Bevel Gear• Must have same Pitch and Pressure Angle• R1 to R2 ratio gives, speed/torque ratio• Miter Gears• 90 angle, or otherwise• Worm Gears• Usually high ratio. Generally do not back-screw• Rack & Pinion• Planetary

Pulleys

• What do pulleys do? • Change torque, direction, speed. Similar to

gears, but across great distances.• Block and tackle, cheap• Timing belt pulley, more expensive.• Block and Tackle – sailing style – pulley can be

used to increase torque.• Belt Pulleys. Transmit Force – timing belt style

or friction style.• Belts often require a tensioner.

Wedge/ Inclined plane

• Examples: wedge, hill, cam roller, screw.• What does it do: • Change force direction.• Change speed.• Includes screws and nuts• ACME screws• Ball screws• Linear Actuator

Rotary to slider

• Examples?

• What does it do: change rotary motion to linear motion

• Linkages

• 4 bar linkages (think Theo Jansen)

Pneumatics/ Hydraulics

• Examples:• What does it do: transfer power over distance. • Very similar to electricity.• Very easy to multiply force/torque/speed. • Easy sensing and control.• Mechanical switching through valves. • Very high forces possible with Hydraulics.• Expensive.• Initial learning curve can be difficult.• Explain the principles of Pascal’s Law• Pneumatics:Air – up to about 100 psi• Hydraulics: Oil – up to about 3500 psi

Bearing, Screws, etc.

• Bushings (radial, linear)

• Bearings (radial, roller, angle, thrust, mounted)

• Screws, nuts.

CAD design

• Why?

• rigor

• Process

• Planning

• Collaborating

• Proposals

Resources

• You garage, shop, junk drawer• HomeDepot, Lowes, etc• Radioshack (for electronics parts)• Mcmaster.com (mechanical parts)• Digikey.com (electrical parts)• Mouser.com (electrical parts)• Allelectronics.com (electrical and mechanical)• Sparkfun (sensing and processing)• Adafruit (sensing and processing)