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INTRO TO MECHANICS

INTRO TO MECHANICS. BILL WASHABAUGH. Review. What they learned. Class 1 assignments Review electronics class. Preview of Mechanics.

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INTRO TO MECHANICS

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  1. INTRO TO MECHANICS • BILL WASHABAUGH

  2. Review • What they learned. • Class 1 assignments • Review electronics class

  3. 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.

  4. 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

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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

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

  12. 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

  13. 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).

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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

  21. Rotary to slider • Examples? • What does it do: change rotary motion to linear motion • Linkages • 4 bar linkages (think Theo Jansen)

  22. 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

  23. Bearing, Screws, etc. • Bushings (radial, linear) • Bearings (radial, roller, angle, thrust, mounted) • Screws, nuts.

  24. CAD design • Why? • rigor • Process • Planning • Collaborating • Proposals

  25. 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)

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