Electrical Systems for Robotics I

1. Manitou Springs High School Electrical Systems for Robotics I

2. Electrical Systems for Robotics • Part I • Fundamentals • Hydraulic Analogy • Alternating Current • Direct Current • Power Sources • Power Devices • Intro to Electrical Systems

3. Electrical Systems for Robotics • Part II • Electrical Systems • Components • Distribution • Wiring • Circuit Breakers • Fuses • Application to Robotics • Actuators – Motors, Solenoids • Sensors – Speed, Distance • Control System – Computer, Drive station

4. Why electricity? • It’s Magic • As magically real as anything anywhere • A convenient source of power for so many things • Allows us to do more and go farther than without • Can be harnessed, captured, engineered and utilized to provide light, transportation, logic

5. What is electricity? • Electricity is the set of physical phenomena associated with the presence and flow of electric charge. • Electricity gives a wide variety of well-known effects, such as lightning, static electricity, electromagnetic inductionand the flow of electrical current. • In addition, electricity permits the creation and reception of electromagnetic radiationsuch as radio waves.

6. Electrical Discoveries • In nature, electricity occurs only rarely • In some animals • Lightning • In the search to create electrical energy, scientists discovered that electrical and magnetic fields are related. • A magnetic field near a wire causes electrons to flow in a single direction along the wire because they are repelled and attracted by the poles of the magnet • Electrons flowing along a wire generate a magnetic field • The direction of flow and poles of the magnetic field are related • North/South (N/S) • Positive/Negative (+/-) • Negative also referred to as ‘Ground’

7. Electromagnetism • Current is induced in a wire when passed through a magnetic field • As the polarity of the magnetic field changes, so does the direction of the electric current’s flow

8. Electromagnetism • A magnetic field is generated around a wire when current is passed through it • Note that electrons actually flow from negative to positive, as shown in the figure, although we normally think of current flowing in the other direction

9. Electrical Terms • Electric charge:a property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields. • In electricity, charges produce electromagnetic fields which act on other charges. Electricity occurs due to several types of physics. • Electric field: an especially simple type of electromagnetic field produced by an electric charge even when it is not moving (i.e., there is no electric current). The electric field produces a force on other charges in its vicinity. Moving charges additionally produce a magnetic field. • Electromagnets: electrical currents generate magnetic fields, and changing magnetic fields generate electrical currents

10. Electrical Terms • Electric potential: The capacity of an electric field to do work on an electric charge, typically measured in volts • Electric current: The movement or flow of electrically charged particles, typically measured in amperes (amps) • Electric power: The rate at which electric energy is transferred by an electric circuit. The unit of power is the watt (joules/second) • One volt is one joule per coulomb, and one amp is one coulomb per second.If you multiply these two units, you get joules per second, which is also known as watts, a unit of power. • Coulomb = a unit of electric charge; the charge transported by a steady current of one ampere in one second • Electrical resistance:The opposition to the passage of an electric current through an element. The unit of electrical resistance is the ohm (Ω) • Electrical conductance: The ease at which an electric current passes through an element. . The unit of electrical conductance is the siemens (S)

11. Voltage • Voltage, otherwise known as electrical potential difference or electric tension is the electric potential difference between two points • Voltage is equal to the work which would have to be done against a static electric field to move the charge between two points. • Voltage can be thought of as pressure, or tension • High-tension wires –> high voltage

12. Current • Electric current is a flow of electric charge through a conductivemedium. • What is a conductive medium? • AKA ‘conductor’ • Anything that electrical current passes through

13. Resistance • The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element • Electrical resistance shares some conceptual parallels with the mechanical notion of friction. • The unit of electrical resistance is the ohm (Ω) • All materials show some resistance, except for superconductors, which have a resistance of zero.

14. Conductive Medium What is a conductive medium – aka ‘conductor’? • Anything that electrical current passes through • Some are better than others • Metal wire – good • Water - good (Salt water – better) • Tree limb – not so good • You – not bad (though very painful and potentially fatal) • Things that are not very good conductors are call ‘Insulators’ • Polymers (plastics, vinyl, rubber) • Glass • Wood • Why? • Resistivity – all materials conduct electricity, some have very high resistance and conduct insignificant amounts • The resistance of a material to conducting electricity determines if it is a good conductor or a good insulator • That’s why wires have “Insulation” – it resists conducting current – and protects people and property

15. Power,Energy & Work • Electric power is the rate at which electric energy is transferred by an electric • Electric power, like mechanical power, is the rate of doing work, measured in watts • Electric power is transformed to other forms of power when electric charges move through an electric potential (voltage) difference. • When an electric charge moves through a potential difference, from a high voltage to a low voltage, the potential does work on the charges, converting the energy in the potential to kinetic energy of the charges, or some other form. • This occurs in most electrical appliances, such as light bulbs, electric motors, and heaters; they consume electric power, converting it to mechanical work, heat, light, etc. In electronics these are called passive devices. • If the charges are forced to move by an outside force in the direction from a lower potential to a higher, power is transferred to the electric current. • This occurs in sources of electric current, such as electric generators and batteries.

16. Electrical Components • Power source – origination of electrical energy • Generator - converts mechanical energy to electrical energy • Battery - a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy • Wires – conductors of electrical energy • Loads – consumers of electrical energy • Perform work • Lights • Motors • TVs • iPods • Resistors (switches) – controllers of electrical energy • On/Off • Hi/Lo • Volume (potentiometer – adjustable resistor) • Fuses & Circuit Breakers – safety valves of electrical energy

17. Hydraulic Analogy • Electrical theory has similarities to hydraulics • How water flows through the pipes in your home • Disclaimer: Water and electricity DO NOT MIX – fatal

18. Component equivalents • Power source – water tank or pump • Wires – pipes • Loads – consumers of water • Clothes washer • Sprinkler system • Water wheel • Perform work • Resistors (valves) – controllers of water flow • Sink faucet • Fuses & Circuit Breakers – relief valves • On water heaters

19. Hydraulic system

20. Hydraulic->Electrical Concepts

21. Hydraulic Circuit -> Electrical Circuit

22. Ohm’s Law • Fundamental law of all electrical theory • Georg Simon Ohm - Using equipment of his own creation, Ohm found that there is a direct proportionality between the potential difference (voltage) applied across a conductor and the resultant electric current. This relationship is known as Ohm's law. • Ohm's law states that the current through a conductor between two points is directly proportional to the potential differenceacross the two points. Introducing the constant of proportionality, the resistance, one arrives at the mathematical equation that describes this relationship: • Where I = Current (Amps), V = Volts, R = Resistance (Ohms - Ω) I = V/R (Current = Volts/Resistance) • V = IR (Volts = Current * Resistance) • R = V/I (Resistance = Volts/Current)

23. Ohm’s Law • Though not part of the original theory, in later years, we have also attributed the Power factor to Ohm as well. Power is usually abbreviated by (W) and measured in Watts. The formula generally given for Power is: • Where W = Watts, V = Volts, I = Current (Amps) W = V x I (Watts = Volts X Current) • I = W/V (Current = Watts/Volts) • V = W/I (Volts = Watts/Current)

24. Dangers • Too much voltage through conductor that is too small • Reversing polarity in an electric circuit • Connecting ‘+’ terminal of battery to ‘–’ terminal of load • What can this do? • Wires can burst into flames • Insulation and non-conductors can melt from heat • Electronic components and motors may “Release the magic smoke” • - and no longer work, aka “bricked”

25. Types of Electrical Systems • Alternating Current (AC) • The flow of electric charge periodically reverses direction • Direct Current (DC) • The flow of electric charge is only in one direction • Flow? • The flow of electrons through a conductor – through a wire • One direction or both directions along a wire

26. Types of Electrical Systems

27. Alternating Current • What you have in your home, school, mall, offices • Just about everything you come in contact with that is fixed in place • i.e.: A building • High voltage • 120 Volts most common (in U.S.) • 240 Volts also used for dryers, air conditioners, electric stoves • Common in much of world • Produced at power plants • Not used in Robotics • Due to generation technique and nature of electronic components • All use Direct Current

28. AC Current Flow

29. Why Alternating Current? • Primary benefit is transmission over long distances • Direct current has limitations on transmission distances • Enabled societies to distribute electricity to homes, factories, businesses

30. AC Pioneers • Sebastian Ziani de Ferranti • Designed first truly modern power station in London – completed in 1891. • Supplies high-voltage AC power that was then "stepped down" for consumer use on each street. • This basic system remains in use today around the world. • Many homes all over the world still have electric meters with the Ferranti AC patent stamped on them

31. AC Pioneers • Nikola Tesla • Developed ways to commercially harness AC • It travels farther without losing energy • Can transfer different amounts of power • Instead of applying the magnetism along the wire steadily, he used a magnet that was rotating. • When the magnet was oriented in one direction, the electrons flowed toward the positive, but when the magnet's orientation was flipped, the electrons turned as well. • AC generators gradually replaced Edison's DC battery system because AC is safer to transfer over the longer distances and can provide more power. • Nearly 300 patents – including transformers and motors. • Sold to George Westinghouse - commercial pioneer • Conducted ground-breaking experiments in Colorado Springs

32. AC Power W = V x I (Watts = Volts X Current) • I = W/V (Current = Watts/Volts) • V = W/I (Volts = Watts/Current) • Hair Dryer • Uses 1000 Watts (written on label) • AC Voltage @ Home = 120 Volts • Current = ? Amps • I = 1000 watts / 120 volts • I = 8 Amps • Typical home circuits are rated at 15 amps • Multiple outlets on each circuit • A hair dryer uses more than half of that available current • Other outlets on same circuit would be limited on their amp usage • If combined loads on that circuit exceed 15 amps the circuit breaker would flip and power would be cut • Circuits are built for the load they are expected to carry – determined by a ‘Power budget’ • These circuits are typically built such that the load experienced rarely exceeds 80% of the rated current • 15 amps * .80 = 12 Amps

33. Direct Current • The unidirectional flow of electric charge • Direct current is produced by sources such as batteries, thermocouples, solar cells • The first commercial electric power transmission(developed by Thomas Edison in the late nineteenth century) used direct current. • Because of the significant advantages of alternating current over direct current in transforming and transmission, electric power distribution is nearly all alternating current today • Used in Robotics

34. DC Flow

35. DC Flow

36. Why Direct Current? • Direct current is used to charge batteries • Is the power source for nearly all electronic systems • Lower voltages – 12 Volts typical • However other voltages are common • 5 • 24 • 48 • FIRST Robotics robots use 5, 12 and 24 volts on the robot • Voltage changes handled by on-board transformers • Lower power needs of electronics • Simpler • Portable • Used in robotics, cars, TVs, iPods, Computers, Tools - Mars rovers

43. DC Power W = V x I (Watts = Volts X Current) • I = W/V (Current = Watts/Volts) • V = W/I (Volts = Watts/Current) • Robot battery provides 12 volts of power and 17 amp hours • CIM Motor is rated at maximum power of 68 amps • Free current: 2.7 amps • Stall current: 133 amps • How much power does the motor use at maximum power in one hour? • Draws 68 amps • Driven by 12 volts • W = 68 * 12 = 816 watts • How fast will the battery drain at this rate? • Calculate the energy the battery has • E= (amp hour rating) x (average voltage of the battery) x (3600 seconds per hour) • E = 17 Ah * 12 volts X 3600 sec/hr = 734,400 joules  energy within the battery • Calculate the drain time • Time (T) = (energy stored in the battery) / (total power drain) • T = 734,400 joules / 816 watts = 900 seconds = 15 minutes

44. Differences between AC & DC • The amount of energy that each one can carry • AC can carry significantly more energy than DC • How the power is generated • Rotating magnets vs. fixed magnets • Chemical ‘generation’ – batteries • Batteries are DC power sources • Batteries are designed to produce only one voltage level • AA, AAA, D, 12-Volt • Voltage of direct current cannot travel very far until it begins to lose energy • AC voltage from a generator in a power plant can travel very far • And it ca be bumped up or down in strength by another mechanism, called a transformer • Illustration of current flow differences between AC & DC • http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html

45. Differences between AC & DC

46. AC Power Sources

47. DC Power Sources

48. Power Devices • Transformers • Converters • Inverter

49. Transformers • Transformers are used wherever an electrical voltage needs to be increased or decreased. • Commonly seen on electrical poles. • A power plants produces electricity at a very high voltage so that it can travel great distances. • The voltage must be reduced, however, before the electricity reaches homes and other buildings that use it to power appliances, machinery and other devices.

50. Converters • AC adapter , AC/DC adapter, AC/DC converter • Converts AC power to DC power • Uses a transformer to convert the voltage from the wall outlet (mains) to a different, usually lower, voltage. • Uses a rectifier to convert alternating voltage to a pulsating direct voltage