EGB111 Foundation of Engineering Design

EGB111 Foundation of Engineering DesignSemester 1, 2015[Tutor 1][Tutor 2]enquiries.egb111@qut.edu.au1Studio Week 8Machine Elements and Actuators1WEEK 7 REVIEWLecture (week 7)Machine Elements and ActuatorsStudio (week 7)Linear dynamicsRotational dynamicsPower transferEfficiencyWorkshop (week 7)Newtons second law, transient vs. steady state

2Last Weeks studio WorksheetFT = 19.6 NPLIFT = 5.7 WrDRUM = 0.096 m or 9.6 cmt = 1.72 sFT = 20.18 N3TODAYS STUDIOElectric motorsGearboxesBearingsPulleys4Electric motorsConvert electrical power to rotational powerPin = VIPout = TMotors have a voltage at which they run most efficiently. This is called the nominal voltage.To describe motor behaviour at nominal voltage, motor curves are usedAs torque required increases:Speed decreasesCurrent required increasesEfficiency changes5Motor curve example6

Electric motor unitsElectric motors: High speed, small torque

Usually wont be provided data in SI units

Torque: gcm

Speed: rpm7Electric motor dataMotor curves generally dont come with cheap motors, but can be generated provided data.Nominal voltageThe voltage that the motor most efficiently runs at. If the input voltage is too far away from the nominal voltage, the motor will be very inefficient.No load speedThe motors speed when spinning freelyStall torqueThe maximum torque the motor can provideMaximum efficiencyThis is where a motor should be operating in a well designed system8Motor Data Example9

Example motor questionUsing the following motor data:Determine the input power, output power and efficiency of the motor at maximum efficiency. Would this motor be good to use for your project? Ans: PIN = 48 W, POUT = 26.36 W, MAX = 0.549, too powerful for project.Draw the motor curves for speed and current and find the speed and current for a torque of 50 gcm. Ans: Speed = 12458 rpm, current = 1.29 A.

10Nominal voltage = 12VNo LoadMaximum EfficiencyStallSpeed (rpm)1300010489-Torque (g.cm)-2461200Current (A)0.6417.2Motor selection + design tipsSelect a motor that is appropriate considering the power requirements, and design system to operate at maximum efficiencyMake sure your motor has data!If operating motor outside of max efficiency conditions, use motor curves to predict behaviourTest your motors once you receive themAvoid high voltages and testing close to stall conditions. This could burn your motor out.

11Motor troubleshootingIf a motor needs to move a load fasterIncrease the voltageIncrease the drum size (only if far away from stall conditions)Select a more appropriate motorIf a motor is unable to lift a loadIncrease current limitDecrease the drum sizeSelect a more appropriate motorUse a gearbox

12Gearboxes13

Gearbox examples14

Example gearbox questionThe motor from the previous example is used at max efficiency (T = 0.024 Nm, = 1098 rad/s). The output of the gearbox is required to provide a torque of 5 Nm. Determine the following, assuming the gearbox has an efficiency of 80%:The gear ratio required by the gearboxThe output speed from the gearboxThe gearbox size youd select if gear ratios were only available in multiples of 50 eg. 50, 100, 150, ..

Ans: GR = 260.4, = 4.22 rad/s, select GR = 300 (safer to round up).15BearingsBearings are a machine component that restrain motion to a particular direction and reduce friction in that direction.Highly recommended for designs that require rotating members. Bearings must be strong enough to support the moment created by the 0.5 kg mass as well as the self weight of he crane.

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PulleysCreate mechanical advantage by increasing force capability, while decreasing speed capabilityGood for small amounts of mechanical advantage, but not well suited to large amounts17

Mechanical design tipsDesign system for load capability, then check speed capabilityMake sure speed isnt too fast this will create very large dynamic loads and make the device too difficult to controlSelect the best gearbox for your application there are plenty of different sizes and typesUse bearings for rotating membersRemember to include efficiencies in your calculationsTest all components before assembling the device18Project ApplicationDesigns will require at least one motor.Mechanical advantage will be required since motors can only provide very small torques.Should be able to design appropriate mechanical systems so that system operates under 10W and moves the object in under a minute.19Where to purchase componentsHobby stores

Electronic stores eg. Jaycar

The internet Little Bird Electronics and Pololu (parts may take 1-2 weeks to be delivered)20TODAYS STUDIO SUMMARYElectric motorsGearboxesBearingsPulleys21Coming up in the next weekWorkshop (week 8)Motor testingWear enclosed footwear, have silver stickerPrint and bring worksheet!

Lecture (week 8)Introduction to electrical energy

Studio (week 9)Voltage, current, resistance, power, energyBasic circuit analysis

22WorksheetComplete 5 problems providedShow all working in solutionsInclude your detailsStudent nameStudent numberGroup IDSubmit to tutors by end of studio

23Semester 2, 2014