EGB111FOUNDATION OF ENGINEERING DESIGN Studio Week 8 Machine Elements and Actuators Semester 1, 2015 [Tutor 1] [Tutor 2] [email protected] 1 WEEK 7 REVIEW Lecture (week 7) Machine Elements and Actuators Studio (week 7) Linear dynamics Rotational dynamics Power transfer Efficiency Workshop (week 7) Newton’s second law, transient vs. steady state 2 18 N 3 . t = 1. PLIFT = 5.6 cm 4.096 m or 9. rDRUM = 0.LAST WEEK’S STUDIO WORKSHEET 1. FT = 20.72 s 5.6 N 2.7 W 3. FT = 19. TODAY’S STUDIO Electric motors Gearboxes Bearings Pulleys 4 . motor curves are used As torque required increases: Speed decreases Current required increases Efficiency changes 5 . This is called the nominal voltage.ELECTRIC MOTORS Convert electrical power to rotational power Pin = VI Pout = Tω Motors have a voltage at which they run most efficiently. To describe motor behaviour at nominal voltage. MOTOR CURVE EXAMPLE 6 . ELECTRIC MOTOR UNITS Electric motors: High speed. small torque Usually won’t be provided data in SI units Torque: gcm Speed: rpm 7 . If the input voltage is too far away from the nominal voltage. Nominal voltage The voltage that the motor most efficiently runs at. the motor will be very inefficient. but can be generated provided data.ELECTRIC MOTOR DATA Motor curves generally don’t come with cheap motors. No load speed The motor’s speed when spinning freely Stall torque The maximum torque the motor can provide Maximum efficiency This is where a motor should be operating in a well designed system 8 . MOTOR DATA EXAMPLE 9 . 549. b. Ans: Speed = 12458 rpm. MAX = 0.29 A. output power and efficiency of the motor at maximum efficiency.2 10 . current = 1. Determine the input power.cm) Current (A) 0.36 W. POUT = 26. too powerful for project. Would this motor be good to use for your project? Ans: PIN = 48 W.EXAMPLE MOTOR QUESTION Using the following motor data: a. Nominal voltage No Load Maximum = 12V Efficiency Speed (rpm) 13000 Torque (g. Draw the motor curves for speed and current and find the speed and current for a torque of 50 gcm.6 Stall 10489 - 246 1200 4 17. 11 . use motor curves to predict behaviour Test your motors once you receive them Avoid high voltages and testing close to stall conditions. and design system to operate at maximum efficiency Make sure your motor has data! If operating motor outside of max efficiency conditions.MOTOR SELECTION + DESIGN TIPS Select a motor that is appropriate considering the power requirements. This could burn your motor out. MOTOR TROUBLESHOOTING If a motor needs to move a load faster Increase the voltage Increase the drum size (only if far away from stall conditions) Select a more appropriate motor If a motor is unable to lift a load Increase current limit Decrease the drum size Select a more appropriate motor Use a gearbox 12 . of teeth 13 .GEARBOXES Gearboxes use mechanical advantage to increase torque capability at the expense of decreasing speed Gear ratio = (N2/N1) + (N4/N3) + …… N is no. GEARBOX EXAMPLES 14 . 50.024 Nm.. select GR = 300 (safer to round up).4. Determine the following. 100. 150.22 rad/s. The output of the gearbox is required to provide a torque of 5 Nm. Ans: GR = 260.EXAMPLE GEARBOX QUESTION The motor from the previous example is used at max efficiency (T = 0. …. assuming the gearbox has an efficiency of 80%: a) The gear ratio required by the gearbox b) The output speed from the gearbox c) The gearbox size you’d select if gear ratios were only available in multiples of 50 eg. ω = 4. ω = 1098 rad/s). 15 . BEARINGS Bearings are a machine component that restrain motion to a particular direction and reduce friction in that direction. Bearings must be strong enough to support the moment created by the 0. Highly recommended for designs that require rotating members.5 kg mass as well as the self weight of he crane. 16 . but not well suited to large amounts 17 .PULLEYS Create mechanical advantage by increasing force capability. while decreasing speed capability Good for small amounts of mechanical advantage. then check speed capability Make sure speed isn’t too fast – this will create very large dynamic loads and make the device too difficult to control Select the best gearbox for your application – there are plenty of different sizes and types Use bearings for rotating members Remember to include efficiencies in your calculations Test all components before assembling the device 18 .MECHANICAL DESIGN TIPS Design system for load capability. PROJECT APPLICATION Designs will require at least one motor. 19 . Should be able to design appropriate mechanical systems so that system operates under 10W and moves the object in under a minute. Mechanical advantage will be required since motors can only provide very small torques. WHERE TO PURCHASE COMPONENTS Hobby stores Electronic stores – eg. Jaycar The internet – Little Bird Electronics and Pololu (parts may take 1-2 weeks to be delivered) 20 . TODAY’S STUDIO SUMMARY Electric motors Gearboxes Bearings Pulleys 21 . power. energy Basic circuit analysis 22 . current. have silver sticker Print and bring worksheet! Lecture (week 8) Introduction to electrical energy Studio (week 9) Voltage.COMING UP IN THE NEXT WEEK Workshop (week 8) Motor testing Wear enclosed footwear. resistance. WORKSHEET Complete 5 problems provided Show all working in solutions Include your details Student name Student number Group ID Submit to tutors by end of studio SEMESTER 2. 2014 23 .