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DC MOTORS

DC MOTORS. Weicong Chen Kelsey Rosenthal Bochao Wang. Outline. Theory EM Fields Brushed and Brushless motors Applications Torque and Speed Types of Motors Interfacing H bridge PWM. Outline. Theory EM Fields Brushed and Brushless motors Applications Torque and Speed

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DC MOTORS

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  1. DC MOTORS Weicong Chen Kelsey Rosenthal Bochao Wang

  2. Outline Theory • EM Fields • Brushed and Brushless motors Applications • Torque and Speed • Types of Motors Interfacing • H bridge • PWM

  3. Outline Theory • EM Fields • Brushed and Brushless motors Applications • Torque and Speed • Types of Motors Interfacing • H bridge • PWM

  4. What's a DC motor? • Armature • Commutator • Brushes • Axle • Magnet • Power supply http://www.cvel.clemson.edu/auto/actuators/motors-dc.html

  5. Some Basic Theory • Lorentz force • Force on a current carrying wire http://en.wikipedia.org/wiki/File:Regla_mano_derecha_Laplace.svg

  6. Brushed DC electric motor http://www.tutorvista.com/content/physics/physics-ii/electricity/electric-generator.php

  7. Advantage of brushed DC motors • Low initial cost (Most important!) • High reliability • Simple control of motor speed

  8. Brushless DC motor (BLDC) • "Turn the motor inside out" • Hall Sensor

  9. How it works? http://openbookproject.net/electricCircuits/AC/AC_13.html

  10. Video http://www.youtube.com/watch?v=aBsM6LXZ2-M&context=C4d12785ADvjVQa1PpcFPT8HbM3n_r4BWkonvXmhjU1AFbCAlV5MQ=

  11. Advantages of brushless DC motors • High reliability • Long life span • No brush sparking • Responsiveness & Quick acceleration • High operating speed • High efficiency

  12. Outline Theory • EM Fields • Brushed and Brush-less motors Applications • Torque and Speed • Types of Motors Interfacing • Hbridge • PWM

  13. Torque to Speed Conversion Basic Eq: T1 *S1=T2*S2 Gear Ratios: T1/T2=D1/D2 Efficiency losses: Eff=gear type efficiency^(# of gears-1)

  14. Types of DC motors: Plug and play • Brushed • Cheapest $1-$100 • Easy to Work With

  15. Types of DC motors: Stepper • Brushless • Discrete Steps ->Known Speed • Driving Modes • Wave Drive • Full Step Drive • Half Step Drive

  16. Types of DC motors: Servo • Precision Angle Control • Can Modify for Full Rotation • Most expensive $5-$3,795

  17. Outline Theory • EM Fields • Brushed and Brush-less motors Applications • Torque and Speed • Types of Motors Interfacing • Hbridge • PWM

  18. H bridge • Definition: An electronic circuit that enables a voltage to be applied across a load in either direction • Problems: • what if the car needs to go backwards • processor is not strong enough to drive motors • Solution: H bridge!

  19. Working principle • Reverse the polarity • Brake the motor

  20. Two examples S1 and S4 are closed S2 and S3 are closed Motor moves right Motor moves left S1 S3 S1 S3 S2 S4 S2 S4 http://en.wikipedia.org/wiki/File:H_bridge_operating.svg

  21. How to drive the DC motors • DC motors are power consuming • We usually need an extra driver: L293D chip • L293D: dual H bridge • 16 Pins • control 2 DC motors • 2 inputs & 2 outputs for each motor https://www.google.com/search?hl=en&q=L293D+figures&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.,cf.osb&biw=1843&bih=965&wrapid=tlif133286699490210&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=yu9xT_m6JoLlqQGrnsCXDA

  22. Continue Truth table • Set the enable to high(+5V) • Connect Vs and Vss to 5V & all GNDs to 0V • Use C program to program the MCU

  23. SmartFusion There is a TRINAMIC's TMCM-AC-840 Daughter Board to connect to our Eval kit http://www.actel.com/documents/partners/TRINAMIC_TMCM-AC-840_Demo_UG.PDF

  24. PWM • Known as Pulse Width Modulated Signals • Used to deliver a variable amount of energy to an end system http://en.wikipedia.org/wiki/File:Duty_cycle_general.svg

  25. How to work with DC motors • Say we need 3V DC voltage for a motor, but there is no such source. • Use PWM with high voltage 5V and low 0V, and duty cycle 60%. • Then, we get 5 × 60% = 3V ! • However, the frequency need to be high so the motor won't go step by step.

  26. Questions?

  27. Sources Gears and motor type information http://www.societyofrobots.com Motor Prices from The Robot Shop DC motor interfacing http://www.8051projects.net/dc-motor-interfacing/l293d-interfacing-with-microcontroller.php H bridge http://embedded-lab.com/blog/?p=1159 SmartFusion http://www.actel.com/products/hardware/devkits_boards/smartfusion_dmc.aspx

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