300 likes | 650 Views
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
E N D
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 • Types of Motors Interfacing • H bridge • PWM
What's a DC motor? • Armature • Commutator • Brushes • Axle • Magnet • Power supply http://www.cvel.clemson.edu/auto/actuators/motors-dc.html
Some Basic Theory • Lorentz force • Force on a current carrying wire http://en.wikipedia.org/wiki/File:Regla_mano_derecha_Laplace.svg
Brushed DC electric motor http://www.tutorvista.com/content/physics/physics-ii/electricity/electric-generator.php
Advantage of brushed DC motors • Low initial cost (Most important!) • High reliability • Simple control of motor speed
Brushless DC motor (BLDC) • "Turn the motor inside out" • Hall Sensor
How it works? http://openbookproject.net/electricCircuits/AC/AC_13.html
Video http://www.youtube.com/watch?v=aBsM6LXZ2-M&context=C4d12785ADvjVQa1PpcFPT8HbM3n_r4BWkonvXmhjU1AFbCAlV5MQ=
Advantages of brushless DC motors • High reliability • Long life span • No brush sparking • Responsiveness & Quick acceleration • High operating speed • High efficiency
Outline Theory • EM Fields • Brushed and Brush-less motors Applications • Torque and Speed • Types of Motors Interfacing • Hbridge • PWM
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)
Types of DC motors: Plug and play • Brushed • Cheapest $1-$100 • Easy to Work With
Types of DC motors: Stepper • Brushless • Discrete Steps ->Known Speed • Driving Modes • Wave Drive • Full Step Drive • Half Step Drive
Types of DC motors: Servo • Precision Angle Control • Can Modify for Full Rotation • Most expensive $5-$3,795
Outline Theory • EM Fields • Brushed and Brush-less motors Applications • Torque and Speed • Types of Motors Interfacing • Hbridge • PWM
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!
Working principle • Reverse the polarity • Brake the motor
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
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
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
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
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
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.
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