1. Computer Vision Group Prof. Daniel Cremers Autonomous Navigation for Flying Robots Lecture 4.1: Motors and Controllers Jürgen Sturm Technische Universität München

2. DC Motors  Stationary permanent magnet  Electromagnet on axis induces torque  Split ring + brushes switch direction of current  Maybe you built one in school Jürgen Sturm Autonomous Navigation for Flying Robots 2 http://www.hometrainingtools.com/dc-motor-kit/p/EL-KIT02/CC BY SA by Wapcaplet http://en.wikipedia.org/wiki/File:Electric_motor_cycle_2.png http://www.seeedstudio.com/depot/bitcraze-m- 64.html?ref=side

3. Control of DC Motors  More power = faster rotation  How to modulate power using a digital signal?  Pulse width modulation (PWM)  Duty cycle = proportion of on time vs. period Jürgen Sturm Autonomous Navigation for Flying Robots 3 75% 50% 25% duty cycle period 5V 0V0V

4. Brushless Motors  Electromagnets are stationary  Permanent magnets on the axis (either inside or outside)  Three coils (or more)  No brushes (less maintenance, higher efficiency) Jürgen Sturm Autonomous Navigation for Flying Robots 4 https://www.hobbyking.com/hobbyking/store/ __25556__AX_2810Q_750KV_Brushless_Quadcopter_Motor.html N S

5. Brushless Controllers  Typically one microcontroller per motor  Generates PWM signal for the three motor phases  AC signal converter (MOSFET) to convert PWM to analogue output  Measure motor position/speed using back-EMF Jürgen Sturm Autonomous Navigation for Flying Robots 5 http://en.wikipedia.org/wiki/File:ESC_35A.jpg A-B B-C C-A A B C

6. I 2 C Protocol  Serial data line (SDA) + serial clock line (SCL)  All devices connected in parallel  7-10 bit address, 100-3400 kbit/s speed  Communication between motor controller and autopilot Jürgen Sturm Autonomous Navigation for Flying Robots 6 http://en.wikipedia.org/wiki/File:I2C.svg http://en.wikipedia.org/wiki/File:I2C_data_transfer.svg

7. Example: Parrot Ardrone Jürgen Sturm Autonomous Navigation for Flying Robots 7 http://droneflyers.com/category/ar_drone/ Source: Parrot Brushless motor 3x AC converters (MOSFET) AVR CPU (8 MIPS) 3 motor phases 1:8.75 gears

8. Lessons Learned  DC motors  Brushless motors  Motor controllers  Ardrone example  Next: How do we generate suitable control signals Jürgen Sturm Autonomous Navigation for Flying Robots 8