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Micromouse Meeting #3 Lecture #2 Power Motors Encoders

Micromouse Meeting #3 Lecture #2 Power Motors Encoders. Microcontroller – pick one yet? Meet your team Some teams were changed. Previous Stuff. High Level Diagram. Everything needs power Batteries Supply a constant voltage Supply as much current as needed (Ideally). Power. =.

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Micromouse Meeting #3 Lecture #2 Power Motors Encoders

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  1. MicromouseMeeting #3Lecture #2PowerMotorsEncoders

  2. Microcontroller – pick one yet? • Meet your team • Some teams were changed Previous Stuff

  3. High Level Diagram

  4. Everything needs power • Batteries • Supply a constant voltage • Supply as much current as needed • (Ideally) Power = (almost)

  5. Different components require different supply voltages • MCU: ~5V • Gyro: 5V or 3.3V • Supply too little, components don’t work properly • Supply too much, components tend to light on fire Power Regulation

  6. Common voltage divider circuit Power Regulation • Does not work for Micromouse! • Battery voltage decreases as it discharges • If input voltage decreases, output voltage also decreases

  7. These will output a constant voltage even if the input voltage changes • Inside is a complicated mess of transistors and other components • Check datasheet for input voltage range Power Regulation Solution: Voltage Regulator

  8. Convert electrical energy to mechanical energy • Two types: • Brushed • Brushless Motors

  9. Brushed motors take a DC signal • So they are also known as DC motors • Power an inductor to rotate a magnet • Increase the voltage and/or current -> Increase the rotation speed • Reverse the polarity of the input voltage -> Reverse the rotation • Most digital microcontrollers do not have an analog signal output • MCU’s output digital signals – either high or low • How do we control brushed motors? Motors:Brushed

  10. “Fake” analog voltage signal • Square wave with a certain frequency • This can be used to control the speed of a motor Pulse Width Modulation (PWM) • Speed is controlled by rapidly turning the motor on and off • Turn the motor on for a greater fraction of the time to make it rotate faster • The percent of time the PWM signal is on is the duty cycle • 0% duty cycle is same as off all the time; 100% duty is same as on all the time Microcontrollers have libraries/functions that make generating PWM signals really easy

  11. PWM signals can control the speed of the motors easily – cool • Problem: Connect a pin on a MCU to a motor and output a PWM • The motor barely moves • MCUs cannot provide enough current to turn motors at fast enough speeds • Another problem: Microcontrollers cannot invert the PWM signal to rotate the motor in the other direction Motors: Signal Power and turning

  12. Use the PWM signal to control a transistor • The transistor acts as a two-state switch that can handle lots of current • The transistor switches on and off according to the PWM • The motor can be directly powered by the battery, but now its speed can be controlled too Solution: Motor Driver Motors: Driver

  13. Motor driver circuit can pour all the current the battery can supply to the motor – nice • Problem: How can the motor change direction? • Previous circuit allows current to flow in only one direction Motors: Rotation Control

  14. Solution: Use H-Bridges • These use several driver circuits • All contained in an IC Motor Driver: H-Bridge

  15. Turn selected switches on/off to control the current path H-Bridge: Simplified diagram

  16. Datasheet of H bridge describes which pins does what H-Bridge States Close these switches: Motor turns in other direction Close these switches: Motor turns in one direction

  17. Goal is the same as brushed motors: rotate something • Mechanics is different • Multiple inductors attract and repel the magnet • Has more control over DC motors • Controlling brushless motors are more complicated • But fairly easy to do with IC chips/software libraries Motors: Brushless

  18. While the mouse is moving around the maze, it needs to memorize it • It needs some way to tell how many cells it has transversed • So we need some kind of cell counter Cell Counter How does the mouse know going this far is four cells long?

  19. Solution: Rotary Encoder • Attach something to the wheels to count how many times the wheels have turned to get distance • Two major flavors • Optical • Magnets with Hall effect sensor Rotary Encoder

  20. LED shines light through holes in a disc • A detector on the other side counts how many times the disc turns Rotary Encoder: Optical

  21. Attach magnets to a disc • Use Hall effect sensors to detect the changing magnetic field Rotary Encoder: Magnetic

  22. Sensors! • Meet your team if you haven’t already Next

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