DC Motors and H-Bridges Presented By: Sean Huang, Daniel Simon, and - PowerPoint PPT Presentation

DC Motors and H-Bridges Presented By: Sean Huang, Daniel Simon, and Scott Smith [1] [2] 1

Presentation Outline 1. Electric Motors 2. A (Brief) Review of E&M Physics 3. Brushed DC Motors 4. Controlling DC Motors 5. H-Bridges 6. Brushless Motors and Control 7. References and Further Reading 2

Electric Motors 3

What are Electric Motors? ● Turn electrical energy into mechanical energy. ● Useful in wide range of embedded applications from automotive to medical. ● Vary from extremely complex to incredibly simple. [3] 4

Many Different Types of Motors Electric Motors DC Motors AC Motors Brushless Motors Brushed Motors 5

A (Brief) Review of E&M Physics 6

A Brief Review of Ohm’s Law Ohm’s Law: V = I * R [4] I = V / R = 9 / 3000 = 0.003 A = 3 mA 7

A Brief Review of Magnets N S 8

A Brief Review of Magnets N S 9

A Brief Review of Magnets I N S 10

A Brief Review of Lorentz Forces In which direction is the force? N I S Lorentz Force: F = IL x B [5] 11

A Brief Review of Lorentz Forces In which direction is the force? N I S Lorentz Force: F = IL x B [5] 12

Brushed DC Motors 13

How do Brushed DC Motors Work? [6] 14

How do Brushed DC Motors Work? [6] 15

How do Brushed DC Motors Work? Commutator Ring [6] 16

How do Brushed DC Motors Work? Commutator Ring Brushes [6] 17

How do Brushed DC Motors Work? [6] 18

How do Brushed DC Motors Work? [7] 19

How do Brushed DC Motors work? [8] Adding additional coils increases motor stability. 20

Controlling DC Motors 21

Goals: 1. Be reliable (Doesn’t blow up) 2. Control Speed/Torque 3. Control Direction 22

One (Naive) Approach 23

One (Naive) Approach ?? 24

One (Naive) Approach - Not enough power (usually) - No directional control 25

Better Approach 26

Better (Dangerous) Approach I 27

Better (Dangerous) Approach I [13] 28

Better (Dangerous) Approach Henry I [9] 29

Better Approach - Fixes the power supply problem, but - Back EMF Sparks - Still no directional control 30

Better Approach [10] I 31

Better Approach [10] I I 32

Better Approach [10] I 33

Better Approach [10] - Doesn’t blow up I - Control Speed (PWM) - Still doesn’t control direction 34

H-Bridges 35

H-Bridge Components ● 4 switches centered around a load 4 flyback diodes ● ● Power supply ● Ground [11] 36

Powering the Motor ● Create a path for current to flow through motor ● Switches turned on/off independently using I/O ● If switch is off (open), no current will flow through the switch ● If switch is on (closed), current will flow through the switch ○ Current will flow through the load if the diagonally-paired switches are on simultaneously [11] [11] 37

H-Bridge Hazards (Shoot-through) ● If both switches on one side are on (closed), we’ll get a short circuit ● Can happen when trying to reverse the direction of the motor [11] 38

Hazard Handling ● Delay is present when toggling the switches ● Delay can cause both switches on one side to be on/off simultaneously ● Perform “turn off” before “turn on” 0 1 1 0 0 0 0 0 1 0 1 0 [11] [11] [11] 39

H-Bridge Hazards (Back EMF) ● Sudden change in current creates large voltage on motor I -> 0 0 0 V -> inf [11] 40

Flyback Diodes ● Diodes create a loop that reduces current change ● Smaller current change means smaller voltage across the motor (no back EMF) 1 0 0 0 0 1 0 0 V = v [11] [11] I = i 41

Controlling Motor Speed with PWM [11] 1 0 0 0 0 1 0 0 [11] [11] 42

Brushless Motors and Control 43

How do Brushless DC Motors Work? [8] Switch the position of the magnets and coils. 44

Brushless Control [12] 45

Brushless Motors Brushed Motors ● Long lifespan ● Cheap ● Very high efficiency ● Easy to use ● Low noise generation ● Requires few wires ● High power to size ● Simple control circuitry ratio 46

Recommended Further Reading Brushed DC Motors: http://pcbheaven.com/wikipages/How_DC_Motors_Work/ Brushless DC Motors: https://www.renesas.com/us/en/support/technical-resources/engineer-school/brushl ess-dc-motor-01-overview.html H-Bridges: http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/ Brushless Control: https://www.digikey.com/en/articles/techzone/2016/dec/how-to-power-and-control-b rushless-dc-motors 47

References [1] DC Motor Photo: https://www.surpluscenter.com/Electrical/DC-Motors/DC-Motors-Face-Mount/1-2-HP-90-Volt-DC-Motor-10-3114.axd [2] H-Bridge Hardware Photo: https://www.robotshop.com/en/l298-dual-h-bridge-dc-motor-controller.html [3] Toy Photo: https://www.walmart.com/ip/Vroom-Rider-Dirt-Bike-Motorcycle-Battery-Powered-Riding-Toy-Orange/33154659 [4] Simple Circuit: https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/simple-series-circuits/ [5] Right Hand Rule Photo: https://en.wikipedia.org/wiki/Lorentz_force#/media/File:Regla_mano_derecha_Laplace.svg [6] DC Motor Still Image and Slow GIF: https://www.explainthatstuff.com/electricmotors.html [7] Alternate Fast DC Motor GIF: https://www.electricaleasy.com/2014/01/basic-working-of-dc-motor.html [8] Better Brushed Motor Photo and Brushless Motor Photo: https://www.renesas.com/us/en/support/technical-resources/engineer-school/brushless-dc-motor-01-overview.html [9] Shock photo: https://dawsonpower.com/blog/2014/09/how-to-help-an-electric-shock-victim/ [10] Flyback Diode Photo: https://resources.altium.com/bill-of-materials-blog/why-you-should-use-a-flyback-diode-in-a-relay-to-prevent-electrical-noise-in-your-circuits [11] H-Bridge Photos and Tables: http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/ [12] Brushless Motor Control:: https://www.digikey.com/en/articles/techzone/2016/dec/how-to-power-and-control-brushless-dc-motors [13] Motor Spec sheet: http://hades.mech.northwestern.edu/index.php/Brushed_DC_Motor_Theory 48