DC Motors and H-BridgesPresented By:

Sean Huang, Daniel Simon, and Scott Smith

[1] [2]1

Presentation Outline

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1. Electric Motors2. A (Brief) Review of E&M Physics3. Brushed DC Motors4. Controlling DC Motors5. H-Bridges6. Brushless Motors and Control7. References and Further Reading

Electric Motors

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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.

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[3]

Many Different Types of Motors

Electric Motors

DC Motors AC Motors

Brushless Motors Brushed Motors

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A (Brief) Review of E&M Physics

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A Brief Review of Ohm’s Law

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Ohm’s Law:V = I * R

I = V / R = 9 / 3000 = 0.003 A = 3 mA

[4]

A Brief Review of Magnets

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N S

A Brief Review of Magnets

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N S

A Brief Review of Magnets

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N SI

A Brief Review of Lorentz Forces

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N SI

F = IL x BLorentz Force:

In which direction is the force?

[5]

A Brief Review of Lorentz Forces

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N SI

F = IL x BLorentz Force:

In which direction is the force?

[5]

Brushed DC Motors

13

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How do Brushed DC Motors Work?

[6]

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How do Brushed DC Motors Work?

[6]

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Commutator Ring

[6]

How do Brushed DC Motors Work?

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Commutator Ring

Brushes

[6]

How do Brushed DC Motors Work?

18[6]

How do Brushed DC Motors Work?

19[7]

How do Brushed DC Motors Work?

How do Brushed DC Motors work?

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Adding additional coils increases motor stability.

[8]

Controlling DC Motors

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Goals:

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1. Be reliable (Doesn’t blow up)

2. Control Speed/Torque

3. Control Direction

One (Naive) Approach

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One (Naive) Approach

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??

One (Naive) Approach

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- Not enough power (usually)

- No directional control

Better Approach

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Better (Dangerous) Approach

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I

Better (Dangerous) Approach

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I

[13]

Better (Dangerous) Approach

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I

[9]

Henry

Better Approach

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- Fixes the power supply problem, but

- Back EMF Sparks

- Still no directional control

Better Approach

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I

[10]

Better Approach

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I

[10]

I

Better Approach

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I

[10]

Better Approach

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I- Doesn’t blow up- Control Speed (PWM)

- Still doesn’t control direction

[10]

H-Bridges

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

36[11]

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

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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

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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”

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0

0

[11]

1

0 1

0

0

0

0

1

1

0

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H-Bridge Hazards (Back EMF)● Sudden change in current creates large voltage on motor

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V -> inf

I -> 0

[11]

0

0

● Diodes create a loop that reduces current change ● Smaller current change means smaller voltage across the motor (no back

EMF)

Flyback Diodes

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I = i

V = v[11][11]

0

1 0

1 0

0 0

0

Controlling Motor Speed with PWM

42[11]

[11]

0

1 0

1 0

0 0

0

[11]

Brushless Motors and Control

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How do Brushless DC Motors Work?

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Switch the position of the magnets and coils.

[8]

Brushless Control

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[12]

Brushless Motors

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Brushed Motors

● Cheap● Easy to use● Requires few wires● Simple control circuitry

● Long lifespan● Very high efficiency● Low noise generation● High power to size

ratio

Recommended Further ReadingBrushed DC Motors: http://pcbheaven.com/wikipages/How_DC_Motors_Work/

Brushless DC Motors: https://www.renesas.com/us/en/support/technical-resources/engineer-school/brushless-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-brushless-dc-motors

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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

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