DC Motors and HBridges Presented By Sean Huang Daniel Simon and Scott Smith 1 2 1 Presentation Outline 2 Electric Motors A Brief Review of EampM Physics Brushed DC Motors Controlling DC Motors ID: 764480
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DC Motors and H-Bridges Presented By: Sean Huang, Daniel Simon, and Scott Smith [1] [2] 1
Presentation Outline 2 Electric Motors A (Brief) Review of E&M Physics Brushed DC Motors Controlling DC Motors H-BridgesBrushless Motors and Control References and Further Reading
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. 4 [3]
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 7 Ohm’s Law: V = I * R I = V / R = 9 / 3000 = 0.003 A = 3 mA [4]
A Brief Review of Magnets 8 N S
A Brief Review of Magnets 9 N S
A Brief Review of Magnets 10 N S I
A Brief Review of Lorentz Forces 11 N S I F = IL x B Lorentz Force: In which direction is the force? [5]
A Brief Review of Lorentz Forces 12 N S I F = IL x B Lorentz Force: In which direction is the force? [5]
Brushed DC Motors 13
14 How do Brushed DC Motors Work? [6]
15 How do Brushed DC Motors Work? [6]
16 Commutator Ring [6] How do Brushed DC Motors Work?
17 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? 20 Adding additional coils increases motor stability. [8]
Controlling DC Motors 21
Goals: 22 Be reliable (Doesn’t blow up) Control Speed/Torque Control Direction
One (Naive) Approach 23
One (Naive) Approach 24 ??
One (Naive) Approach 25 Not enough power (usually) No directional control
Better Approach 26
Better (Dangerous) Approach 27 I
Better (Dangerous) Approach 28 I [13]
Better (Dangerous) Approach 29 I [9] Henry
Better Approach 30 Fixes the power supply problem, but Back EMF Sparks Still no directional control
Better Approach 31 I [10]
Better Approach 32 I [10] I
Better Approach 33 I [10]
Better Approach 34 I Doesn’t blow up Control Speed (PWM) Still doesn’t control direction [10]
H-Bridges 35
H-Bridge Components 4 switches centered around a load 4 flyback diodesPower supply Ground 36 [11]
Powering the Motor Create a path for current to flow through motorSwitches 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 37 [11] [11]
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 38 [11]
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” 39 [11] 0 0 [11] 1 0 1 0 0 0 0 1 1 0 [11]
H-Bridge Hazards (Back EMF) Sudden change in current creates large voltage on motor 40 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 41 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 43
How do Brushless DC Motors Work? 44 Switch the position of the magnets and coils. [8]
Brushless Control 45 [12]
Brushless Motors 46 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 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/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 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