Introduction to Electric Power Systems for Multirotor Drones

1. Intro to Electric Power SystemsUnderstanding Electric Power Systemsused in Multirotor Drone Aircraft Presented by: Lucien B. Miller President & ceo Innov8tive designs, inc.

2. Welcome to the Workshop! For a PDF file of todays Workshop Slides: www.innov8tivedesigns.com/interdrone/power-intro.pdf

3. Brief Introduction About Me • President & CEO of Innov8tive Designs, Inc. • Electrical Engineering Degree from University of South Florida • Commercial Multi-Engine Instrument Pilots License, CFI, CFII, GSI • AMA Member since 1976 • Member of AMA sUAS integration Council • Founding member of SOAC (Society of Aerial Cinematography) • Host of All Things That Fly RC Podcast Show • Contributing Editor for Fly RC, Heli Pilot, Robot and Multirotor Pilot

4. Multirotors come in all Shapes and Sizes Tri-Copter Quad-Copter Hex-Copter X-8 Octo-Copter Y-6

5. But they ALL have one thing in common An Electric Power System Without a Power System, your multirotor is nothing more than an interesting conversation piece sitting on the corner of your desk

6. Power System Knowledge and Understanding • Proper selection of Power Systems is Essential for good operation • Understanding each of the components is vital for proper use • Good soldering technique is something that you will have to learn • There are certain tools that are “Must Haves” for your field kit • Safe charging, discharging and storage of batteries is crucial • Routine maintenance can eliminate most problems in the field • Understanding how power systems work is very important

7. What Makes Up a Power System? Battery Speed Controller Motor Propeller

8. Power System Component Details • Each component of a power system has specifications • These specifications give operating limits for each part • Proper understanding of these parameters is a must • Exceeding a components ratings will cause a failure • Proper de-rating of component specs increases lifespan • Mil-Spec: 50% de-rating, 80% is good for commercial use • Pushing components to the Max greatly shortens lifespan

9. Batteries • Provide DC Power to run the motors and electronics • Parameters include: Voltage, Capacity & Discharge rate • Lithium Polymer (Li-Po) cells are most common today • High energy densities (150 Watt-Hours per Kilogram) • Require special chargers to prevent damaging cells • Can cause serious fires if over-charged or damaged

10. Battery Voltage • Li-Po cells have important specific voltage parameters • Fully charged, Li-Po batteries measure 4.20 Volts per cell • Under load, they drop down to about 3.70 Volts per cell • The voltage output is fairly flat over the entire discharge • Li-Po batteries are essentially dead at 3.0 Volts per cell • Li-Po’s should be stored at 3.7 to 3.8 Volts per cell no-load • Storing fully charged batteries will greatly shorten their life

11. Battery Voltage Discharge Curve Average voltage level is 3.7 Volts per Cell 3.90 V 3.60 V Dead at 3.00 V

12. Battery Capacity • Typically measured in Milli-Amp Hours or mah • Describes how much stored energy you have in the pack • Larger packs will provide longer flight times • 1000mah = 1 Ah, So a 5000mah pack is a 5.0 Ah pack • Battery weight is directly proportional to capacity size • R-O-T: Li-Po batteries weigh ~ 1 ounce per Ah per cell • A 6-cell 5000mah pack is ~ 6 cells x 5 Ah = 30 ounces

13. Battery Discharge Rate • Also called C-Rate, it describes how fast you can pull energy from a battery pack without damaging it internally • “C” is the Capacity of a cell: In a 5000mah pack, 1C = 5 amps • A 1C discharge rate will completely drain the battery’s stored energy in 1 hour or 60 minutes of use • At 2C the battery will discharge in½hour or 30 minutes • 6C = 10 minutes, 10C = 6 minutes, 15C = 4 minutes, and so on • Most batteries have a C-rating of between 20C and 45C

14. Li-Po Battery Balancing • Balancing means making sure all cells are at the same voltage • Cells are typically connected in Series inside battery packs • Total pack voltage is the sum of the individual cell voltages • Ideally, all the cells in a pack will be at the same voltage • Heating causes inside and outside cells to discharge differently • Over time, this can lead to imbalance between the cell voltages • Changing an unbalanced pack can result in cell damage or fire

15. Li-Po Battery Balancing • Example: 4-cell pack freshly charged 4.20, 4.20, 4.20, 4.20 • Total pack voltage is 16.8 volts when removed from the charger • After many cycles the battery could be 4.30, 4.10, 4.10, 4.30 • Total voltage is still 16.8 volts, but pack is out of balance • If Li-Po cells are charged above 4.30 volts, they will be damaged • If over-charging continues, the pack could catch on fire • Always use a balancing charger when charging Li-Po batteries

16. Li-Po Battery Discharging • Li-Po battery operating range is 3.00 to 4.20 volts per cell • Discharging Li-Po’s below 3.00 volts per cell will damage them • Low Voltage causes electrolyte to gas off and “puff” the cells • Batteries should not be stored fully charged or fully discharged • It is best to store Li-Po batteries at 3.80 to 3.85 volts per cell • Do not charge more packs than you will use on a job • Discharge any pack that will not be used within a week

17. Speed Controllers • Converts DC energy into 3-phase AC to power motors • Allows Flight Controller to vary motor speed • Main ESC Parameters are Max Voltage and Max Current • Should always be rated for the maximum motor current • Require some airflow to keep the internal components cool • Available with special Firmware specifically for Multirotors

18. Other Speed Controller Features • Multirotor specific Firmware allow for faster refresh rates • Response time: 400 Hz and 500 Hz vs common 50 Hz • BEC or No BEC (Battery Eliminator Circuit) • Linear versus Switching type BEC Circuits • PWM (Pulse Width Modulation) Frequency, 8 KHz or 20 KHz • Programmable or upgradable Firmware options

19. Speed Controller Considerations • Should always be sized to exceed Max Motor Current • Normally require soldering to connectors or other wires • Should never be run without a motor attached to output • Do not mix different brands or sizes on the same machine • Make sure all Speed Controllers have the same Firmware • Make sure they are all calibrated the same

20. What a Speed Controller Does .125 mS = 8 KHz 100% Power 75% Power 50% Power 25% Power

21. Brushless Motors • Converts electrical energy into thrust using propellers • Simple design with nothing to wear out other than bearings • 3-phase design is most commonly used for Multirotors • Motors for Multirotors typically spin larger props at low speeds to maximize the efficiency of the propulsion system • 3 main parameters: Motor size, Power rating and Kv Value • Motor size can be confusing due to varying standards

22. Brushless Motors • Most better quality motors use Stator Size to measure motors • Motor power is determined by the Maximum Current Rating • Motor power varies with input voltage, limited by Max Current • A 30 Amp motor: 330 W on 3 cells, 440 W on 4 cells, etc. • The Kv Value tells you how fast a motor will spin • Kv Value has nothing to do with Power Output

23. Stator Size Conventions • Most better quality motors use Stator Size to specify model • Typically a 4-digit number “4020” ie 40mm dia. by 20mm long 20mm Length Motor Stator 4020 Stator 40mm Diameter

24. Motor Size Confusion Hacker A30-XL AXi 2826 Cobra 2826 Thrust 40 Leopard 3542 E-Flite Power-25

25. Brushless MotorPower • Brushless motors can produce large amounts of power • A 1-pound motor can generate up to 5000 watts or 6.5 HP • Power Conversion for Watts to HP, 745.7 Watts = 1.0 HP • R-O-T for estimating Maximum power for unknown motor: Power for a motor = Stator diameter x length x (# of cells/4) • Eg: For a 4020 motor on 6 cells, 40 x 20 x (6/4) = 1200 watts For a 2217 motor on 4 cells, 22 x 17 x (4/4) = 374 watts

26. Propellers • Converts rotational energy from the Motors into thrust • The most critical part of the system to maximize efficiency • Typically measured in inches of Diameter and Pitch eg14x5.5 • Available in Wood, Plastic, Composite and Carbon Fiber • Used in matched pairs of normal and reverse rotation • The most common source of injury in Multirotors

27. Propellers Are Sharp!! • Most propellers have razor thin tips that can cut like a knife • Electric Motors won’t stop spinning until they are shut off

28. Different Propeller Types Carbon Infused Plastic Plastic Carbon Fiber Multi-Blade Wood Folding

29. Prop Efficiency Increases with Size • A propeller is essentially a rotating wing generating lift • Induced drag increases as the square of the airspeed (or RPM) • A larger prop spins slower to produce the same thrust levels • Simply changing props can add 20 to 50% to your flight times

30. Prop Efficiency Decreases with Speed • As a propeller increases in speed, the drag increases • More energy is wasted and prop efficiency decreases • At 40% throttle the prop efficiency is 13 Grams/Watt • At 60% throttle the prop efficiency is 10 Grams/Watt • At 80% throttle the prop efficiency is 7.8 Grams/Watt 13 g/W 10 g/W 7.8 g/W

31. Propellers Should Be Balanced • Unbalanced props cause damaging vibration in a Multirotor • Excessive vibration can destroy sensitive electronics

32. Inspect Props for Damage • Inspect props before flight and look for nicks, scratches or cracks • Losing a prop blade in flight can cause the loss of a Multirotor

33. Final Thoughts About Propellers • A propeller is essentially a rotating wing generating lift • They can be REALLY sharp, so never allow contact with body parts • Choose the right type of prop for the specific type of Multirotor • The best efficiency comes from using larger props at lower RPM’s • Don’t forget to balance your props, vibration kills electronics • Inspect props before every flight and don’t hesitate to change them • Props are like fans, when they quit spinning people start to sweat!

34. Special Tools for Power Systems • A Good Soldering Iron: Lots of solder joints to make on Multirotors • Wattmeter: Essential for measuring current draw and voltage • Digital Volt-Meter: Measures everything to do with electronics • Servo Driver: Allows you to bench test ESC’s without a transmitter • Pulse Meter: Allows you to “See” what your receiver or FC is doing • A 4-cell Ni-CAD pack: For powering Receivers and Flight Controllers • Duct Tape: I mean really, who leaves home without Duct Tape!

35. SolderingIrons • Soldering is a skill that you must master to work on Multirotors • Soldering is actually easy, once you learn a few simple rules • The #1 cause of power system failures is poor solder joints! • You should get a good temperature controller solder station • Use the right size Iron and correct size tip for each application • Seek out the knowledge of others for training and assistance

36. What to Look For in a Soldering Iron • Wattage: 40watts minimum, 60 to 80 watts for larger connectors • Easily interchangeable tips with available spare parts • Output adjustment for setting iron temperature • A solid base for holding your soldering iron between uses • Temperature readouts are nice, but will increase the cost • Portable soldering irons are great for out in the field repairs • Remember that tools are an investment, Buy Quality & Buy it Once

37. Different Soldering Iron Types Adjustable Station Basic Iron Temp Controlled Butane 12V Portable Soldering Gun

38. Different Types of Solder 60/40 Tin-Lead 374˚ F 63/37 Tin-Lead 361˚ F Acid Core Solder ROHS Lead-Free 430˚ F

39. Different Types of Solder Flux Rosin Flux Liquid Rosin Flux Paste Acid Flux Paste Rosin Core Solder

40. Soldering Do’s and Don’ts • Always use a big enough soldering to do the job quickly • If it takes more than 10 seconds to heat up, use a bigger iron • Make sure the iron and parts are clean, and use soldering flux • Pre-tin connectors and wires for the best connections • Always use Rosin Core Solder, NEVER use Acid Core Solder! • Re-tin “Pre-Tinned” wires on ESC’s or Motors before soldering • Keep your iron clean! Wipe it off before every solder joint

41. Wattmeter • Plugs in line between your Battery and Speed Controller • Measures Battery Voltage, Motor Current and Watts of Power • Many will store data internally for later viewing • Some will have a USB interface to connect with a PC • Full feature models will also measure Li-Po battery balance • Relatively low cost item $20 to $60

42. Digital Voltmeter • Digital Voltmeters or DVM’s have a multitude of uses • Virtually all DVM’s measure Volts, Amps, Ohms in many ranges • Some measure Continuity, Test Diodes, Test Transistors & more • Keep one on the bench at home and in the tool box for the field • Check Harbor Freight flyers and get them for free with coupons! • Relatively low cost item $5 to $100

43. Servo Driver • Provides Pulse Signal needed to drive Servos or ESC’s • Allows testing of power systems without using TX & RX • Better models have a digital display to show output pulse width • Typically powered off of the BEC in the Speed Controller • Check for proper calibration of Speed Controller Endpoints • Relatively low cost item $10 to $30

44. Pulse Width Meter • Shows the pulse width coming from Receiver or Flight Controller • Very useful for trouble-shooting Power Systems • Allows you to see whether a Receiver or Flight controller is working properly and sending out the correct signals • Relatively low cost item $20 to $40

45. A 4-cell Battery Pack • Can be Ni-Cad, Ni-MH or Alkaline Batteries • Very useful for trouble-shooting Power Systems • Allows you to set up your flight controller and receiver without needing to plug in your motor batteries or run your BEC circuit • Can prevent serious electrical problems when testing gear • Relatively low cost item $5 to $20

46. Bringing it all Together • Get familiar with your equipment, especially the Power System • Learn how to properly take care of your Batteries • Get a basic understanding of Motors and Speed Controllers • Respect Propellers! They will bite you if you are careless • Learn how to Solder! This is essential for proper maintenance • Get the proper tools for easy trouble-shooting and repairs • Be Safe! Do not become a news headline of what not to do

47. Thanks for Attending the Workshop! For a PDF file of todays Workshop Slides: www.innov8tivedesigns.com/interdrone/power-intro.pdf Other Web Resources Company Website: www.Innov8tiveDesigns.com ATTF Podcast: www.allthingsthatfly.com Lucien’s Blog Site: www.LucienMiller.com Lucien’s Email Address: lmiller@Innov8tiveDesigns.com Drone Information: www.thetruthaboutdrones.com AMA Membership: www.modelaircraft.org