Intro to Electric Power Systems Understanding Electric Power Systems used in Multirotor Drone Aircraft P R E S E N T E D B Y: LUCIEN B. MILLER PRESIDENT & CEO INNOV8TIVE DESIGNS, INC.
Welcome to the Workshop! For a PDF file of todays Workshop Slides: www.innov8tivedesigns.com/interdrone/power-intro.pdf
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
Multirotors come in all Shapes and Sizes Tri-Copter Quad-Copter Hex-Copter Octo-Copter Y-6 X-8
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
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
What Makes Up a Power System? Battery Speed Controller Motor Propeller
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
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
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
Battery Voltage Discharge Curve 3.90 V Average voltage level is 3.7 Volts per Cell 3.60 V Dead at 3.00 V
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 1000 mah = 1 Ah, So a 5000 mah 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 5000 mah pack is ~ 6 cells x 5 Ah = 30 ounces
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 5000 mah 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 in ½ hour 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
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
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
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
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
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
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
What a Speed Controller Does.125 ms = 8 KHz 100% Power 75% Power 50% Power 25% Power
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
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
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 Motor Stator 4020 Stator 20mm Length 40mm Diameter
Motor Size Confusion Cobra 2826 AXi 2826 Hacker A30-XL Leopard 3542 E-Flite Power-25 Thrust 40
Brushless Motor Power 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
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 eg 14x5.5 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
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
Different Propeller Types Plastic Carbon Infused Plastic Carbon Fiber Wood Multi-Blade Folding
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
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
Propellers Should Be Balanced Unbalanced props cause damaging vibration in a Multirotor Excessive vibration can destroy sensitive electronics
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
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!
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!
Soldering Irons 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
What to Look For in a Soldering Iron Wattage: 40 watts 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
Different Soldering Iron Types Basic Iron Adjustable Station Temp Controlled 12V Portable Butane Soldering Gun
Different Types of Solder 60/40 Tin-Lead 374 F 63/37 Tin-Lead 361 F ROHS Lead-Free 430 F Acid Core Solder
Different Types of Solder Flux Rosin Flux Paste Rosin Flux Liquid Rosin Core Solder Acid Flux Paste
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
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
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
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
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
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
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
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