Advanced Power System Selection & Maximizing Efficiency in Multirotors

1. Advanced Power System Selection &Maximizing Efficiency in Multirotors Presented By: Lucien B. Miller President & CEO Innov8tive Designs, Inc.

2. Welcome To The Workshop For a PDF file of todays presentation: www.innov8tivedesigns.com/interdrone/power.pdf

3. Welcome To The Workshop

4. Electric Power for R/C Models

5. Some Projects In The Works Scorpion SII-4020-360

6. Some Projects In The Works Scorpion SII-2215-950

7. Some Projects In The Works

8. How do you select a power systemfor a Multirotor Aircraft?

9. Power Systems For Multirotors • For many people, Electric Power Systems are a mystery • With some basic knowledge and understanding, the process used to select an Electric Power System is actually quite easy • Power Systems need to be thought of as a “Total System” • To work together properly, the components must be matched • A properly matched power system can double flight times • An improperly matched system can cause serious problems

10. Basic Power System Overview Battery Speed Controller Motor Propeller

11. 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

12. 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

13. 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

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

15. 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

16. 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 • At 2C the battery will discharge in 30 minutes or ½ hour • 6C = 10 minutes, 10C = 6 minutes, 15C = 4 minutes • Most batteries have a C-rating of between 20C and 45C

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

20. 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

21. 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

22. 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 • 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

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

24. Creating a Matched Power System • Step 2 • Determine System Parameters • Consider Payload • Determine Mission • Adjust System as needed • Recalculate values for new Missions • Select Motors • Select Propellers • Determine Motor Performance • Step 3 • Step 1

25. Initial Starting Parameters • 1000mm Hex Frame with Brushless Camera Gimbal • Panasonic Lumix GH4 Camera for 4K Video • 6-cell Li-Po batteries for powering the multirotor • Desired flight time of 12-15 minutes per charge • Real-Time Telemetry downlink system for framing shots • Retractable landing gear for clear shots • Would like to use 16” or 18” propellers (19.6” Max)

26. Add up the weight of all the component parts for a rough starting point to do your power calculations System Weights Divide total weight by number of motors to determine the thrust needed to maintain a stable hover in flight 8024 ÷ 6 = 1337 grams/Motor

27. Select the Proper Motor • Choose a motor that provides 3 to 4 times the required thrust at full throttle on the desired propeller size • Look for one that can safely run different size props to allow you to adjust the power for varying load conditions • For this specific example: 3 x 1337 = 4011, 4 x 1337 = 5348 • It should develop the required thrust below 50% throttle • Prop Data Charts are an invaluable asset for motor choice!

28. Some Possible Motor Options 4011-5348 gm 234 grams 16x5.5-MR 2634 grams 18x5.5-MR 3194 grams 194 grams 16x5.5-MR 3060 grams 18x5.5-MR Too Big 273 grams 16x5.5-MR 4760 grams 18x5.5-MR 5799 grams 342 grams 16x5.5-MR 4692 grams 18x5.5-MR 5826 grams

29. We are looking for desired thrust of 4011 to 5348 gms On a 16 inch prop APC 16 x 5.5 gives 4760 grams of thrust This is 3.56 times the required 1337

30. We are looking for desired thrust of 4011 to 5348 gms On a 16 inch prop APC 16 x 5.5 gives 4760 grams of thrust This is 3.56 times the required 1337 Also notice the APC 18 x 5.5 prop can be used, 5799 grams of thrust, which is equal to 4.34 times the required hovering thrust

31. Other available data from this chart The Max motor current is 54 amps We will use a 60 Amp ESC The motor weight Is 273 grams This is very close to our 275 gm estimate

32. Now that a motor has been selected,we can look at the performancedata for a specific prop on this motor

33. Propeller Performance Data

34. Shows the thrust level of a Motor & Prop as a function of throttle position Thrust vs Throttle This curve is a square function, but it is fairly linear between 40% and 80% throttle This graph is used to determine the throttle level required to produce the necessary thrust

35. Shows the current draw of a Motor & Prop as a function of throttle position Current vs Throttle This curve is a cubic function that rises rapidly above the 40% throttle level This graph is used to determine how much current each motor pulls to produce the required thrust

36. Shows how fast the prop spins as a function of throttle position RPM vs Throttle This curve is fairly linear from 10% to 90% throttle for most ESC’s This graph can be used to determine how fast the prop will spin, to see if the Max RPM spec is exceeded

37. Shows how many grams of thrust are produced for each watt of input power Efficiency vs Throttle This curve usually peaks at 20% power, and drops in a linear manner to 80% power This graph can be used to compare different brands of props to determine the highest thrust efficiency

38. Step By Step Procedurefor Calculating the Performanceof a Multirotor Power System

39. Determine the throttle level required to make enough thrust to hover the multirotor Step 1: 1337 gm = 47.2 oz Draw a line from the thrust axis to the thrust curve Draw a line from the thrust curve to the throttle axis 45% Read the throttle level

40. Determine the current draw of each motor in a hover Step 2: Start from the bottom of the current chart at the 45% throttle level 6.5 amps Draw a line from the Throttle Axis up to the current curve Draw a line from the current curve to the Current Axis 45% Read the current level

41. Determine the Propeller Speed if desired Step 3: Start from the bottom of the current chart at the 45% throttle level 4200 Draw a line from the throttle axis up to the RPM curve Draw a line from the RPM curve to the Speed axis 45% Read the Prop Speed

42. Determine the Propeller Efficiency if desired Step 4: Start from the bottom of the current chart at the 45% throttle level 9.4 Draw a line from the Throttle Axis to the Efficiency curve Draw a line from the Efficiency curve to the Efficiency axis 45% Read the Prop Efficiency

43. Summarizing the Information • We chose the Cobra CM-4515/18 435 Kv Motor • With the APC 16x5.5-MR prop, this motor will make 1337 gm of thrust at 45% power, pulling 6.5 amps of current on 6 cells • In a stable hover, the props will be spinning at 4,200 RPM • The overall system efficiency is 9.4 grams of thrust per watt • We can now calculate flight times and check battery size

44. Calculating Flight Time • 6 motors at 6.5 amps each equals 39 amps total in a hover • A pair of 6-cell 5000 mah batteries = 10 Ah of total capacity • Discharge rate = Current ÷ Battery Size, 39 A ÷ 10 Ah = 3.9C • Flight time = 60 minutes ÷ C-rate, 60 ÷ 3.9 = 15.4 minutes • This would drain the battery completely, which is not good! • Appling 80% de-rating factor: 15.4 x 0.8 = 12.3 minutes • This is for stable hovering only, moving around lowers time

45. In a hover at 45% power each motor pulls 6.5 A How maneuvering affects flight time At 55% power each motor will pull 10.5 amps 10.5 amps 8.2 amps 6.5 amps At 50% power each motor will pull 8.2 amps These higher power levels will cut into your flight time 45%

46. Re-Calculating Power Requirements • Taking gentle maneuvering into account, the average current draw of the motors will be closer to 8 amps on average • 6 motors at 8 amps is 48 amps which is a 4.8C discharge • 60 ÷ 4.8C = 12.5 minutes, de-rated by 80% = 10 minutes • Accounting for light maneuvering we can fly for 10 minutes • What do you do if you need to fly longer for a job?

47. Adding Batteries for Extra Flight Time • Adding batteries will increase flight time, but …… • You do not get as much extra time as you might think • Twice as many batteries will not give double the flight time • Extra battery weight make the motors work harder • You eventually reach a point of diminishing returns • You can also gain some efficiency by moving to larger props

48. Re-Calculating With Extra Batteries • Original weight was 8024 gms, with 1600 gms of batteries • Adding 2 more batteries gives 20 Ah capacity and 9624 gms • Each motor needs to make 9624 ÷ 6 or 1604 gms of thrust • The higher thrust levels needed will require more current • Re-running the calculations will give the new flight times

49. Determine the throttle level required to make enough thrust to hover the multirotor Step 1: 1604 gm = 56.6 oz 56.6 oz Using the same method as before the new throttle level goes up 45% to 50% to maintain a stable hover

50. Determine the current draw of each motor in a hover Step 2: Start from the bottom of the current chart at the 50% throttle level 8.2 amps Again, using the method as before the new hover current is 8.2 amps per motor