Today we will get closer look at quadcopter batteries for multirotor devices with emphasis on typical 220″ fpv quadcopter. To complete this task we will go through available technical online documentation on this matter to get closer idea on how battery works and try to implement those functionality gradually to Quadsimu existing logic.
I know that it may sound trivial at the first time to talk about how battery is working. We all know the basics of this matter. Although as always once we start thinking about it more depthly this become more complicated. At this stage we looking for main principles to extend our understanding about batteries for fpv quadcopters. So let’s do it!
From Babylon to Present time. Archeological evidence suggests the Babylonians were the first to discover and employ a galvanic technique in the manufacturing of jewelry by using an electrolyte based on grape juice to gold-plate stoneware. Today we describe a battery as a device that converts chemical energy into electrical energy and vice versa.
Volta discovered in 1800 that certain fluids would generate a continuous flow of electrical power when used as a conductor. This discovery led to the invention of the first voltaic cell, more commonly known as battery. Volta learned further that the voltage would increase when voltaic cells were stacked on top of each other.
Unmanned aerial vehicles (UAVs) and drones come in all sizes, ranging from hand-launched micro-UAVs to large-scale versions that utilize jet propulsion, internal combustion engines, or electric motors. When it comes to in micro-UAVs and smaller format UAVs, the most common method power are Lithium-ion (Li-ion) battery configurations that power the electric motors. Common requirements for quadcopter batteries include high energy/weight ratio, high discharge rates, resilience to shock and vibration, and fuel gauging to indicate remaining mission time.
Li-ion cells come in three basic form factors:
- Prismatic (rectangular brick shape),
- Flat Lithium polymer cells.
The most commonly used Li-ion cell is the cylindrical 18650 cell, which utilizes a steel or aluminum can. Prismatic or brick-shaped cells are available in a myriad of rectangular sizes, and are packaged in a metal can. Lithium Polymer (Li-Po) cells, sometimes called laminate cells, can be encased in flexible aluminum foil laminate pouches that are just 0.1 mm thick, versus the 0.25 to 0.4 mm thick metal cans traditionally used with cylindrical or prismatic cells. The lighter packaging of the Li-Po cell, makes it is the cell of choice for most quadcopter batteries manufacturers.
LiPo batteries are fast approaching the energy density of cylindrical cells. Their compact, light-weight format makes them ideal for a wide range of applications from mobile computing to aerial vehicles.
- High Discharge Lithium polymer ( LiPO ) 3.7V per cell (S),
The total voltage of a battery is determined by the number of cells. To calculate the total voltage, you take the number of cells in series, and multiply by 3.7V. So a 4S battery pack will have 4 cells in series, so its total voltage is 4 x 3.7 = 14.8V.
A voltage sag is a short duration reduction in rms voltage which can be caused by a short circuit, overload or starting of electric motors. A voltage sag happens when the rms voltage decreases between 10 and 90 percent of nominal voltage for one-half cycle to one minute. Some references defines the duration of a sag for a period of 0.5 cycle to a few seconds, and longer duration of low voltage would be called a “sustained sag”.
Battery capacity is a measure in either watt-hours (Wh), kilowatt-hours (kWh), or ampere-hours (Ahr). The most common measure of battery capacity is Ah, defined as the number of hours for which a battery can provide a current equal to the discharge rate at the nominal voltage of the battery. The unit of Ah is commonly used when working with battery systems as the battery voltage will vary throughout the charging or discharging cycle.
C – rate
C rating is a rating of how quickly energy can be discharged from a battery. In describing batteries, discharge current is often expressed as a C-rate in order to normalize against battery capacity, which is often very different between batteries.
The higher the discharge rate, the lower the capacity. The relationship between current, discharge time and capacity for a lead acid battery is approximated (over a typical range of current values) by Peukert’s law.
E – rate
An E-rate describes the discharge power. A 1E rate is the discharge power to discharge the entire battery in 1 hour. Just like the C rate, the E rate can be expressed as:
- I = Discharge current in Amps,
- M = Multiple or fraction of C,
- C = Numerical value of rated capacity of the battery in ampere – hours (AH),
- n = Time in hours for which rated capacity of battery is declared.
Burts rate would be how long battery can provide stable continuous power while max load occurs. Battery can provide stable energie in maximum load only for short period of time. Providing heavy load over this time will damage battery.
Load or Draw is motors energie consumptions while in operation. To get Battery Management System working in Quadsimu we need to find the current load generated by motors.
W = AV(sqrt 3)
- W – power consumption in watts.
- A – amperes,
- V – volts,
- sqrt 3 is the square root of 33 (about 1.73).
Batteries Management System
The Battery Management System (BMS) is a small circuit board in quadcopter batteries provides for advanced functions such as the fuel gauge, LED drivers, safety protection circuitry, thermal sensing, and a serial data communications bus. Active safety protection circuits are necessary to ensure that the Li-ion battery chemistry is kept in a stable condition. The most basic functions of a BMS are protecting the pack from over-charging, over-discharging, short-circuiting, and limiting the cell temperature if the cells approach thermal runaway limits.
Battery Management System
Quadsimu version 1.3 will attempt to provide pilots with Battery Management System. This system is taking information from quadcopter battery and passing this information on screen display OSD. To recharge battery Quadsimu will provide special Charger Spots to land and do recharge battery. Also the way how you will tread battery will have impact in the future on Safety score in “Pilot Status”. Quadsimu v.1.3 BMS will provide you with info such as:
- State Of Charge
- Cells Number
This is a critical design consideration for UAV LiPo packs, since they usually have high discharge rates. These high discharge rates are likely to increase the cell temperature and cause the cells to swell.
Critical features for UAV batteries are the pack’s ability to monitor its state-of-charge, accurately predict its remaining run-time, and communicate its operational status to the UAVs main system. This state-of-charge data is communicated over a serial communication bus to the UAVs main system, which is then wirelessly communicated back to the UAV operator.
- Capacity (mAh),
- Alarm (%),
- Discharge (C) Rate,
- Charge Rate.
Typical requirements for UAV batteries include high energy/weight ratio, high discharge rates, resilience to shock and vibration, and fuel gauging to indicate remaining mission time. For micro-UAVs and smaller-format UAVs, manufacturers typically prefer Li-Po cells as the foundation for their battery packs. The remaining features, like cell chemistry and enclosure type, are typically derived from the use profile and mission type for that specific UAV.
Upcoming version 1.3 of Quadsimu FPV Quadcopter Simulator will provide presented features to play with.
The update 1.3 for QS is not only about quadcopter batteries, see Quadsimu plans and updates page to find more details about what is coming. The next round of improvements for this component will supply:
- Temperature grow and detection,
- Burst rate,
- Number of cells,
- Battery Damage.
- Design Essentials – https://www.machinedesign.com/motion-control/design-essentials-uavs-and-drones-batteries-are-included
- PVEducation – https://www.pveducation.org/pvcdrom/battery-characteristics/battery-capacity
- A Guide to Understand Battery Specification* – https://web.mit.edu/evt/summary_battery_specifications.pdf
- Getfpv – https://www.getfpv.com/learn/new-to-fpv/all-about-multirotor-fpv-drone-battery/
- Wikipedia – https://en.wikipedia.org/wiki/Voltage_sag