For Racing Quadcopter

FPV Application

  Multicopters, especially quadcopters, have fast been gaining popularity as agile camera platforms capable of filming high quality video while hovering and maneuvering in tight spaces. This increase in popularity has come about mainly due to new manufacturing techniques and a reduction in component costs, making this side of the FPV hobby more accessible to a wider audience. In recent years, FPV Multirotor racing has become a very fast growing branch of the RC hobby.

  A single LiPo cell has a nominal voltage of 3.7V. To clarify, the nominal voltage is approximately the average of the full charge of 4.2V/cell, and the minimum safe charge of 3.0 V/cell. For the mathematically inclined reader, you will notice that 3.7V/cell is not really the average of those two values, but this is what the battery industry uses as a nominal value.

  Nominal LiPo Battery Voltage = 3.7 V / cell

  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 2S battery pack will have 2 cells in series, so its total voltage is 2 x 3.7 = 7.4V. A 3S battery has three cells in series, so its voltage is 11.1V. Quadcopter battery The voltage of a quadcopter battery pack will determine how fast your propellers spin. Brushless motors have a rating designated in units of kV, which effectively means RPM per volt. So the more voltage you have available, the higher the maximum RPM of your quadcopter’s propellers. This can result in more dynamic agility, and faster speeds.

  The battery capacity represents how much power the battery can hold. You can think of this as being the size of your fuel tank. The higher the capacity, the longer you can fly your quadcopter. Battery capacity is measured in units of milliamp hours mAh. If you have a battery with a capacity of X mAh, and you drain X mA, then it will take one hour to drain the battery.

  Voltage is used to measure the charge of a battery because measuring battery capacity is difficult. The amount of energy going into the battery can be measured, but not how much is actually in the battery.

  Before you even think about getting a larger battery for your quadcopter, there are some downsides to batteries with higher capacities. As the battery capacity goes up, so does its physics size, and weight. The extra flying time that you gain from a larger capacity, may be negated by the extra weight. This is also assuming the larger battery will fit in the drone battery compartment.

  The higher capacity battery could also damage your quadcopter. There will be additional heat buildup in the speed control and the motors which could damage these components.

  You may come across a LiPo battery that has the designation of the form xSyP. The xS section represents the number of cells in a string, as was previously mentioned. The yP portion of the designation is the number of parallel strings in the battery. Adding strings in parallel is done to increase the battery capacity.

  The C rating of a LiPo battery is a measure of the safe and continuous maximum discharge current.

   Maximum Discharge Current = C-Rating x Capacity

  For a 1200 mAh 50C battery has an estimated discharge current of 60A. Some batteries come with continuous C rating and higher burst C rating. The burst rating is only applicable for short periods of time, such as 10 seconds, and not continuous. The burst rating would be used in the case where you are accelerating your drone, but not when it is at steady flight speed.

  If the C rating is lower than what your quadcopter needs, the battery will not be able to deliver the current that the motors needs. You will see a sluggish performance since your quadcopter is under powered. Also, you will be degrading your quadcopter battery at a faster rate than normal. There is also a chance the battery could burst into flames. Do not use an undersized batter.

  Having a C rating higher than what your quadcopter needs sounds great, but you will not see any added benefit or performance. All you will be doing is flying with an oversized battery, that will end up reducing your quadcopter’s performance.