Batteries

Hobby King Zippy 11.1v 30C 3000mAh LiPo Battery

LiPo batteries (short for “Lithium Polymer”) are the latest and greatest when it comes to battery technology.  When considering power to weight ratio, LiPos are far superior compared to NiCad (Nickel-Cadmium) or NiMH (Nickel-Metal Hydride) batteries.

There are several options when choosing a LiPo battery.  The first is the voltage level that the propulsion system runs at.  A single cell LiPo battery outputs 3.7 volts.  To increase the overall voltage, LiPo cells are connected in serial.  Connecting the LiPo cells in serial, cumulatively adds to the overall voltage.  For example, two 3.7 volt LiPo cells will output 7.4 volts and a three LiPo cells will output 11.1 volts and so on.  For Scout, the motors and Electronic Speed Controllers that I have chosen run at 11.1 volts and so I chose 11.1 volt battery.

The second option is capacity.  Capacity is how much power the battery can hold measured in milliamp hours (mAh).  For example, a LiPo battery rated at 1000 mAh will discharge in one hour with a 1000 milliamp load placed on it.  If the same battery had a 4000 milliamp load placed on it, the battery will discharge in 15 minutes.  The higher the capacity of a battery, the longer the flight time, but also the bigger and heavier the battery will be.

The third option is discharge rate.  Discharge rate is how many amps can be discharged at a time.  The discharge rate is multiple of the total capacity of the battery and represented as the “C” rating.  For example, a battery with a capacity of 2000 mAh and a discharge rate of 10C is capable of withstanding 20,000 milliamp or 20 amp loads.

 

Calculate Flight Time of LiPo Battery

Before we can calculate flight time, we need to know the average amperage the quadcopter will draw.  Once we have the average amperage draw we can then calculate flight.

To calculate flight time, take the battery’s capacity in amp hours, then divide that into the average amp draw of the quadcopter and then multiply it by 60.  The total is the flight time in minutes.

For Scout, I chose a 11.1 volt 30C 3000 mAh LiPo battery.  I calculated the average amp draw of Scout to be around 20 amps.  This will give me a flight time of 9 minutes.

Flight Time Calculator

Battery Capacity: mAh
Average Amp Draw: A
Flight Time: Minutes

Battery Charger

LiPo charger needs to be capable of charging a 3-cell battery.  A battery charger capable of balance charging the battery is also recommended.  Balance charging reads the voltage of the individual cells of the battery and charges each cell equally to the other cells.   This feature will increase charging time but will prolong the life of the battery and provide slighter longer flight times.

 

ESC

Castle Creations 35 Amp Brushless ESC

An Electronic Speed Controller, or “ESC” controls the speed of the motor.  ESCs will have a power limit.  The more power an ESC can handle, the larger, heavier and more expensive the ESC will be.  When choosing an ESC, it needs to match or exceed the motor’s peak amperage.  If the peak amperage of the motor is 13 amps, then an ESC rated at 15 amps will be sufficient.  An ESC with a lower rated amperage will overheat and possibly fail.

Some common features of an ESC are a low voltage cutoff.  The low voltage cutoff will cut the power to the motors when the voltage drops to a specific level.  This is a protection feature for LiPo batteries.  If a LiPo battery’s voltage drops below its minimal voltage, it can permanently damage the battery.  The low voltage cutoff protects the battery from dropping below its minimal voltage.

Some ESCs can be programmed to have different throttle responses, adjust the low voltage cutoff limit, reverse the motor’s direction and change the switch rate.