As a quadcopter pilot, it’s important to know when to land as flying too long can result in over-discharging your LiPo battery and even permanently damaging them.
There are many ways to determine the best time to land, in this article we will discuss the pros and cons of these methods and what you should use.
Make sure to check out this article to find out more about how to look after your LiPo batteries.
Checking your battery voltage
The most common way of finding out flight battery level, is battery voltage. There are many ways of measuring battery voltage in a quadcopter.
Land at 3.5V per cell!
- 2S – 7V
- 3S – 10.5V
- 4S – 14V
Using Lipo Battery Voltage Alarm or Buzzer
The most popular choice is using a voltage alarm, which is connected to the balance plug of a LiPo battery. They are cheap, and widely available. The buzzer is triggered when any one cell drops below a set threshold, e.g. 3.5V per cell.
Built-in Voltage Sensor in flight controllers, FPV cameras and OSD
Many flight controller boards, OSD, and even flight controllers these days have built-in voltage sensors (a.k.a VBAT feature), and a low voltage alarm is triggered at a user defined value set in the software.
The biggest problem with voltage is that it goes up and down when the load changes. For example when you do a punch out on your quadcopter, the voltage drops badly, but when you lower your throttle the voltage will quickly recover.
Bad LiPo batteries tend to have worse voltage sag under heavy load, and false alarm might happen a lot with low voltage.
Checking your current
You can measure how much current is being drawn by the quadcopter in real time using a current sensor.
More importantly, you would be able to see how much battery capacity (mAh) has been consumed, and since you know the LiPo battery capacity, you would be able to work out how much capacity is left in the pack exactly.
“mAh consumed” is a much more accurate indicator than voltage to decide when you should land, because it doesn’t fluctuate and with throttle level like voltage.
The 90% rule… Must land when you hit 90% of the capacity! At this point the battery is probably at around 3.5V – 3.6V in theory.
However, you should not rely only on “mAh consumed”, because the data always resets to zero when power is disconnected, or when the FC restarts. This method also only works with fully charged batteries, as you won’t know what the exact initial capacity is on partly discharged batteries.
Therefore It’s best to have both the current sensor and VBAT (voltage sensor) on a quadcopter.
However current sensor might be inaccurate when you first get it, and need some calibration described in this guide.
If you don’t have a current sensor on your quadcopter, you can also set up a “virtual current sensor” as shown in this tutorial.
Using timer to determine when you should land is an extremely primitive method for quadcopter flying, as battery usage will always be different in each flight. The same battery pack might last longer or shorter, depending on how aggressive you are on the throttle stick in that flight.
Timing flights is probably the last resort for me to decide when to land if there is absolutely no other better options.
The Different “Low Voltage Alarms”
There are many different forms of low voltage alarms you can have on your quadcopter.
If you have a buzzer connected to the flight controller, it will beep when voltage is low, or if you use one of those low voltage alarms that goes to the balance plug.
For pilots that fly longer range, one might get into situations where the quadcopter is too far away, and the buzzer on the quad cannot be heard. The best option in this case would be using an OSD to display the voltage on the live-streamed FPV video.
I personally prefer using OSD because I love seeing numbers! I can see what the voltage is and plan my flight better, rather than getting shout at by the buzzer only when voltage is nearly dead.
Similar reason to using the OSD, Telemetry is a great alternative to OSD (and it can also be a backup system that runs in parallel to OSD).
Many radio transmitters like the Frsky Taranis can display battery voltage on the screen. You can even set it up to speak to you what the values are in human voice!
- Dec 2014 – article created
- Aug 2016 – Updated info about telemetry
- Aug 2017 – Updated info about current sensor