Adding LED Lights to Your Multirotor
Almost everything looks more futuristic with multicolored LEDs attached to it. This is certainly true of multirotor aircraft. But putting LEDs on your multirotor will not only make it look really cool, but also it will serve a practical purpose. When flying, especially when flying at dusk or at night, using multicolored LEDs can help you tell which side of your multirotor is front. For example, on a quadcopter, many pilots mount green LEDs on the front two arms, and red LEDs on the rear two arms. As another example, on my Rotor Bits tricopter I have blue LEDs on the front two arms and green LEDs on the rear arm.
You can use whatever colors you want though, many are available from vendors like HobbyKing:
- Blue: HobbyKing 6LED-BL
- Green: HobbyKing 6LED-GR
- White: HobbyKing 6LED-WH
- Yellow: HobbyKing 6LED-YE
- Red: HobbyKing 6LED-RE
Most LEDs for multirotors come as strips of several LEDs on one small PCB. For example, the LEDs I just listed come as strips of six LEDs. Most of these LED strips are designed to run off 12V, which is the voltage output by most LiPo batteries. We cannot simply plug the LEDs into the battery leads though, because there are two different ways to connect LEDs, in series and in parallel. So which way should the LEDs be wired?
The answer is the LEDs should be wired in parallel. Here’s why:
Series vs. Parallel Wiring for LEDs
When designing electrical circuits with LEDs, there are two characteristics of power supplies (the LiPo battery in this case) that we need to consider: voltage and current. The LiPo batteries used in multirotors, as mentioned above, typically provide 12V. As far as LEDs are concerned, the LiPo batteries are capable of delivering unlimited current. Part of the reason we use LiPo batteries for multrotors is because they are capable of discharging the very large currents required to run the motors. Basically, there is no way you could cram enough LEDs onto your multirotor to overwhelm the battery. For example, the batteries used in the SK450 Dead Cat Quadcopter and Rotor Bits tricopter builds are capable of powering 2,200 LED strips like the kinds listed above.
Anyway, back to the issue at hand, series or parallel? Well, when LEDs are wired in series, the voltage is divided among the LEDs and the current required is equal to the current required by each individual LED. For example, if we wired three LED strips in series, each strip would get (12V/3 =) 4V. This is not enough voltage to run the LEDs. The circuit would only require 20mA, but it does not really matter because the voltage is insufficient to run the LED strips anyway.
When wiring LEDs in parallel, each LED gets the same voltage, and the current required for the circuit is the total of the current required for each LED. So, using the same example, if we wire three LED strips in parallel, each strip will get the full 12V from the battery, more than enough to make the LEDs glow nice and bright. The total current required for the circuit will be (20mA * 3 =) 80mA. This current is no issue at all though for the LiPo battery, which is capable of discharging 550 times that current.
So, this is why we wire LED strips on multirotors in parallel.
LED Wiring with a Receiver-Controlled Switch
Now, we could, as we just discussed, wire the LED strips in series and connect them directly to the battery. This would work really well. As soon as we connected the battery to the multirotor’s electrical system, the LEDs would illuminate and make the multirotor nice and visible from hundreds of feet away.
It is nice, however, to have the ability to switch the LEDs on and off. It is particularly useful to be able to switch the LEDs on and off using the radio transmitter. You might be flying during the daylight and want to turn off the LEDs. You might be flying in a location where you don’t want blinding lights on your aircraft. You might be sending some kind of Morse code signal with your multirotor.
Fortunately, there is a really nice component we can add to the circuit to enable the LEDs to be switched on and off with the radio receiver, a receiver-controlled switch. This is a very simple component. It basically just mirrors the action of a toggle switch on the radio transmitter. One example of a receiver-controlled switch is the HobbyKing 9107000266-0.
Connecting a receiver-controlled switch to the circuit is simple. The LEDs are still wired in parallel as before and the receiver-controlled switch simply goes onto the negative side of the circuit to interrupt the circuit. The switch is also connected to the radio receiver. For more information, check out the Rotor Bits tricopter build.