Anatomy of a Quadcopter

Anatomy of a Quadcopter

So just what is a racing drone and what makes it work? I know that when I was first getting into this I thought these machines were sophisticated electronics finally tuned to work together to defy gravity. A black box of technology that mere mortal could never hope to understand. Since then I have learnt that whilst they are sophisticated, they are a lot more approachable and understandable than I thought.

To get a quad in the air you need seven things. To make it FPV you need two more. Let's go through them one by one.

Frame

Obvious really. Without this you just have a bundle of electronics but choosing one can be tricky. Firstly you have a range of sizes to chose from. Something around 250mm (frames are measured diagonally from motor to motor) is a pretty typical race quad size although 210mm and 180mm are becoming popular. A smaller frame means smaller motors and smaller props but we’ll get to those later.

Flight Controller

Let's start right in the middle of the frame with the Flight Controller. This is the brain of the machine. It has built in sensors to measure angles and speeds and runs firmware that knows how to use those measurements to keep the quad in the air by changing the speed of each motor.

ESCs

We’re onto the parts you need four of now. ESCs (or Electronic Speed Controllers) are what take the signals from your Flight Controller and current from your battery and control the speed of each of your motors. Developments in ESC technology like Oneshot125 mean they can react incredibly fast and apply active braking to your motors.

Motors

The engines of your quad, motors vary in size and speed. The size is measured in diameter and the height of the magnets (the stator) so you’ll see things like “2204” and “1806” bandied about. The speed of the motor is also a factor and it's measured in Kv which means 1000 revolutions per minute per volt. 2300Kv is a pretty typical speed and quite impressive when you think that can mean over 30,000rpm!

Propellers

If you have looked around the store here you’ll see there a lot of choice when if comes to props. Even when you know what size you need you still need to decide on the pitch - how titled the blades are which determines how much of a bite they’ll take of the air. 5030 will be a low pitch 5 inch prop, while 5045 will give you much more thrust. Bullnose props are squared off at the end to give even more thrust and then there are tri-bladed props to, you’ve guessed it, give even more thrust. More thrust is great of course but it comes at a price - your motors and ESCs will need to be able to handle the extra current a high thrust prop will draw.

Receiver

This is the small device with one or 2 antenna that sits on your quad and passes commands from your radio to the flight controller. Not that long ago there would be a wire for pitch, roll, yaw, throttle and switch channels but now we tend to use a single cable that carries everything via a method called PPM.

Battery

When looking at a LiPo (the common abbreviation for a Lithium Polymer battery) battery size and weight are obviously important but there are three other numbers to consider that you might not have come across before: The cell count, capacity and discharge rate. For a FPV quad your cell count is going to be 3S or 4S. This is voltage of your battery 4S give your more power and speed but 3S is a good place to start for a beginner. 4S also put more demands on your motors and ESCs. Capacity is how much charge the battery can hold measures in mAh - milliampere hours. The higher the capacity the longer you can fly but the heavier it is. There’s not point in being in the air for 15 mins if it feels like you are flying a bus so we generally keep battery sizes down to 1300-1800mAh on a 200mm or larger frame and around 1000mAh for anything smaller.

That little lot will get you an LoS (line of sight) quad up in the air. If you want to fly FPV, you need to fit two more things:

Camera

While HD cameras like the GoPro, Mobius and RunCam give you a video out feed from their USB ports you don’t want to fly a mini quad with one of these due to latencey. This means the image coming out of the camera is anything us to a second behind what the quad is actually doing. Instead we use simple board cameras. These are effectively repurposed analog security cameras that are very fast and handle extremes of dark and light very well.

Video Transmitter

The final piece of the puzzle. This is the device that takes the signal from the camera and transmits it back to you. You can then view it however you want - typically via a set of video goggles or a ground station comprising a receiver and small screen.

This is a high level overview of what is on a typical mini quad. There are many more bells and whistles you can add but this is the minimum you need to get flying FPV. I hope that's demystified things a little and if you want to know more, check of the rest of the guides on our site.


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