Chapter 3. Choosing Your Components

So, we've learned about how multicopters fly. We've learned about what's in multicopters. We've even learned a thing or two about safety concerns. Now, let's dive into the process of choosing components for your multicopter. There are a ton of choices, permutations, and combinations available. In fact, there are so many choices out there that it's highly unlikely that two do it yourself (DIY) multicopters are configured alike.

It's very important to note before we start this chapter that this is just one example. This is only an example of the thought process involved. This configuration may not be right for your particular needs, but the thought process applies to any multicopter you may build. With all these disclaimers in mind … let's get started!

What kind of drone should I build?

It sounds obvious, but believe it or not, a lot of people venture into a project like this with one thing in mind: "big!". This is completely the wrong approach to building a multicopter. Big is expensive, big is also less stable, and moreover, when something goes wrong, big causes more damage and is harder to repair. Ask yourself what your purpose is. Is it for photography? Videography? Fun and hobby interest? What will it carry? The example in this book is based on a standard videography drone that carries a camera between 2 and 7 pounds in weight. This covers everything from a camcorder to a small DSLR camera.

How many rotors should it have?

There are many configurations, but three of these rotor counts are the most common: four, six, and eight (quad, hexa, and octo-copters). The knee-jerk response of most people is again "big". It's about balancing stability and battery life. Although eight rotors do offer more stability, it also decreases flight time...

Choosing your airframe

Although we've decided to go with a flat-six airframe, the exact airframe is yet to be decided. The materials, brand, and price can vary incredibly. Let's take a quick look at some specifications you should consider.

Carbon fiber versus aluminum

Carbon fiber looks cool, sounds even cooler, but what is it? It's exactly what it sounds like. It's basically a woven fabric of carbon strands encased in an epoxy resin. It's extremely easy to form, very strong, and very light. Carbon fiber is the material they make super cars, racing motorcycles, and yes, aircraft from. However, it's very expensive and can be brittle if it's compromised. It can also be welded using nothing more than a superglue-like substance known as C.A. glue (cyanoacrylate or Superglue).

Aluminum is also light and strong. However, it's bendable and more flexible. It's less expensive, readily available, and can make an effective airframe. It is also used in cars, racing motorcycles, and aircraft. It cannot...

Delving into camera gimbals

The term gimbal refers to a point of rotation. The purpose of a camera gimbal is to counter the rotation of the multicopter as it tilts for flight by rotating the camera in the opposite direction on the gimbal. This effectively cancels the rotation of the multicopter and stabilizes the camera. The following image illustrates how the camera remains level even while the multicopter tilts:

So, that takes care of pitch and roll … what about yaw? Yaw works a little differently. Some gimbals only stabilize on two axes (pitch and roll) so that FPV (first person view) flyers can tell which direction they are headed. Older 3-axis gimbals left the camera pointed in one yaw direction, no matter where the multicopter was facing. This could be problematic and confusing if it was flying using FPV. It would be like the cockpit of a helicopter pointed north while the rest of the aircraft faced south. Then, do you push the stick forward to go forward? Or would that make you go...

The multicopter brain – the guidance system

All guidance systems work on the same principle. They take in a boatload of positional data, compare the data points, and estimate what the multicopter is doing. Keep this in mind: the guidance system has to guess. The difference between systems is how well they guess and how quickly. They all use the same types of sensors, and the difference between the sensors is their accuracy and speed. These are what you need to consider in a guidance system: accuracy and speed. If a guidance system guesses wrong, you could have a Flip of Death or a fly-away on your hands. First, let's take a look at the types of sensors.

Multicopter guidance system sensor types

Multicopters use a variety of sensors to tell where they are and what they are currently doing. They sample this data anywhere from hundreds to tens of thousands of times a second. Let's take a look at them one by one.

Global Positioning System

Global Positioning System (GPS) is a modern-day wonder that...

The human interface

This is highly subjective. People prefer different radios. One thing is definitely important, use something with a lot of range and fidelity. The old days of analog FM transmitters are over, and they're completely inadequate for our needs. Your transmitter should be digital, reliable, and have a good range.

For these requirements, there are really only two choices: Futaba and Spektrum. For our example, we'll be using a Spektrum system. I've found that the interface on the controller to set up Spektrum is a bit easier. I own both types of radio systems, and in the end, Futaba has sat on a shelf and gathered dust for quite a while.

We'll need at least seven channels on our radio system. A channel is defined as one item of control for our purposes. Our channels will be throttle, yaw, pitch, roll, stabilization mode (GPS on/off, attitude only, and failsafe), flight mode, and camera tilt. We'll get into stabilization modes and flight modes in the next chapter.

This leaves two...

The final component list and cost

Here's what we're looking at (as of May, 2014):

Quantity	Item	Cost
1	Turnigy H.A.L. Multicopter Frame	$63.90
6	Turnigy Multistar 4830-480KV 22-pole motor	$245.94
6	Turnigy Multistar 45-Amp ESC (opto)	$110.76
3	Carbon Fiber 14x7 LH and RH pair propellers	$84.30
4	Zippy Flightmax 4S 8000 mAh battery	$235.20
1	Photoship One mkTR Professional Gimbal with landing gear	$494.94
1	DJI WooKong-M	$1,199
1	Spektrum AR8000 receiver	$129
1	Spektrum DX8 transmitter	$299
	Total cost	$2,862.04

Summary

Wow, what a long journey. Congratulations, you've made it this far! We've learned all about the components of our platform and how to go about choosing them. We've learned about the significance of each part and how to balance power, weight, and flight times. Finally, we've compiled a list of parts to put together our multicopter. This is the same list I used for my Beastcopter Mk VII. It represents about 30,000 USD in investments in parts, upgrades, and learning over many years. Again though, this only represents a thought process, and this particular multicopter may not suit your needs. You now have the knowledge and tools to calculate your own multicopter using your own specifications to custom-tailor your platform for your purpose.

In the next chapter, we'll learn about assembling our multicopter and getting it ready for its maiden flight.