The Quadcopter Crash Course

by UAVman  (a.k.a. DeathNinja McSex)

Before I start on what is to be a massive purge of all knowledge I have gained in my obsession-fueled journey, I have to state that that journey was inspired entirely from watching this video: www.youtube.com/watch?v=fyYujjP5J-k  (Link Info)

After watching, I instantly had the urge to build one and hope that by inviting as many people as possible to view it, I can infect more people with this obsession as (from my perspective) it is a healthy obsession, being that it's hard to do this while sitting in a basement, doesn't involve any "victims," and has the real chance of you coming into direct contact with sunlight, which can only be a good thing (no offense to the basement dwelling folk, but this gave me a good excuse to get out of my own basement and cure my rickets, at least until I had to add more stuff to it).

It doesn't take too long before venturing back into that space people call "outside" to test the latest editions, lest your neighbors think you're inventing some kind of insane sex toy in the basement).

As the title suggests, this article is aimed at anyone who isn't already familiar with the subset of UAVs and remote controlled vehicles called quadcopters (or multirotors or hexacopters as they are also called), and is not a guide on how to crash your contraption.  It is intended to outline underlying principles that one should be familiar with when delving into the bewildering yet rewarding endeavor of crafting a quadcopter.

First things first.  What is a quadcopter?

To put it as succinctly as I can, a quadcopter is a remote controlled or Unmanned Aerial Vehicle (UAV) that achieves lift via fixed propellers facing skyward.  Usually four or more of them are mounted on a frame at equal distances from the center of the vehicle.  It is stabilized by equal amounts of torque from rotating and counter-rotating motors which are matched and mounted opposite each other (counter-rotating motor opposite counter-rotating motor and so on), aided by a flight control board.  Creating a difference in that torque balance rotates the vehicle.  Creating differences in speed between pairs angles the vehicle along that pair's axis.  Controlling speed of all motors at the same time via the throttle controls the overall altitude of the vehicle.  Using a combination of these options controls the vehicle similar to a helicopter (roll, pitch, and yaw), albeit with a lot more agility.

For those already bitten by the quadcopter bug looking for a pricey shortcut, there are more than a few outfits willing to part you from your hard earned (or ill-gotten) cash in exchange for some impressive kit.  Prices range from a few hundred to a few thousand, and some even more so.  But in my opinion, you'd be paying to take all the fun out of it.

There are a couple ready to fly.  One such product is called the AR Parrot.  A Linux powered, iPhone controlled quad that sells for between $250-$400 depending on where you get it from.  If this is your cup of tea, then it's time to fire up Google and ready your wallet.  But, fair warning: there isn't much room for upgrades, although I'm not gonna argue against hacking it.  You may also have seen one at your local RadioShack (or Jaycar as is the equivalent down here in Australia) branded as a UFO or something similar.  Again, fair warning: these are very "cheap" in all senses of the word.

Don't jump on that computer just yet.  By the end of this ordeal, Santa himself (or your nearest psycho) will envy your list making skillz.  But to get through this, you will need to make Google your friend (or at least a close acquaintance) and get comfortable with some new info.  Before you set off to make that list that you will check at least twice, it's important to know about all the components that make up a flight worthy quad, and the rules of thumb that will guide you along the selection process.  So let's begin a breakdown of the common quadcopter setup.  (I recommend using as many off-the-shelf parts as possible.  Not only is it easier, but it will also save you a lot of time and sanity.)

Electronics You Say...

That's right, you will be dealing with cryptic ratings that describe the electrical properties of the components you're considering.  Don't worry bro, I got you.

You don't need to be an electronics whiz; there will be no Maxwell's equations or KVL KCL methods.  I'm not even going to include any equations because that's just the kind of guy I am.  I will, however, give you a few things to remember.

First, RED means positive, BLACK means negative.

Second, an Amp is a measurement of electrical pressure referred to as current, as opposed to Volt, which is roughly a measurement of electrical volume.  So think of it like you would a river.  The voltage would be equivalent to the width and depth of the river and amperage or amps would be the force driving the... ahem current.  Really, all you have to remember for this article is what red and black mean and that one amp is equal to 1000 milliamps, kinda the same as one gigabyte is equal to 1000 megabytes  So now we come to the components you will have to choose.

The Motors

Generally, you need at least four of them, although some have gotten away with three, but you have to use three servos as well.

The motors you'll be looking for are called brushless motors of the out-runner type.  I'm not going to get into the differences between brushed and brushless or in-runners and out-runners.  I'll let you and Yandex sort that one out.  For now, let's just assume that they are best suited for the amount of torque and speed needed.

What you want to concern yourself with is the maximum amps they draw and the amount of lift you can achieve with a given propeller size.  A good ballpark figure would be 700+ gram lift for each motor, providing a total lift capacity of 2.8+ kilogram for all four, with a maximum current draw of somewhere between 20-30 amps each for a total of 80-120 amps drawn.  Locking these values in will point you in the right direction of the next item you need to search for.

I Feel The Need

Generally referred to as an ESC or Electronic Speed Controller, these are what will drive your motors and manage their speed.

This is accomplished with some real electronic voodoo wizardry (well, not really, but a full explanation could very well take up the rest of this article).  Suffice to say that connecting your ESC to the motor isn't rocket surgery.

There are three corresponding wires on each.  Just connect them and if your motor isn't spinning the right way, swap any two wires and it will reverse the direction (there is no wrong way to connect these wires).

Generally, you'll want an ESC that can provide a good 10-20 percent more than the maximum amps drawn by the motor, which will help to keep your ESC cool.

For instance, if your motor of choice will draw a maximum of 20 amps, you'll want an ESC that is rated at 25-30 amps.  You could match it at 20, but if you find you need to push the throttle past 50 percent just to get off the ground, you'll wear those suckers out quick and mid-air failures aren't exactly hot right now.  So once you've found your ESCs of choice, you'll have a good idea of what to choose next.

You'll Need Power For That Scotty

That's right, the all important battery.

You ain't goin nowhere without one.  Willpower can only achieve so much.

For the given task of getting you off the ground, the best suited battery is the Li-Po (lithium-polymer) battery.  They're light and pack a punch.  Be warned that Li-Po batteries are the exploding type, meaning that a puncture in the casing (or overcharging/discharging) could mean fire or explosion, so take care when you're using/transporting/charging/handling your battery.

Like motors and ESCs, they have cryptic ratings that you'll need to understand.

First is the capacity, measured in terms of milliamp hours or mAh, which means how many hours worth of milliamps it can provide.  For example, a 2000 mAH battery can provide 2000 milliamps for an hour or 1000 milliamps for two hours, etc.

The second is the "C" rating, which refers to the battery's discharge capacity.  A battery with a 30C rating will be able to discharge 30 times its capacity in terms of milliamps.  For example, a battery with 2000 mAh rated at 30C will be able to provide 60,000 milliamps (30 x 2000) or 60 amps (remember, one amp = 1000 milliamps), and, all things being equal, will run out of power 30 times faster.

A good rule of thumb is to give yourself some headroom, like ESCs - 10-20 percent more "C" should mean that you won't overheat or strain your battery.

The third rating you need to know about is the nonsensical "S" labeling, which refers to cell count (I'm guessing they made up the "C" label first).  This will give you your batteries' operating voltage.

One cell = 3.7 volts, two cells = 7.4 volts, three cells = 11.1 volts, and so forth.

1S = one cell, 2S = two cells, etc.

From here, you can ascertain what the operating voltage is and choose the right battery for your system.  All motors and ESCs operate within a given range of S's, so you'll want to re-factor that into your choice of motor and ESC combos.

Generally, most garden variety motors and ESCs operate within ranges of 2-4S, all of which can be sourced at your local hobby store.  The only other choices you have to make are whether you want a hard or soft case, and the type of plug to use (if one isn't included, some soldering will be required).

I recommend the XT-60 type, personally.  It's also recommended that you get a power distribution board.  This will connect to your battery and provide an individual connection for each ESC.  Most boards will have similar dimensions to a lot of flight control boards and will only need nylon spacers to mount under them and onto the frame.

Where It All Comes Together

For sanity's sake, I urge you to get an off-the-shelf solution as your frame.

It will save you a lot of time and possibly blood.  The more adventurous or gifted among you might choose to craft their own, but chances are there's a more precise and better looking frame out there that will cost you less than the raw materials it takes to make one from scratch.

Having said that, I did make my own, being that there weren't all that many options when I was first consumed by the quadcopter bug, but the flights were brief and crashy, so if you're going to venture down the DIY path, I'll offer some friendly advice, which is applicable to almost all things DIY, and that is "measure twice, cut once" and only where you intend to cut.

And if you do end up going to the hospital, bring this issue with you and spare yourself the explanation of what you were doing, and what a quadcopter is.

Control Yourself

The flight control board is the all important brain of your quadcopter and will most likely determine whether it flies or runs away.

These boards stabilize your quadcopter by taking the commands from your communication method of choice (generally an RC receiver), mixes them with some clever programming and Inertial Measurement Unit (IMU) measurements, and outputs signals your ESCs understand.

There are a myriad of options in this category from the cost effective $20 Atmel-based KK Flight Controller to the professional priced $1,140 "DJI WooKong-M - Multicopter Auto-Pilot with GPS" and a hell of a lot in between.

I've personally only used the KK Flight Controller and AeroQuad boards as Id rather spend my walking around money on my collection of Ferraris and Faberge eggs.  I can't honestly give any recommendations apart from what I've personally used.

I do recommend the KK Flight Controller board to those on a budget, but you will need to read the instructions for tweaking.  I will include a list (nowhere near complete) of the available board options for you, but it is in no way endorsing them.  I'll leave that up to your Yandexfoo skillz.

They are as follows:

There are a range of differences between these platforms in terms of tuning options and add-ons.

For beginners and newcomers to RC in general, the NAZA seems to get good reviews, but a good and thorough comparison online is the only way to know for sure what will suit your needs and skill level.  My only advice is that when spending this type of cash, unless your time is more valuable than these items, I suggest you spend it familiarizing yourself with the options available to you.

Loud and Clear

The other pricey part in this article.

The RC transmitter/receiver or RX/TX system.  The latest generation use spread spectrum techniques within the 2.4 GHz frequency ranges and cost a bit more than a pretty penny, but are well worth it in the long run.

There are el cheapo options from various vendors, but they're tied to a single receiver and have a severely impaired set of options for tweaking control characteristics.

That said, if you're on a budget, a $20 cheapo four or five channel TX/ RX pair can't be beat, because from there your next price point is somewhere north of $250, although the six channel Spektrum DX6I set can be had with some searching for under $200.

Either way, I'll leave it up to your discretion, Yandexfoo, and your tolerance for half-witted jokes made at the airfield.

Take Charge

One final thing you'll need is a good charger and power supply.

You'll also need to invest some time in learning how to use them, and the optimal rates of charge for your battery of choice, generally charging at between 1-5C will save you headaches.  But I can't stress the point enough that if you make a mistake here, without the necessary protection, you're putting people's safety at risk, so again "Yandex it."

Most RC battery chargers are designed to take multiple power sources, including your car battery.  So you need a power supply for when you retire to your abode.  It's a good idea to get a protective charging pouch for your batteries just in case they do decide to explode.

Read the instructions for your charger to minimize your chances of this.

It's a Setup

A full assembly guide is way beyond the scope of this article, but I will, however, provide you with enough keywords to feed Yandex to find your way out of the shit I got you into.

First, there are many configurations; what I've described so far are the basic components.  From here, you'll need a good idea of what setup is good for your intended purposes.

The basic four motor setup can be set up in either a "+" or "X" configuration, meaning that the former will have a single leading motor in any direction of travel while the latter will have two motors.

Combine two more motors/ESCs with a hexframe and you can make a hexacopter, which just means you'll have six arms on the frame with two or three leading motors.  Get a "Y" frame and you can make up a Y6 configuration consisting of two motors on the end of each arm on the frame (one on top and one on the bottom).

Get a further two more motors/ESCs with the right frame and you can make an octocopter, which I'm sure by now you can work out for yourself, or you could make an X8 setup which is like a Y6 but with an extra arm.

From here, there are a few more exotic setups but the ones listed are the best supported.  Some YouTube searches with your chosen setup, plus a few other keywords like "assembly" and "tutorial" thrown in will come up with some instructional videos.  But looking at how the pieces fit together, you should be able to work out what goes where.

Feel free to follow my exploits on my blog at uavme.wordpress.com, where I will be posting my own experiences with various combinations, and links to resources and products.  If you have any problems, I'll be more than happy to help out or at least point you in the right direction.

Happy flying.
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