Quad Build Part 3

Before I begin, an apology. I think anyone who starts their own website, blog, etc. does so with the best of intentions to post regularly. I admit to being slightly remiss in that respect; forgive me readers for I have sinned … it has been 34 days since my last quadcopter post …

So that out of the way, where were we? In the last part the rotor arms had been fastened to the bottom chassis plate and the motor power leads & main battery connector soldered to the plate. Time to introduce you then to the FC … or Flight Controller. This is the brain of the quad and even the cheapest FCs offer pretty remarkable features and processing ability. For anyone who fancies digging a little deeper, I recommend this page on Oscar Liang’s excellent website.

Below is the FC I purchased for my build, mainly because it was the closest I could get to the one used in the HackSpace article. It’s not the smallest or the most powerful but it’s pretty cheap and has all you’ll need for a beginner’s craft. The mounting centres are at 31.5mm so that should give you an idea of its overall dimensions.

Flight controller top side.
Flight controller top side.
Flight controller underside.
Flight controller underside.

Here it is installed onto the bottom chassis plate with 3mm nylon stand-offs and rubber grommets in the mounting holes to help absorb some of that ever present vibration.

Flight controller in situ
Flight controller in situ

Time for a brief aside me thinks … please feel free to skip if you like! The observant amongst you will have noticed the ARM logo on one of those chips above and ARM has a history that started when I was first getting into computers at school. For those in the UK of my age group, cast your mind back to the early 80’s when the BBC embarked on a mission to get the nation computer literate and commissioned the BBC Micro which was made by a British company called Acorn Computers. Founded in 1978, Acorn developed a RISC (reduced instruction set computer) processor and the company eventually became ARM Holdings whose ARM architectures can be found in smart phones, digital TVs, set top boxes, mobile computers and, of course, flight controllers! From the Wikipedia entry above: In 2013, 10 billion were produced and “ARM-based chips are found in nearly 60 percent of the world’s mobile devices” … that’s a pretty impressive track record in anyone’s books.

To those who read my little aside, thank you very much. And those who skipped it, hey I won’t hold it against you. Back to the build and the first wiring to connect to the FC was the main power feed, which you can see is picked up from the internal PCB tracks of the chassis plate making routing cables much easier and neater.

FC with power connections
Power feed to FC.

Then came the tricky part of connecting the control wires from the motor ESCs. Two problems here; the solder pad on the FC for the control wire is roughly 1.5mm diameter if you’re lucky & close to the FC mounting holes (necessitating removal of the nylon screw nearest the pad so as not to melt it with the soldering iron) and space is limited for access. There’s also the age old problem of not having a 3rd hand to hold the wire in place whilst holding the soldering iron with the 1st and applying solder with the 2nd! When I was researching connections for the ESCs I saw a post where the constructor had coiled the wires to allow some resilience to vibration, which I thought a good idea. It also looks pretty trick, to coin a ‘yoof’ phrase!

ESC control wire connection
The first ESC control wire connected … for motor 1.
All ESC control wires connected
All ESC control wires connected to the FC.

And that’s it for Part 3. The next & final build post will look at the radio control receiver, finishing off the build & a little setup I knocked together to calibrate level for the gyroscope on the FC.

Quad Build Part 1

As I mentioned in a previous post, the core parts used for building a basic quad(copter) are minimal and pretty easy to assemble. Unfortunately, those parts tend to ship with little, or nothing, in the way of instructions … which is of particular importance when it comes to the electrics and electronics. As anyone knows, when the magic smoke escapes from a component it’ll never work again! Luckily for all concerned, the web holds a plethora of information from those who have been here before.

So to step one; basically a quad has a central platform to hold the FC (Flight Controller), battery and receiver for the radio control system. From this centre extend four rotor arms to which are affixed the motors (complete with corresponding rotor blades) and each motor’s ESC (Electronic Speed Controller).

First the motors are fixed onto the arms:

Fastening a motor to a rotor arm

Motor in situ showing power leads

So far so easy. The ESC’s have three solder pads to connect the three wires from the motor to, but nowhere does it say which wire goes to which pad!

ESC connections as supplied

Motor to ESC wiring

It turns out you can connect the wires in any order you like … honestly. The only criteria being that you need to wire all the motors the same to get them to spin in the same direction and (something that will be explained later, and which is important to drone flight) swapping over the two outer wires will make the motor spin in the opposite direction. Who’d have thunk it?    So to the other end of the ESC. There are two heavy wires (black & red) which are the power feed from the battery. The other pair take the signal from the FC and control how fast the motor spins. One of this pair (the brown) goes to ground and, as the black power cable already gives a ground connection, can be removed. That leaves a single orange wire which is soldered directly to the FC. The flight controller I purchased has no plug & socket connectors for the various components so they all have to be soldered into place.

ESC with modified wiring

Time for a brief science interlude! Most people know the theory behind how a helicopter flies: the main rotor blades spin and force air downwards, this in turn causes lift which allows the helicopter to leave the ground. As the rotor spins, the body of the helicopter has the tendency to want to rotate in the opposite direction … not a problem when on the ground as the friction between the skids, or wheels, and the ground stop the body from rotating. Once off the ground, without a tail rotor the helicopter would be totally unstable and uncontrollable. The tail rotor spins and creates a flow of air sideways to balance the helicopter body’s desire to rotate. Now consider twin rotor helicopters like the Chinook. These have no tail rotor but keep the body stable by having one main rotor spinning clockwise and the other spinning anti-clockwise … the overall effect being to create lift without the helicopter body spinning out of control. Multiply this by two and you have the quadcopter. In this case, to keep the rotational forces in balance, two rotors spin clockwise and two spin anti-clockwise. Generally this is configured as in the diagram below with the arrow being the direction of forward flight:

So, adding the last piece of information to what I learned earlier about swapping the outer wires on the ESC … motors 1 & 4 are wired one way and motors 2 & 3 have the outer wires swapped over … simples! I later found out that you can wire all the motors the same and then program the ESC’s to rotate the motor whichever way you see fit. I preferred to have the motors rotating correctly without any fudging via software so I made sure the wiring was completed correctly in the first place.

Step one was to feed the motor wires through the rotor arm, slide some heat shrink tubing over the ends then solder the wires to the ESC.

Then the heat shrink was slid over the soldered joints and shrunk into place using a hot air gun.

Finally a small pad of self adhesive foam was stuck to the back of the ESC and it was loosely cable tied to the rotor arm to allow some resilience to the inevitable vibration that a spinning rotor causes. The power and control wires were fed along the arm ready to be attached to the FC.

Et voila, all four rotor arms ready to be attached to the main central chassis and four motor/ESC combinations ready to be connected to the FC.

So it begins …

Before I start I think I’d better clarify a few points:

  • A quadcopter is a drone but a drone is not necessarily a quadcopter … much like a Hoover is a vacuum cleaner but not all vacuum cleaners are Hoovers!
  • According to the Cambridge dictionary a drone is “an aircraft without a pilot that is controlled by someone on the ground”. Unfortunately a lot of people see a drone as synonymous with an aircraft used for dropping bombs or for covert surveillance . However, a lot of people get fun (and enjoy the challenge of) racing drones, some people just enjoy flying them and I’m sure everyone has seen some of the stunning aerial footage that has begun to appear in films (without the use of CGI) and TV programmes courtesy of drones.
  • A quadcopter has four rotor blades (quad meaning four). Hexa (6) & Octo (8) ‘copters are also available, should you so desire.

S0 that out of the way, why build a quadcopter? Well, I’ve had a bit of a fascination for quadcopters for some time but they seemed to fall into two categories … toys or ridiculously expensive machines used by ‘professionals’. That was until I received issue 10 of HackSpace magazine and saw the image on the front cover …

… there’s that word again … drone!

I read the article and realised that it wasn’t as expensive or as complicated (Yeah right!  The basics are straight forward but dig a little deeper and you discover a world of acronyms and technology … right up my street then I guess) as I’d first thought and, to cut a long story short, I bit the bullet and ordered a bucket full of goodies online ready to start my new adventure ….