Quad Build Part 2

This post is quite a short one, covering the basics of the PCB (printed circuit board) based chassis plates and connecting the rotor arms to create the quadcopter’s familiar configuration.

The top and bottom members that hold the rotor arms in situ are multi-layer PCBs. This gives a combination of strength from their fibre glass construction and flexibility of electrical connectivity from the copper tracks that run between the fibre glass layers & their break out points on the chassis faces.

The main battery connector is attached to the bottom chassis plate as  shown below with the black wire soldered to the -ve pad and the red wire to the +ve pad (pretty basic stuff so far!). The beauty of the PCB chassis is that all the pads marked + are connected together, likewise those marked   . This makes connecting the main power feeds to the ESCs very simple as can be seen a little later on.

Main battery connection

As the battery connector will be routed towards the top chassis plate (when fitted) I thought it wise to add some strain relief on the soldered joints by applying a little hot melt glue.

Glue added as strain relief.

The assembled rotor arms from Part 1 are attached to the bottom plate using cap head bolts provided with the air frame kit (2 per arm) and the 2 ESC power feed wires soldered to the relevant pads on the PCB (as mentioned earlier). This leaves the orange control wire to the ESCs ready to be soldered to the FC later on. You’ll also notice I’ve numbered each arm to correspond with the diagram in Part 1 so I mount them in the correct location and use the correct rotor blade for each motor.

Rotor arms mounted to chassis.
Numbered rotor arms
ESC connections to bottom plate & orange speed control wires.

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.