Quadcopter Build 4: Connecting it all up


Last month we looked at how the power systems worked on a multirotor and explored why we needed to have both a main battery connection for the motors but also a 5v system to power the flight controller and radio receiver too.

By now the model should be starting to look like a quadcopter and we can finally start to connect everything together and also setup the radio so that it will work when we finally configure and test the model next month.

So, let’s look at the how we connect the main pieces first.

The PDB, the ESCs and the motors

As we looked at last month, the PDB connects all of the power wires from the ESCs together so that all of the ESCs can draw on the power of the main flight battery to turn the motors.
The first thing we need to do is make sure that none of the exposed contacts on the PDB touch the frame or any other conductive surface. Don’t use metal screws to mount anything and its normal to mount the PDB with the flight controller on top, again making sure that none of the contacts touch anything they shouldn’t! Many pilots use nylon washers underneath and I also cover the bottom of the PDB with insulation tape to be doubly safe. But until we’ve soldered a few things more then we can’t use the tape.

If the PDB you have doesn’t already have a battery connector attached then that’s the first job. Make sure you’re using a good quality soldering iron, top and lead based solder to get a great joint. Once that’s done then place the board where it will be finally installed and clip the wires from the ESCs to the right length so they will reach the pads on each side/corner of the PDB. Double check that all of the red wires are going the pads marked ‘+’ and the black wires to those marked ‘-‘. Always err on the side of caution and leave an extra 5mm more than you think you need. Strip the ends of the wires and carefully solder each ESC to the PDB (see why we’ve made the glossary now?)

The last step is to solder any extra wires to the PDB that you’ll need in future. If you are using OPTO speed controllers then you’ll need to connect the 5v out from the PDB to the flight controller to power it and I also connect a ‘spare’ JST connector to the 12v/battery pads too as it comes in handy later if you want to add LEDs or FPV equipment to the model. To power the flight controller I use a servo style lead from the 5v and plug it into a spare motor output on the flight controller to power everything.

With all of that done then it’s time to connect the motors to the ESCs. Few motors and ESCs now come with connectors so you’ll need the soldering iron again. Solder the three wires from the ESC to the three wires on the motor. Don’t worry about connecting them the wrong way – you can’t. If the motor turns the wrong way when we test it then you simply swap any two of the three wires to make it turn the other way. Cover the temporary solder connections with tape to stop them touching each other – this will damage the ESC if it happens.

Connecting the signal wires

Now the PDB, battery connector, ESCs and motors are connected then the soldering should be done (for now!).

There are the signal wires out of the flight controller to send the signals to the ESCs on how much power is needed for each motor. There are also signal wires from the radio receiver to send the signals from the radio to tell the flight controller how you want the model to move.

layout.pngConnecting the ESC cables

Every flight controller and its software has its own convention when numbering the motors. The most popular flight controller software – Betaflight, Cleanflight and Baseflight – all share a common motor layout.

If you place the model on the table in front of you with the nose pointing away then the front left motor is number 4, the rear left motor is number 3 and so on. One of the common mistakes for new builders (and some not so new builders) is to plug the motors into the wrong outputs on the flight controller. Our top tip is marking the servo connectors that relate to each motor with that motors number. It will avoid that common mistake of plugging them into the wrong output if you do.

Now it’s a simple case of plugging the right numbered motor connection into the right numbered output on the flight controller. Make sure that the black wire on the connector is plugging into the ground pin, this is normally marked on the board.

If you’re not using Cleanflight or similar then check what the motor connection numbers are. For example LibrePilot (usually used with CC3D flight controller) has a completely different numbering scheme. Connecting the motors up the wrong way will cause the model to dramatically flip on take-off so double check!

Connecting the Radio Receiver signal wires

The three most common ways to connect a radio receiver to a flight controller:

PWM (Pulse Width Modulation)

  • Uses a separate cable for each of the 5 channels we need to fly.
  • Advantage – very fast,
  • Disadvantage – lots and lots of cables to manage and get plugged in the right order at each end.

S-BUS (Serial BUS)

  • A very fast digital connection that uses only one wire to send all of the signals to the flight controller.
  • Advantage –Very fast and only one wire so easy to wire up,
  • Disadvantage – Some flight controllers can’t support the inverted signals that this method uses without extra circuitry.

PPM (Pulse Positon Modulation)

  • An analogue system that uses one wire to send up to 8 channels.receiver-connection.jpg
  • Advantage – widely supported and easy to setup,
  • Disadvantage – not quite as fast as S-Bus
If you have a radio receiver that has a PPM out and a flight controller with PPM in then, for a new builder, I’d go for a PPM connection every time.

If you do have PPM when connect the single three wire cable from the flight controller to the radio receiver. The white/yellow wire will send the PPM signals the flight controller needs and the black and read/Brown and orange wires will power the radio receiver using the 5v supply plugged into the flight controller.

Setting up the model on the radio.

Now we’ve got all of the power and signal cables connected we need to setup a new model on the radio that we can use to fly with. You’ll need a fresh memory on the radio you are
using and setup the radio to have the following controls –


Aileron (also referred to as Roll)

This control makes the model roll from side to side. On a multicopter facing away from you it makes the model move right and left.

Elevator (also called Pitch)

This control makes the model roll from front to back. On a multicopter facing away from you it makes the model move forwards and backwards.

Throttle (sometimes called Power or Engine)

This control makes the model rise and fall.

Rudder (also called Yaw)

This control makes the model rotate. On a multicopter facing away from you it makes the model rotate left and right about its axis.

Mode (commonly called Aux1 on a radio)

This channel is needed to tell the flight controller how to fly and what mode to use. You can have many modes setup but most pilots setup a three position switch for this and that allows up to three flight modes to be selected easily.
In addition to these basic 5 channels/controls many pilots will add others controlled by switches too to operate lights and buzzers and other functions on the model.
In addition to these basic channels I’d also look at setting up the following on the radio ready for flying and the next steps –

Add a timer

When you start to fly its common to get caught up in the flight and forget how long you’ve been flying. Setup a timer so you can have it keep track of your flight time so you never over-discharge the battery

Arming control

Consider setting up another switch to use to ARM the craft. Next month we’ll look at this and you can arm a model without a switch being assigned. Most flight controller like to use the throttle and rudder to arm but many pilots like a ‘safe’ setting on the radio.

Endpoints and sub-trim adjustment

Have a look and make sure you know where these are in the menus on the radio. Endpoints are used to make sure that the throttle, aileron, elevator and rudder don’t send too high, or too, low for the flight controller. The sub-trim is used so that the controls send the perfect ‘middle position’ the flight controller too so that the model doesn’t think you want to move when you don’t. This is one of the most common causes of models ‘drifting’ when flying.

Make sure your ‘failsafe’ setting is enabled.

Failsafe is what happens if the radio receiver in the model loses connection to the radio. I’ve had lots of subscribers who have lost a model because this wasn’t setup. The most dangerous setting is usually called something like HOLD on the radio and this tells the receiver to send the last control positions it hears, and keep doing so, if it loses connection to the radio. Imagine what that means if you were flying away from yourself and climbing. If there is a problem the model will continue to do that until the battery runs out! Normal failsafe settings are all controls at neutral with the throttle at the low position. Don’t fly unless you’ve tested your failsafe.

Bind the radio receiver to the radio

We will end up doing this one last time next month once we are happy everything is setup perfectly but binding now makes sure we can come back next month and run through the setup on the model to test everything and fine tune the setup.


So now all those spate pieces you started out with are now all connected together and starting to look a lot like a multirotor! Next month we’ll look at the steps with the flight controller to make sure that the radio and motor setups are ok, setup the first flight modes, calibrate the ESCs and check the failsafe before adding the props and trying the first test hover!
Join us next month for the final steps to get in the air!
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