Quadcopter using a Multiwii – Assembly

In the second part of this tutorial will proceed to the assembly of the Quadcopter .
If you want to see part 1, which are the various components shown , you can do it here.

Before beginning assembly it’s necessary to do the welding operations. If you have no experience in this area, ask for help to avoid accidents. It’s necessary to weld the bullets to the motor terminals and weld the XT60 plug to QBrain terminals. ATTENTION TO POLARITY. The red cable QBrain must match the red battery cable.

After the welds begins the frame assembly. For the frame in question, there is a manual that can be downloaded here. During assembly it’s necessary to perform an extra step to install QBrain. In step 8, before screwing the body, it is necessary to put between the plates, in the space formed by the arms, the QBrain. Prior to the screw, you must take note of all the information that is on the body.

Flightboard connections

The flightboard has several connectors. The following table precedes a brief explanation of each connector block :

Pins Description
I2C I2C connection. For a GPS.
UART Serial connection. Fro a bluetooth module to transmit telemetry
FDTI FDTI cable connection. Connects the flightboard  to the computer for configuration.
Pin with names -, + , D2,… Connections for the receiver
Pin with names 12, 8, 9, … Connections for the motors. The pins A0,A1 e A2 are used to conect a Gimbal servo.


Quadcopter using a Multiwii - Assembly

Connect the QBrain to the Flightboard

To connect the QBrain to the flighboard is necessary to identify, in the QBrain, which is the motor that can connect to each cable and, in the flighboard, which pin controls each motor. The first information is printed at the top of QBrain. The second can be found on the MultiWii site ( http://www.multiwii.com/connecting-elements ). Following this information the connections are:

QBrain Flighboard 
Motor 1 – Red cable Pin 11
Motor 2 – Orange cable Pin 9
Motor 3 – White cable Pin 10
Motor 4 – brown cable Pin 3

In the connections it is necessary to pay attention to the pin position on the flighboard. The outer row of pins is the negative pole, the middle one is positive and the inner is the control. In QBrain there are two cables for motors. One of the cables has a plug, and the other has three. The one who has only one plug transmits the signal to each engine. The one with three also powers the flightboard.

Connect the flightboard to the receiver

For connect the receiver to flightboard it’s necessary to identify each channel. In the case of this set – radio+ receiver – the channel’s are:

Channel Function
Channel 1  Roll
Channel 2  Pitch
Channel 3 Throttle
Channel 4  Yaw

In the flightboard cable is:

Pin Description
Powers theflightboard. Ground
+ Powers the flightboard. Positive
D2 Throttle
D4 Aileron ( Roll )
D5 Elevator ( Pitch )
D6 Rudder ( Yaw )
D7 Aux 1
D8 Aux 2 ( It’s necessary to define this pin on the Multiwii configuration )

These connections are made with the following cables:

Quadcopter using a Multiwii - Assembly

This flightboard allows to power the receiver. Therefore, we will use the cable that only has two plugs for the first connection. On one side we connect the receiver and the throttle connection; in the other connect,in the flightboard, pins ‘-’, ‘+’ and ‘D2’. It’s necessary to note what is the signal pin and what is the power pin, both at the receiver and flightboard.

Next connect the two cables having a plug at one side and three on the other. The side has only one plug connects to the flightboard and the three plugs connects to the receiver. The first cable connects to the pins ‘D4’, ‘D5’ , and ‘D6’ and the second in ‘D7’ and ‘D8’. In the receiver side the cables are connected according to previous table.

Calibrate propellers

Before we set up the blades it is necessary to calibrate them. The calibration consists in balance the propellers so as to have substantially the same weight on both sides. For this we can use a commercial equipment or build one of ours. In my case I print one, according to my needs. The template can be downloaded in my Thingiverse account ( find the link in the top menu ).

I use, for example, a screwdriver to support the propeller on the support and verify if it’s balanced. To do this check, put the propeller horizontally. If it remains in position, it is balanced . Otherwise, the descending side is heavier, therefore, need to proceed to a compensation. To do this, place small pieces of adhesive tape in the opposite paddle so we increase the weight. After each placement tape repeat the verification process till it’s balanced.

Quadcopter using a Multiwii - Assembly
Propeller calibrator
Quadcopter using a Multiwii - Assembly
Propeller calibrated

In  the third part we are going to configure the QBrain.

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