Initial Setup of a Multi-Rotor Aircraft – Ⅱ

Initial Setup of a Multi-Rotor Aircraft -Ⅱ

Assembling a multi-rotor drone

To assemble a multi-rotor drone, you must at least complete the following steps:

Load Firmware
Hardware Connection
Frame Setup
Radio Calibration
Compass Calibration
Accelerometer Calibration
Flight Mode Setup
Battery Monitor
ESC Calibration
Failsafe

Flashing ArduPilot Firmware

There are two methods for flashing firmware:

Online flashing: Connect to the Internet via the ground station to download and flash the firmware directly.

Local flashing: Load firmware downloaded from the website—or your own modified firmware—onto the flight controller via the ground station.

ArduPilot firmware is primarily categorized as follows:

Ground vehicles/boats: Rover

Fixed-wing aircraft/VTOL: Plane

Multirotors: Copter

Traditional helicopters: Heli

Underwater vehicles: Sub

Antenna tracker: Antenna Tracker

In-system programming

Connect the flight controller to your computer, open the ground station software, navigate to the “Initial Setup” screen, select “Install Firmware,” choose the desired firmware type, and wait for the flashing process to complete.

If the firmware version number is not displayed on the ground station, the issue may be due to a network problem or the ground station version itself. If online flashing fails, please select the option to load custom firmware (i.e., local flashing). If the progress bar below the firmware flashing status indicator remains stuck at “scanning COM ports” or “connecting” without advancing, please unplug and reconnect the flight controller.

Flash local firmware:

Please first download the firmware to your local machine or compile the firmware version corresponding to the hardware.

V5/V5+ Firmware (all official ArduPilot firmware): Multirotor (universal for 3–8 rotors)

Traditional Helicopter

Fixed-wing (including VTOL firmware)

Unmanned Ground Vehicle (UGV)

Unmanned Surface Vehicle (USV)

V5 nano Firmware (all official Ardupilot firmware):

Multirotor (universal for 3–8 rotors)

Traditional Helicopter

Fixed-wing (including VTOL firmware)

Unmanned Ground Vehicle (UGV)

Unmanned Surface Vehicle (USV)

Pixhack/v3/v3x/Pixhawk Multirotor (universal for 3–8 rotors)

Traditional Helicopter

Fixed-wing (including VTOL firmware)

Unmanned Ground Vehicle (UGV)

Unmanned Surface Vehicle (USV)

Hardware Connection

To help you complete the hardware connections more quickly, the simplest overall hardware framework for a quadcopter is described below.

Pixhack Series

Pixhawk

V5+/NANO

The image above shows a 4-in-1 ESC; typically, an ESC connects to a single motor.

Connect the motor to the ESC

Motor sequence for each type of aircraft (the numbers correspond to the flight controller’s PWM output ports).

The image above shows a 4-in-1 ESC; typically, an ESC connects to a single motor.

CW (clockwise rotation), green icon; CCW (counter-clockwise rotation), blue icon.

Incorrect hardware connections or the wrong firmware type can cause the craft to flip, spin, or fail to take off, or cause it to tilt severely to one side; please be sure to check for these issues.

Quadcopter

Tricopter

If the tricopter’s tail rotor responds in the wrong direction, the RC7_REV or MOT_YAW_SV_REV parameter should be set to -1 (changing it from 1); please refer to the Tricopter setup page for details.

Bicopter

Hexacopter

Y6

Octocopter

Octoquad

DodecaHexacopter

Identify clockwise and counter-clockwise propellers.

The image above shows two types of propellers: clockwise (known as “pusher”) and counter-clockwise (known as “puller”). As shown below, the correct propeller type is most reliably identified by its shape: when facing upward, the angled edge represents the leading edge in the direction of rotation.

Check motor rotation direction.

Once you have completed the ESC throttle range calibration, you can check whether the motor rotates in the correct direction:

Ensure the propellers are removed from the motors (testing motor rotation with propellers attached is strictly prohibited).
Turn on the remote control transmitter and set the flight mode to “Stabilize.”
Connect the battery.
Hold the throttle at the lowest position, and the rudder stick fully to the right for five seconds to arm the system.
If the system fails to arm and the motors do not spin, the remote control may be uncalibrated or a safety check may have failed; connect to a ground station to view the error messages.
After arming, apply a small amount of throttle and observe/record the rotation direction of each motor. They should match the directions shown in the diagram for your chosen frame configuration.
Reverse the direction of any motors rotating incorrectly (for standard motors and ESCs, this is typically done by swapping the connection of any two of the three wires connecting the ESC to the motor).

Use the Mission Planner motor test to check motor numbers.

Another way to verify that the motors are connected correctly is to use the “Motor” test in the “Mission Planner Initial Setup” menu.

After connecting the flight controller to the ground station, you can click the green button displayed above, and the corresponding motor should spin for five seconds. The letters correspond to the motor numbers, as shown in the example below.

First, remove the propellers!
If the motor does not spin, increase the “throttle” to 10% for a longer duration and try again. If that does not work, try 15%.
On a “+” configuration frame, the first motor to spin is located directly at the front; on an “X” configuration frame, the first motor to spin is at the front-right. The motor test sequence then proceeds clockwise.
On an X8 frame, the top-right motor spins first, followed by the bottom-right motor, continuing in the same pattern.
On an OctoV frame, the front-right motor spins first, followed by a clockwise sequence until the front-left motor is reached.

Rack Type Configuration

Under Initial Setup – Required Hardware – Frame Type

Configuration methods:

Method 1: Connect the flight controller to the ground station, then navigate to **Initial Setup** > **Mandatory Hardware** > **Frame Type** and select the appropriate frame class and frame type.

Method 2: Locate the **FRAME_CLASS** and **FRAME_TYPE** parameters in the **Full Parameter List** and modify them to the appropriate settings based on the descriptions provided in the comments.

Note: For firmware version AC3.5 or later, configuring the frame type is mandatory; otherwise, a “check frame_class or frame_type” error will occur.

RC Remote Controller Calibration

Overview:

This article explains how to calibrate your radio controller using Mission Planner.

The remote controller allows the pilot to set flight modes, control the drone’s movement and orientation, and toggle auxiliary functions (such as raising and lowering the landing gear).

Calibrating the remote controller involves capturing the minimum, maximum, and midpoint values for each RC input channel so that ArduPilot can correctly respond to your inputs.

Channel Usage

A multi-rotor requires a minimum of five control channels (default: 1-Roll, 2-Pitch, 3-Throttle, 4-Yaw, 5-Mode Switching).

Any unused channels can be connected to external devices or left idle.

Check the remote control signal

Ensure the battery is disconnected (this is important, as the motor could accidentally spin up if the throttle is triggered during calibration).
Ensure the RC receiver is connected to the autopilot.
Turn on your RC transmitter; if the sticks are self-centering, ensure they are in the neutral position.
Connect the autopilot to your PC using a USB cable.
In Mission Planner, click the “Connect” button, then navigate to the **Initial Setup > Mandatory Hardware > Radio Calibration** screen.
You should see green bars indicating that ArduPilot is receiving input from the transmitter/receiver. If no bars appear, check the connection between the flight controller and the receiver, as well as the link between the transmitter and the receiver.

If the indicator light on the remote control receiver does not light up, try inserting the connector the other way around; if your remote control and receiver have not been paired, you need to consult the remote control manual to perform the pairing process.

Check the channel mapping in your transmitter by moving the sticks, knobs, and switches and observing the movement of the green bars (if present)—that is, verify which input channels correspond to which transmitter controls.
Determine whether your transmitter is Mode 1 or Mode 2 (see below)
The Roll stick should control Channel 1
The Pitch stick should control Channel 2
The Throttle stick should control Channel 3
The Yaw stick should control Channel 4
A three-position switch (for flight modes) should be set to control Channel 5 (default); you can also change the control channel for flight modes by adjusting the `FLTMODE_CH` or `MODE_CH` parameter.
If a green bar moves in the wrong direction, reverse the channel on the transmitter itself; if the channel cannot be reversed on the transmitter, you can reverse it by directly changing the `RCx_REVERSED` parameter (where “x” is the input channel number, 1 through 4).

Perform calibration:

Click “Radio Calibration.”
Select “OK” in the pop-up dialog box.
Move the transmitter’s sticks, knobs, and switches to their extreme positions. Red lines will appear on the calibration bars to indicate the minimum and maximum values recorded so far.
Click once you have finished making the selections.
A window will appear prompting you to “Ensure all sticks are centered, throttle is down, and click OK to continue.” Set the throttle to zero and press “OK.”
Mission Planner will display a summary of the calibration data. Typical values range from approximately 1100 (minimum) to 1900 (maximum).

The standard values range from 1100 to 1900; ensure they are neither too low nor too high—especially for the throttle channel—to avoid anomalies.

Remote control type:

There are generally three common control modes for remote controllers:

Mode 1 (Japanese Mode): The left stick controls pitch and yaw, while the right stick controls throttle and roll.
Mode 2 (American Mode): The left stick controls throttle and yaw, while the right stick controls pitch and roll.
Mode 3 (Chinese Mode): The left stick controls pitch and roll, while the right stick controls throttle and yaw.

Each mode has its own advantages and depends on personal preference; there is no single “best” mode, only the one that suits you best.

MODEL 1 (Japanese-style transmitter) – Schematic diagram

Model 2 (US-style) – Schematic Diagram

You can set the remote control type using your remote control.

Compass Calibration

This section explains how to perform a basic compass calibration.

This assumes you are using the most common configuration—with the autopilot and compass oriented so that their arrows point toward the nose of the drone. If you are using a different configuration, please refer to “Advanced Compass Settings.”

Calibration process

Do not calibrate the compass near objects that generate metal or magnetic fields (such as computers, mobile phones, metal tables, or power supplies), as this may result in calibration errors.

Open Ground Station Initial Setup > Mandatory Hardware > Compass Calibration.

Generally, you do not need to change any “General Compass Settings” or compass-specific values (i.e., the “Compass #1” section), but you should verify that the “Enable compass and auto-detect magnetic declination” box is checked. If you frequently see “Compass Inconsistent” warning messages and are certain that the external compass is oriented correctly, you can disable Compass #2 (the internal compass).

Click the “Start” button.

If your autopilot is equipped with a buzzer, you should hear a prompt tone followed by a short beep every second.
Pick up the drone and rotate it in various directions, pointing each side (front, back, left, right, top, and bottom) toward the ground for a few seconds.

As the drone rotates, the green indicator bar should extend further to the right until calibration is complete.
Upon successful completion, three beeps will sound, and a “Please restart the autopilot” window will appear. Switch to another screen and then back to this one to view the resulting offset values; a green value indicates a good result (absolute value of each offset < 400), yellow indicates an acceptable result (absolute value of each offset < 600), and red (provided the value is non-zero) indicates a potential issue (such as magnetic field interference).

After calibration is complete, you need to restart the autopilot.

If calibration fails: You will hear an error tone, the green progress bar may reset to the left, and the calibration routine might restart (depending on the ground station). If the compass cannot be calibrated after multiple attempts, press the “Cancel” button, change the “Fitness” dropdown menu to a more lenient setting, and try again. If compass calibration continues to fail, you can identify the problematic compass—which may be experiencing magnetic interference—via the “Flight Data” > Status interface. Calibration failures are typically caused by magnetic interference affecting one or more compasses; you can diagnose this by analyzing the compass (mag) data shown in the image above. Under normal conditions—and prior to successful calibration—the X, Y, and Z values should not exceed 700 (regardless of sign), and fluctuations should remain within a range of 20. Failure to meet these criteria indicates the presence of continuous or intermittent magnetic interference; you can resolve this by adjusting the compass’s mounting position or removing the source of the interference.

Trigger on-board calibration using the remote controller (without GCS)

Copter-3.4, Plane 3.4.0, and Rover 3.0.0 (and later) firmware support triggering onboard calibration via the RC transmitter, allowing for compass calibration without a ground station.

Ensure that RC calibration has been completed.
Move the throttle stick to the maximum position while holding the yaw (rudder) stick fully to the right; hold this position for 2 seconds (do not disarm the safety switch during this process).
If your autopilot is equipped with a buzzer, you should hear an initial tone followed by a short beep every second.
Pick up the vehicle and rotate it in various directions so that each side (front, back, left, right, top, and bottom) points toward the ground for a few seconds.

Upon successful completion, three beeps will sound, and you will need to restart the autopilot.

RC Remote Controller Calibration

This section describes how to perform basic accelerometer calibration (using Mission Planner).

Accelerometer calibration is required in ArduPilot.

3D Accelerometer Calibration

If the flight controller is mounted in a non-standard orientation (i.e., the arrow does not point forward), ensure that AHRS_ORIENTATION is correctly configured before performing accelerometer calibration.

In Ground Station > Initial Setup > Mandatory Hardware > Accelerometer Calibration

The green box indicated by the upper arrow is for 6-axis (3D) accelerometer calibration, while the green box indicated by the lower arrow is for accelerometer neutral/level calibration; firmware versions AC3.4.0 and later require both 3D calibration and level calibration.

Click “Calibrate Accelerometer” to begin calibration. Mission Planner will prompt you to place the drone level; once positioned, click the designated button to confirm, then follow the prompts to calibrate the remaining orientations.

The calibration positions are: level, right side, left side, nose-down, nose-up, and upside-down.

Importantly, the drone must remain completely stationary immediately after pressing the button at each step. If the drone is too large to position conveniently, you can perform the calibration before assembly. A correct horizontal position is crucial, as it serves as the level reference for the drone during flight; therefore, horizontal calibration is essential.

After completing the calibration process, Mission Planner will display “Calibration Successful!”, as shown below.

Level calibration

Firmware versions AC3.4.0 and later require both 3D calibration and level calibration to ensure the accuracy of the horizontal reference during flight.

After calibrating the accelerometer, click the “Calibrate LEVEL” button; the flight controller will enter initialization mode (LED flashing rapidly). When the button changes to “Completed,” the level calibration is finished.

After calibrating the accelerometer and compass, it is recommended to power-cycle the device; otherwise, abnormal error messages may occur.

Airplane mode settings

Flight modes are configured via the remote control receiver; by default, up to six flight modes can be set.

For beginners, using three modes is sufficient; otherwise, confusion when switching between them could lead to a crash.

Setup steps:

Connect to the ground station via USB or a data link.

Go to Initial Setup > Mandatory Hardware > Flight Modes

Toggle the multi-position switch assigned to Channel 5 on your remote controller (Channel 5 is the default control channel for flight modes on multi-rotor aircraft). Observe the mode corresponding to each switch position, select the desired flight mode for that position from the drop-down menu, and then click “Save Mode.”

For beginners, it is recommended to use Altitude Hold, Loiter, and RTL (Return to Launch) modes; for newly assembled aircraft, the recommended configuration is Stabilize, Loiter, and RTL modes.

If the mode doesn’t change, check whether the current PWM value is actually changing or if the change is too small.
Each mode operates within a specific PWM range; the mode will not switch if the signal stays outside these thresholds. You may need to adjust your remote controller’s settings. There are 14 modes in total; please refer to the next section, “Flight Mode Introduction,” to understand the meaning and function of each one. A standard three-position switch can only toggle between three modes (yielding only three PWM values), but you can use mixing functions to access six modes.

Battery Monitor

This section explains how to set up a battery monitor (using Mission Planner). The battery monitor—also known as a power monitoring module—transmits real-time battery current and voltage data to the flight controller; the drone uses this data to determine whether a “Return to Launch” (RTL) is necessary, thereby preventing a crash caused by a loss of power.

Overview:

CUAV has designed three different power monitoring modules to meet diverse user needs:

CAN PMU: Digital, ultra-high-precision power monitoring module
HV PM: High-voltage, high-precision power monitoring module
CPBD: Power distribution board
PM Power Module: Standard power module

Please click here for more information and settings regarding the power module.

ESC (Electronic Speed Controller) Calibration

The Electronic Speed Controller (ESC) is responsible for driving the motor at the rotational speed requested by the flight controller. Most ESCs require calibration so they can recognize the minimum and maximum PWM values sent by the flight controller. This page provides instructions for calibrating ESCs.

Regarding ESC calibration:

Calibration procedures may vary depending on the specific Electronic Speed Controller (ESC); please consult the manual for details, as the audible tones or signaling methods might differ, though the general process is usually quite similar.

Most ESCs can be calibrated using a unified method (calibrating via the flight controller after the aircraft is assembled). If unified calibration has issues—such as a lack of synchronization—you can opt for individual calibration (calibrating each ESC one by one using the remote control receiver).

Uniform calibration of all ESCs:

Pre-calibration checks:

Ensure the ESCs are installed and the signal cables are properly connected to the flight controller.
You must remove the propellers before calibration!
Do not connect to a computer via USB.
Verify that the stick channels are not reversed before calibrating.

Calibration steps:

1. Turn on the remote controller and push the throttle to the maximum position.
2. Connect the battery to the aircraft and disengage the safety switch; the PIX status LED should now cycle through red, blue, and yellow flashes, indicating entry into the ESC calibration mode.

3. Disconnect the battery and then reconnect it; the tricolor light will continue to flash. Immediately press and hold the safety switch to unlock the system; release the switch after a few seconds, once the light remains solid.

4. Wait for your ESC to emit a series of tones. The initial beeps indicate the battery cell count (e.g., three beeps for 3S, four beeps for 4S), followed by two beeps indicating that the maximum throttle position has been recognized.

5. Move the transmitter throttle stick to the lowest position; the motor should emit a long tone, indicating that the minimum throttle position has also been recognized and recorded.

6. Next, advance the throttle to verify that all motors spin up correctly and synchronously; if they do, the calibration is complete.

7. Keep the throttle at the lowest position and disconnect the battery to finish the calibration process.

Individual ESC Calibration

Plug the ESC signal wire into Channel 3 (the throttle channel) of the receiver.
Turn on the remote controller and set the throttle stick to the maximum position.
Connect the battery to the ESC to power it up.
The motor will emit a specific tone, followed by two beeps (refer to the ESC manual for the exact tone).
After the two beeps, move the throttle stick to the lowest position.
You will hear a series of beeps (e.g., three beeps for a 3S battery), followed by a long beep confirming that the throttle has been calibrated.
Gently push the throttle stick to check if the motor spins in response.
If the calibration is successful, repeat the same procedure for all other ESCs.

The above covers the assembly and initial setup of a multi-rotor aircraft. Due to the extensive nature of the topic, this guide focuses solely on firmware loading and hardware connections; details regarding failsafe mechanisms will be covered separately.
Stay tuned for the next installment:
《Multi-Rotor Aircraft Initial Setup – Part II (Failsafe Mechanisms)》

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