APM Overview

APM 2.5

The APM 2.5 board requires no assembly, and is ready for firmware. You have a choice of side 

or top entry pin configuration, in order to accommodate a variety of installations. You’ll see this 

option when you order.

***Click and drag the image above to spin it!

This page gives you a look under the hood, and goes into more detail about the design of this 

board.

The APM 2.5 has some improvements over the APM 2.0, but they both have a very similar 

layout and function.

APM 2.6

 APM 2.6 is a revision of the APM that makes use of an external magnetometer 

(compass).

 The APM 2.6 has no on board compass, and is optimized for vehicles where the compass 

should be placed as far from power and motor sources as possible to avoid magnetic 

interference.

 APM 2.6 is designed to be used with the 3DR GPS uBlox LEA-6 with Compass module.

 The GPS/Compass module may be mounted further from noise sources than the APM 

itself.

 APM 2.6 requires a GPS unit with an on board compass for full autonomy.

 For information on installing a 3DR GPS uBlox LEA-6 with Compass, visit .
Using the APM 2.5/2.6 Enclosure

The APM 2.5/2.6 board is shipped in an enclosure with foam protecting the barometric pressure 

sensor, as shown here.
Or Not

If you aren’t using the enclosure, make sure to cover the barometric sensor with some open cell 

foam, cotton padding or tissue to protect it from prop wash, wind and turbulence. Also, the 

barometric sensor is sensitive to light and readings can change by several meters from direct 

sunlight to shade. Some type of light shield (on top of the foam) will minimize the effects of 

light changes.
Powering the APM 2.5/2.6 Board

Like any computer, the APM needs a power supply with a steady clean voltage and sufficient 

current.

3DR provides an APM power module that supplies 2.25A at 5.37V. The module is designed to 

convert power from the main flight battery (18 volt maximum). That module will supply

sufficient power for your APM, and low power radios including your RC receiver (without 

servos). Your RC receiver can be powered from any APM Input (+5V and ground). This is 

normally done by connecting a 2 or 3 wire cable between an APM Input and one of the output 

channels on the RC radio.
If you are using any servos such as are required with a traditional helicopter or a camera gimbal, 

you will need to provide an additional dedicated power supply for the servos. The APM is 

intended to control servos, not power them.

In order to design a power supply for your APM, or provide additional power, you’ll need a 

basic understanding of the power circuit in the APM.

There are two “sides” to the positive circuit in the board. Each side has positive-rails available 

for inputing power or distributing it to peripheral devices. The center row of pins in the three 

groups of pins (Outputs, Inputs, Analog) labeled “+” are referred to as a “positive-rail”. This 

means that the base of all the + pins are connected so they represent a single electrical path. The 

positive-rails of the Input and Analog group are connected together. So we have two separate 

positive circuits, one in the Outputs and the other made up of the Input/Analog.

All of the components on the board take power from various points on these rails, so it is 

necessary for both “sides” to be receiving +5V (within the specs below) for the board to 

function.

These positive-rails can be joined together by placing JP1 in it’s position on the board. This 

connects all the positive-rails ands provides power to both sides of the board, so that low-level 

power can be distributed to peripheral sensors and devices: 3DR Radios, sonar, RC Rx, etc. via 

the power-rails.

When using the power module, the circuit path is as follows:
From the power module connection the negative wire is connected to a negative-rail shared by 

the entire board regardless of JP1.

Positive voltage comes in to a T-junction. to the left is a path through the JP1 to the positive-rail 

of the Outputs. To the right it flows through an over-voltage, over-current, reverse-polarity 

protection(500mA fuse and 6V Zener diode). A side effect of passing through the Zener diode is 

a .37V loss, therefore input voltage should be bumped up by .37V to account for this. From here 

the positive voltage runs to the positive-rails of the Inputs and Analog. Inputs should not be used 

to power anything except your RC receiver.

Higher current loads such as servos should be powered from the power-rails (positive-negative) 

of the Output side. You must use an adequate voltage-regulator to provide power directly to the 

Output power-rails, all servo power leads will attach to these same rails (the signal wires can 

connect on the Analog “S” pins in the case of a camera gimbal). Since JP1 is removed in this 

scenario, the other “side” of the board will need power provided to it’s power-rails directly.

Alternative ways to power your board

3DR Power Module

If you are using the 3DR Power Module please find instructions here: Using the 3DR Power 

Module

 Warning! Under no circumstances should you ever attempt to draw servo power from 

the analog input connector.

 Warning: You may “control” servos from A9, A10 and A11 from the A0 – A11 I/O 

connector, but you must run servo power separately. 

o The A0 – A11 I/O connector cannot supply sufficient power for servos.

o A9, A10 and A11 of the I/O connector come pre-wired to correct digital out for 

use as servo control lines.

o For servo use, it is imperative that they have not been reassigned to analog use 

with the pads on the back of the APM board.

A Non technical Description of the Power

Supply Requirements

The description below simply supplements and provides an alternate view of the information 

above.

1. The APM 2.5/2.6 board has two separate power circuits which make it very easy to 

power by a variety of methods. 

1. A fused power circuit provides primary board and general I/O power: (It cannot 

provide power for servos).
2. The Other power circuit is for the OUTPUT connector power rail: (it can provide 

power for servos).

2. The jumper JP 1 determines whether the two power circuits are connected or separate. 

1. If JP1 is removed, the power rail on the OUTPUT connector “Floats” and may be 

used to distribute power.

2. Although if JP1 is removed the OUTPUT connector cannot be used to supply

power to the APM board.

3. It is possible to power the APM board from the Power Module connector or the 

OUTPUT or INPUT connectors.

4. Normally the APM 2.5/2.6 “Power Module” is used to provide primary APM 2.5 board 

and general I/O power.

5. Alternatively primary board power can be supplied by a BEC either from one of the 

ESCs or from an external BEC.

6. If servos are used, supplementary power is required. 

1. Generally one power supply is provided for the board and one or more additional 

power supplies for the servos.

2. But if a sufficiently large external BEC is used it can supply power for both via 

the OUTPUT connector.

7. Only the OUTPUT connector can provide power for servos as the other circuit is fused. 

1. The address connector is sometimes used provide servo signals, but the servos 

power must come from elsewhere.

8. How you are powering your APM board and or servos determines whether JP1 

is installed or not. 

1. (Whether the two power circuits are separated or connected).

2. All possible configurations are detailed Below.

9. The type of use will determine which options are available. 

1. Copter can power the APM from a power module or a UBEC or a BEC from one 

of the ESCs and can power servos from a UBEC or from the other ESC’s BECs.

2. Plane can power the APM from the power module, the BEC from the flight 

motors ESC or a separate UBEC and can power servos from a separate UBEC or 

the flight motors BEC if it is large enough.

3. Rover can power the APM from the power module, the BEC from the drive 

motor’s ESC or a separate UBEC and can power the steering servo from a 

separate UBEC or the drive motors BEC if it is large enough.

Power Supply Rails Connected Requirements 

(JP1 Installed)

Warning: Do not exceed Abs MAX input voltages when connecting the power supply or you 

will damage your board.

Warning: Connecting USB when you have input voltages at the high end of the range (near Abs 

Max) can damage the board. Disconnect battery before connecting USB or test input voltages so 

they are within the specified range.
Power Options Nominal Abs MAX JP1 status

Power on Output PWM connector 5.37V +-0.5 6V JP1 connected

Power on Input PWM connector 5.00V +-0.25 5.5V JP1 connected

No Power Module and No Servos and Power provided by 

BEC from ESC

 If you do not have a power module and you are not using servos.

 Ensure JP1 is installed and provide the necessary power via the BEC from one of your 

ESC’s.

 Connect one ESC’s BEC power and ground wires to one pair of the APM OUTPUT 

connectors power and ground pins.

 Clip the BEC power leads on the remaining 3 wire connectors.

 Ensure that the ESC’s signal wires are connected to the appropriate APM 

OUTPUT connector signal pins.

 You must ensure that your ESC’s BEC has a sufficient power capability (at least 2 amps). 

o Most 20 amp or higher ESCs have 2 amp BECs.

No Power Module but using Servos and a high power 

External BEC

 If you do not have a power module and are using servos you can use a high power 

external BEC.

 Ensure JP1 is installed and provide the necessary power via a high power external BEC 

(5 to 10 amps or more).

 The BEC power must be provided to one pair of the APM OUTPUT connector pins.

 Warning! Clip all power leads on the ESC’s BECs (they would conflict with the external 

BEC).

 Your servos will determine the size of the BEC required.

 You should allow at least 2 or 3 amps extra to power the APM, receiver and to prevent 

(brown outs).

 All of the positive power for driving each servo must come from the OUTPUT connector. 

o This is true even if the servo(s) signal wires are connected to the ADDRESS 

connector.

 This option requires you to take responsibility for providing sufficient power to prevent 

brownout.

No Power Module but using Servos and multiple BECs from 

ESC’s (A BEC for each Servo)

 If you do not have a power module and are using servos you can use multiple BECs from 

your ESC’s.
 Ensure JP1 is installed and plug one of your ESC’s signal cables with power leads into 

the OUTPUT connector.

 Remove the power and ground leads from the remaining ESCs signal cable connectors.

 Plug the signal wire connector from each ESC onto the appropriate pin on the 

OUTPUT connector. 

o You can heat shrink these or plug them into a multi-wire connector appropriate 

for your copter.

 Connect one pair of each of the remaining BEC power and ground lines to the power and 

ground of each individual servo.

 Clip or heat shrink any remaining excess BEC power and ground leads.

 The BEC power from one ESC must be provided to one pair of the APM output 

connector pins.

 Plug only the signal input wire from your servos into the appropriate OUTPUT or 

ADDRESS connector pin.

 Your ESC’s BECs should be at least 2 amps.

 The ESC’s BEC grounds are in common with battery and internal signal ground so 

grounding the servos this way is OK.

Power Supply Rails Not Connected 

Requirements (JP1 Not Installed)

Warning: Do not exceed Abs MAX input voltages when connecting the power supply or you 

will damage your board.

Warning: Connecting USB when you have input voltages at the high end of the range (near Abs 

Max) can damage the board. Disconnect battery before connecting USB or test input voltages so 

they are within the specified range.

Power Options Nominal Abs MAX JP1 status

Power on Output PWM connector 5.00V +-0.5 6V JP1 open

Power on Input PWM connector 5.00V +-0.25 5.5V JP1 open

Power Module and No Servos

 If you have a power module and you are not using servos.

 Ensure JP1 is not installed.

 Provide the necessary power via the power module connected to the APM’s power 

module connector.

 When connecting your ESCs to the OUTPUT connector clip the BEC power leads on 

each ESC’s 3 wire connector. 

o Or connect only the ESC’s signal wires to the OUTPUT connector.

Power Module and using Servos with External BEC power
 If you have a power module and an external BEC and you are using servos.

 Ensure JP1 is Not installed

 Provide APM board and receiver power via the power module connected to the power 

module connector.

 Connect an external BEC with sufficient power for your servos to one pair of the 

OUTPUT connector power pins.

 When connecting your ESCs to the OUTPUT connector clip the BEC power leads on 

each ESC’s 3 wire connector. 

o Or connect only the ESC signal wires to the OUTPUT connector.

Power Module and using Servos with BEC power from one 

ESC

 If you have a power module and you are using servos Remove JP1.

 Provide APM and receiver power via the power module connected to the APM’s power 

module connector.

 The BEC of a single ESC must provide sufficient power for all your servos.

 When connecting your ESCs to the OUTPUT connector clip the BEC power leads on all 

but one of the ESC’s connectors.

 Or connect only the ESC signal wires to the OUTPUT connector for all except one ESC. 

o And on that ESC connect all 3 wires to the OUTPUT connector.

No Power Module and using Servos with BEC power from 

two ESCs

 If you do not have a power module and you are using servos remove JP1.

 Provide APM and receiver power via 1 pair of ESC-BEC power wires connected to the 

APM INPUT connector power pins.

 Also connect another of the ESCs power wire pair to the OUTPUT connector.

 The BEC of a single ESC must provide sufficient power for all your servos.

 Clip the signal power leads on your remaining ESC’s.

 Connect all ESC signal wires to the appropriate OUTPUT connector pins.

APM Power Wiring Example

Warning: Do not exceed Abs MAX input voltages when connecting power supply or you will 

damage your board.

Warning: Connecting USB when you have input voltages at the high end of the range (near Abs 

Max) can damage the board. Disconnect battery before connecting USB or test input voltages so 

they are within the specified range.

On the bench, you’ll probably be powering the board via your USB cable while you set it up and 

test it. But in your aircraft, you’ll need to power it with your on board power system, which is 
usually your LiPo battery going through an ESC or the Power Module. In the case of a 

multicopter, this can come through your Power Distribution Board (PDB), which will break out 

the 5V output from the one of the electronic speed controls (ESCs) or the Power module which is 

wored directly to the battery.

In the picture below, the red and black wires are the 5b m hV power cable coming from a PDB. 

You can plug them into any two pins along the 5V and Ground (middle and outer) rows of pins 

on APM 2.5’s Output side. The other cable, which in this case is a four-wire cable with orange 

and white wires for a quadcopter, is the signal cable to the PDB, which are the wires that APM 

2.5 will use to command each of the ESCs.

The picture below is of APM 2; but the concept is applicable to APM 2.5.
It’s also possible to power APM 2.5 from two separate sources, one powering the RC system on 

the input side, and the other powering the output side (servos or ESCs). This is determined by a 

jumper on the JP1 pins (see below). If the jumper is on, which is the factory default, the board is 

powered from the OUTPUT rail or the USB. If the jumper is off, the board is powered from the 

INPUT rail, but the OUTPUT rail will need its own power source. This configuration is used if 

you want to have two separate power sources in your aircraft, one powering the servos and the 

other powering the electronics. The ideal input voltage is 5.37v +/-0.0v and may not be provided 

by a typical ESC.

Warning: Do not exceed Abs MAX input voltages when connecting power supply or you 

will damage your board.
In some cases it may be a good idea to set the input voltage slightly above the median (but below 

the maximum) to account for possible voltage drops during momentary high current events.

The APM2.5 by itself draws relatively little current (200ma range) and a power source capable 

of providing 300 – 500ma will provide plenty of margin. However, if servos or other power 

consuming devices are being driven by the same power source you must consider the power 

requirements for those devices as well and provide plenty of margin to prevent disastrous 

“brown-outs”. For instance, a single digital servo can easily draw 1-5 amps depending on it’s 

size and performance. (Note: ESCs do not consume power from the APM) If you experience 

spurious resets or other odd behavior it is most likely due to noisy or insufficient power to the 

APM. As with all logic boards, electrical noise from the motors, servos, or other high current 

devices on the power source can cause unpredictable behavior.

It is recommend that a power filter be used in such conditions.

Too short or long power wires, bad or old connectors, or insufficient current capability of the 

APM power source can result in a “brown-out” situation resulting in unpredictable operation. 

This is particularly true in traditional helicopters where the collective servos can draw 3-20 amps 

in short bursts. The power source must be able to accommodate this without voltage droop or 

voltage spikes. A quality switching type BEC such as one of

these

or one of

these

can be a solution depending on overall current requirements. Many of these type of regulators are 

programmable so remember to program them with in the safe operating range of the APM2. 

Linear voltage regulators are not recommended as they are inefficient and prone to overheating 

and heat induced failures. APM2 should never be connected directly to a battery of any type.

Power source problems are common and can be insidious and frustrating. Be meticulous. Any 

autopilot or flight controller is useless and potentially dangerous without good clean power 

source.

The picture below is of APM 2; but the concept is applicable to APM 2.5/2.6.
Explanation of solder jumper options on the 

bottom of the board

APM 2.5 Board Features

APM 2.5 Board Assembly Options
 Quadzimodo has produced a really nice editable 3D model of the APM 2.5 board in 

SketchUp 8: APM 2.5 Google Sketchup File
Analog input pins

Pin 0 to 8: The APM2 has a row of analog input pins down one side, labelled A0 to A8 on the 

underside of the board. These are available as pin numbers 0 to 8 inclusive in PIN variables.

All these pins can take up to 5V and may be used for any general analog input. They are 

commonly used for airspeed and sonar inputs.

Pin 12: power management connector current pin, accepts up to 5V, usually attached to 3DR 

power brick with 17:1 scaling

Pin 13: power management connector voltage pin, accepts up to 5V, usually attached to 3DR 

power brick with 10.1:1 scaling
Digital output pins

The APM2 uses the same set of 9 analog input pins as digital output pins. They are configured as 

digital output pins automatically when you start to use them as digital outputs.

Pin 54 to 62: You need to add 54 to the pin number to convert from an analog pin number to a 

digital pin number. So pin 54 is digital output pin on the A0 connector. Pin 58 is A4 etc.

These pins are usually used with the RELAY_PIN to RELAY_PIN4 parameters, allowing you to 

control things like camera shutter, bottle drop etc. They are also used as sonar “stop” pins 

allowing you to have multiple sonars and not have them interfere with each other.

Questions about this page? Comments? Suggestions? Post to APM Forum! Use the platform 

specific to your query, and make sure to include the name of the page you are referring to. 

Fixed-wing aircraft UAV

Getting Started

Introduction

Video Guides
First Time Setup

Assembly

Pixhawk Wiring and Quick Start

PX4 Wiring

RC Setup for Plane (APM)

Install Mission Planner

Load Firmware onto APM

Loading Firmware onto Pixhawk

Load Firmware onto PX4

Configuration

Checking the Sensors

Reversing Servos and Setting Normal/Elevon Mode

Throttle Arming in Plane

Failsafe Function

Advanced Failsafe Configuration

Plane Parameters

First Flight

Flight Modes

Tuning the Airframe

Roll, Pitch and Yaw Controller Tuning

Navigation Tuning

TECS (Total Energy Control System) for Speed & Height - Tuning Guide

Calibrating an Airspeed Sensor

Tuning Ground Steering for a Plane

Automatic Tuning with AUTOTUNE

Flight Features

Automatic Takeoff

Automatic Landing

Stall Prevention

GeoFencing in Plane

Terrain Following

Channel Output Functions

Mission Planning & Analysis

Planning a Mission with Waypoints and Events

Mission Command List*

Camera Control and Auto Missions*

Rally Points

Downloading and Analyzing Data Logs in Mission Planner*

Using a Ground Station

Telemetry Logs

Diagnosing Problems Using Logs

Using Python Scripts in Mission Planner

Geotagging Images with Mission Planner

Other Mission Planner Features

Optional Hardware*

Telemetry*
3DR Radio v2*

Bluetooth

RFD900 Radio Modem*

FrSky*

XBee*

3DR Radio — Advanced Configuration*

3DR Radio v1*

Power Modules*

3DR Power Module*

Attopilot Current Sensor*

Attopilot Current Sensor with Pixhawk*

Rangefinders*

Maxbotic Analog Sonar*

Maxbotic I2C Sonar*

LIDAR-Lite*

Lightware SF02*

Optical Flow Sensors*

ADNS3080 Mouse Sensor*

PX4-FLOW*

Cameras and Gimbals*

Tarot Gimbal*

SToRM32 Gimbal*

Gimbal with Servos*

Camera Shutter Configuration*

Camera Trigger using CHDK*

Camera Trigger using Stratosnapper/IR*

Camera Trigger for Sony MultiPort*

3DR Camera Control Board*

CHDK Camera Control*

Minim OSD for FPV*

Servo*

Positioning*

3DR UBlox GPS + Compass*

LEDs*

UBlox GPS Configuration*

Zubax GNSS: GPS, Compass, Barometer*

Relay Switch*

EPM Gripper (EPM688)*

PPM Encoder*

PPM Encoder Programming Guide*

Received Signal Strength Indication (RSSI)*

Airspeed Sensor

Calibrating an Airspeed Sensor

eCalc Motor and Prop Efficiency Guide

AutoPilot Hardware*

Pixhawk*
LEDs*

Sounds*

Safety Switch*

APM 2.x*

LEDs*

PPM Encoder*

PX4FMU*

PX4IO Overview*

PX4FMU plus PX4IO Wiring

Erle-Brain Linux Autopilot*

Use-Cases and Applications*

3d Mapping*

Web Apps*

First Person View (FPV)

Multi-Vehicle Flying*

Antenna Tracking

Mission Planner Antenna Tracking*

Antenna Design Overview*

Appendix*

Glossary*

Wiki Editing Guide*

Archived Topics*

Disabling the Built In GPS on APM2*

GPS Module*

External Compass*

VR Gimbal*

Modes de vol (fr)

MagAPM2 (fr)

Connexion RC (fr)

Capteur de tension & courant (fr)

Carte APM2.5 (fr)

Téléchargement-installation du logiciel Mission Planner et chargement du micrologiciel

Téléchargement du programme

Premier paramètrage de l'APM

Install Mission Planner (Korean)*

Documentation Tests*

Fixed Wing FAQ

Full Table of Contents*

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