The APM 2 Board
The APM 2 board comes from the factory already soldered and ready to have the firmware of your choice loaded by the Mission Planner.
Here’s a quick tour of your board:
Your RC receiver channels will plug into the Inputs and your servos or ESCs will plug into the Outputs. Up to eight channels in and out are supported out of the box, although both of these can be expanded if needed by following instructions later in the manual.
The connectors that are soldered on at the factory should be right for most people, but if you want to add more sensors, there are nine ports on the left side (A0 to A8) for that.
Here’s where to connect optional external sensors and controls (not all are supported by all codebases):
The APM2 schematics and board files are
Alternative ways to power your board
Power Requirements Summary
|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 +-0.5||6V||JP1 connected|
|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 +-0.5||6V||JP1 open|
NOTE: if JP1 open, power is required on both Input PWM and Output PWM
The board comes from the factory setup up to be powered by your RC system, with RC input and output power shared. 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 onboard power system, which is usually your LiPo battery going through an ESC. In the case of a multicopter, this will probably come through your Power Distribution Board (PDB), which will break out the 5V output from the one of the ESCs.
In the picture below, the red and black wires are the 5V 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′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 will use to command each of the ESCs.
It’s also possible to power APM 2 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. 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 6.0V DC of power supply input voltage 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 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 such as
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
or one of
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.
Difference between APM 1 and APM 2
The main functional differences between APM 1 and APM 2 is in the sensors. AMP 2 has the advanced Invensense MPU-6000 gyro/accelerometer chip, which has its own sensor-fusion processor. It also has a high-precision pressure sensor for altitude measurements.
Thanks to improving chip technology, we have been able to combine several other functions into fewer chips, including the USB interface/PPM encoder and switching to digital sensors to omit the analog-to-digital converter chip in APM 1. Fewer chips means smaller, cheaper boards, and fewer things to go wrong.
If you’ve previously had an APM 1 board, you will also note a few external differences, mostly designed to make the board smaller and more reliable:
- Formerly external sensors, such as the GPS and magnetometer, are now built in. No soldering or cables required!
- No CLI (Command Line Interpreter) switch. The CLI, if needed, is now invoked in software (hitting “Enter” three times in a terminal at startup) rather than with hardware.
- No relay. Very few people used this, so if you want one (to trigger a camera, for instance), we support adding one externally.
- No DIP switches. All the DIP switch functions (channel reversing, setting elevon mode) are now handled in software by the Mission Planner.
- No on-board power regulator. You must power the board via USB (on the bench) or your regular ESCs (via the ArduCopter power distribution board) in the aircraft, with power coming in through the APM 2 Output pins.
- No voltage monitoring built-in. Most people find current monitoring more useful than voltage, so we now recommend theSparkfun current sensor
, which can be plugged into one of the sensor ports
Power protection kit set up instructions (through-hole diode and fuse included with APM 2.0 board):
Power protection kit schematic drawing:
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.