I've a 3DR hexacopter, new. 

It has the PM (Power Module), the PDB (Power Distribution Board) and an APM2.5 with no jumper on jp1.

Online, I've found some instructions telling me that when using the PM, one is to leave jp1 unjumpered, and to plug in the +5v coming from the PDB.


Is this correct?


Yesterday, I USB'd into the APM2.5, and downloaded 2.81 firmware.  So I know it's alive - so far.  Don't want to plug things in incorrectly.

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I just finished assembling the 3DR kit for Quad Arducopter and has the same questionning. The documentation for using the 3DR power module on one hand and the page on optional additions (voltage and current sensors) are not clear at all.

There is the paragraph that I do not understand clearly :

"..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."


As I use the Power Module I was forced to remove the JP1 off the APM2.5. Then I understand according to this copied parapgraph that I would need a second battery to power the R/C ? (while the first one only power the motors through the power module connected to the PDB) Is this correct understanding or not ?


Thx for help


I have a 3DR hexa-B.  With it I have the PDB (Power Distribution Board) and PM (Power Module).  So, I have. two power sources - the PDB and the PM. 

jp1 is not jumpered - so I will need both the above power sources.

My outputs are powered by the two wire 5v cable from the PDB.  Note that the ESC control signals from the PDB also plug into the outputs. I don't know whether this 5v from the PDB, is even used by the APM2.5, when jp1 is out.  Likely the ouput buffering chips are powered from this 5v when jp1 is out.  But the ground in that 5v 2 wire cable from the PDB is definitely necessary, so that the PDB and APM2.5 can share the same ground.

Everything else in the APM2.5 is powered by the 5.37 volts provided by the PM.

I think jp1 is a jumper, that when in, joins the output 5v rail to the 5v rail for the rest of the APM.

thx a lot. Ok so when they say on the wiki "two power sources", they do not mean two batteries but two "wires" or "circuits" from the same battery, right ?

So you use still one battery to power everything ? At the moment I have no extras on my Quad. But later on I would like to add a camera gimbal with servos on it. I wonder if the 5v Cable from the PDB that is connected on the outputs can deliver enough power to these servos ?

If I want a second battery+BEC to power the servos of the gimbal (or other optional stuff besides APM and motors) how do I connect the 5v wires from the BEC of that second battery to the APM ? (on the outputs rail ? If yes, what to do with the 5v red&black wire from the PDB that is already on the outputs ?)



I can only guess - I am a user, not one of the developers.  And I'm  a new user at that.  That said, I'd guess same as you did - put that new BEC 5v line on the outputs.  But you still need to share ground with the PDB - so you still need at least the ground, from the PDB 5v supply.  There's a blurb in one of the setup docs, on paralleling BECs - you might want to look that up.  It says you can get away with parallel linear BECs, but not switching BECs.  So, if one of the BECs, or both, are switchers, you'll have to cut one of the red leads going to your outputs jack on the APM.

many tx

I agree, this stuff is confusing. I can try to explain, but I think i need to get a good diagram together that will really help. In the meantime, think of it like this. In your system you have one source of power, the battery, and its at a nominal voltage e.g of 11.1Volts (3s 3.7V*3) or 14.4Volts (4s 3.7*4). The APM, RX and servos need only a 5 Volt supply. This means you need something that converts the battery voltage from e.g 11.1V to 5Volts. These devices are known as regulators. Each regulator will deliver 5Volts to a maximum number of amps. You can have many regulators on one system. For example the APM Power Module is spec'd to 2.25A. The ESCs each can deliver a 5V from the battery up to max number of amps of 3A or 5A typically. ESCs have this feature to supply 5V since each one has an internal micro-controller that needs power to operate and they usually a have some capacity left over.

The idea is with JP1 off, is that the APM PM powers the more sensitive "electronics" and the power side of servos and motors are powered by the ESCs internal regulator.

The problem with using the regulator in the ESCs is that when the ESCs is under a lot of load the motor & servos it can cause the regulators voltage to drop, and if it's connected directly to APM  (via JP1) it will reset and this can cause catastrophic outcome (brown out). Having a separate regulator connected to the APM/RX  this event is much less likely to happen. Hence the new APM PM powers the APM and RX but not the servos etc.. The servos would be powered via  ESCs connected to the outputs . The power to the outputs comes via the PDB board which the ESCs are connected to. The ESCs have the regulators converting the battery power to 5V.

Again to repeat, with split power regulation helps avoid a board reset due to brown out, so it will be quicker to recover after the critical event.

With all that to answer you specific question of adding a second battery to power the servos, servos can draw 0.4 to 0.5 A when moving under no load (which is more Amps when they have resistance to movement!), you can supply 5V via a BEC to the OUTPUTS Use a (5A BEC for examples), but disconnect the PDB 5V line as you would need to break that connection as it's not the source of power anymore. This would mean the servos would now not draw any power from the main battery just this second battery.

( as a side maybe it's good to remember that a 'power source' can either mean battery or voltage regulator, but the regulator also needs to be connected to 'real' power source ie. battery!)

Well said Bill.  Thanks.

I will be using the DJI F550 frame/board, and the ESC's will be soldered to the PDB. Note: I just purchased the Ardupilot Mega V2.5+.

So, From what I am reading, the following is recommended. ??
1. The jp1 jumper is removed
2. ESC's are powered from the battery (Per APM PM Module connection)
3. The 6 pin conector from the APM Power Module is conectected to the Ardupilot
Mega 2.5+ PM.

Sorry if this was already explained, but I have got to make sure.


What do you mean by PDB?  The bottom plate of the flamewheel, or the 3DR PDB?

Are you using DJI ESCs?  The ones without BECs.

What do you mean b y PDB?  (The bottom plate of the DJI F550 for power distribution - PDB)

- for ESC's and battery connection.

Are you using DJI ESC's ?  I haven't purchased the ESC's yet.  I was planning on purchasing the DJI ESC OPTO's, but to my understanding, they are without BEC's

I am confused per the Ardupilot instructions if the BEC is necessary due to the APM Power Module and cable connected to the ArduPilot Mega V2.5+ PM..



In that case, if you aren't controlling anything but ESCs, the PM will be enough for power.  It's what I'm using on my F450 for power, since I've no servos that can overload the PM. 

The DJI ESCs 3 wire control connectors plug directly into the APM's output connector since they have no BECs.  Also note that they don't require calibration, nor can they be calibrated.

The rcvr is powered from the APM's 5v input rail.

So, you are good to go.



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