Help me understand servos?

Apologies for being dense on this, my brain just isn't grasping this.

We have a hexcopter with an APM 2.6, power supply, lipo battery.  Its currently wired battery > power supply > apm > out.  I have also ran the 5v out from the power supply to the apm.  JP1 is pulled. Motors work, electronics work, everything works great.   

Now its time for the servos.  We're using a Tarot X6 frame which has retractable landing gear.  This uses a servo input from the APM to control it.  Which output on the APM should I use?  We will also be using a gimball which will need 2 outputs.  We are using an 8 channel Futaba receiver if that is useful info.  I've read probably 20 pages on ways to hook this up and my brain just isn't processing it.

Next question which will probably help me understand my first question:  Why do I need to run power from the BEC to the APM if I have servos?  Its already getting +5V from the power supply, why do I need +5V from the BEC?  I understand the 6S battery is putting out 22V and that needs to be knocked down to 5V for some things, I get that.  But why do I need 2 different +5V inputs?

Thanks for any help.

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  • Josh,

    I wrote a little blog entry when I wrestled with this problem on my Tarot 650s. Might help

  • Sorry.

    Which output to control the landing gear servo?
  • Because the power supply that feeds the APM will not supply sufficient current to both the APM and the servos at the same time. Once the demand from the servos comes on, voltage can drop enough to "brown out" the APM, thereby killing your copter if it happens to be flying. Putting a separate BEC on the output rail while JP1 is pulled allows for a separate power to the servos, without the likelyhood of it affecting the autopilot itself.

    • That makes a ton of sense.  Thanks!

      So which output on the APM would be best?

      • For powering the output rail? IIRC any output that you're otherwise not using. Check with the wiki.

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