There are lots of threads about ESC calibration issues on this forum. I was pulling my hair out but I discovered the problem by writing this forum post. I thought I would share my silly problem to help others avoid the same trap.

I'm using a JDrones Hexa frame with JDrones motors and HK 25-30A card-programmable ESCs. I also got the programming card, but it appears to be non-functional, but that's another issue. I tried ArduCopter 2.4.1 and 2.5. I've reset the APM, cleared the EEProm, setup the radio and have all modes set to Stabilize.

I followed the ESC calibration instructions on the wiki. All 6 ESC calibrated and the motors turn in the correct directions. When I connected to the PDB, and power up, however, I just got continuous beeps. Not the long, one-second beeps, but the shorter (~.25 second beeps). According to the user manual for this ESC (http://www.hobbyking.com/hobbyking/store/uploads/44172390X371547X37...) this means the throttle stick is not in the bottom position.

I've tried many tests, including:

* Disconnecting the other 5 ESCs as, even with ear plugs, these beeping motors are beeping loud!
* Connecting the ESC directly to the RCRx.
Result: it starts up and spins fine
* Connecting the ESC directly to the APM, not using the APM->PDB jumper.
Result: same .25s beeps.
* Arming the APM (powered by separate battery on a separate power bus), waiting for the solid green and then powering up the ESC.
Result: Various: usually incessant beeping, sometimes one beep every 2 seconds ("Throttle signal is abnormal"), and once (out of about 20 tries) the ESCs even powered up and ran normally.
* Connecting a servo to the ESC connections.
Result: servo moves in response to transmitter sticks, movement of the APM.

So what was my problem? I had the RC channels connected to the APM in the incorrect order. I didn't notice from the wiki that channels are connected in order: roll, pitch, throttle, yaw. I had them connected throttle, roll, pitch, yaw. Oops.

Well, it's working fine so far and I've hovered it indoors while the rain continues to beat down.