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Hi all,

Wondering if anyone else has had the same issues as me, and how they fixed it.

Recently burned out a ESC on my previously sweet runnning, reliable hex. Burned out on the ground, so no big deal, but I was out of replacement ESC's (hobbywing platinum opto 30A). The night before a shoot...

So I had to lift the PDB and ESC's from another rig I was in the process of building. In this case, HK multistar 45A opto's. Crucially, bought in two batches, which might be an issue, as you see later.

Anyway, all went in, and hex was rebuilt. ESC throttle positions reset. But it refused to fly. At first, 3 motors refused to respond. I noticed that of the 6 ESC's, the three attached to the non-spinning props had the brake on. These 3 were from the old batch (November 2013). The newer ones (July 2014) were ok. I also noticed that the 3 old ones would not take any setting changes.

I then experimented. I attached JP1 on the APM (I'm powering from a clone PM soldered direct to the PDB)...and bingo. All 6 motors now spun. I reset all ESC settings to No brake, LIPO and High timings. But now, the next problem...It just would not fly. It would just tip over, or vibrating/pulsing wildly. So I checked prop rotations, motor order, ESC timings etc. All seemed ok.

I started tuning down the PID's and RC_SPEED settings...which seemed to work. Eventually, I got it up, and flying. 5-10mins of flight and tweaking later, it was dialled in. End of the pack, but I thought I had it fixed, so went home.

Day of the shoot...fresh pack in...and it's worse than the night before. Again, back to the PID's, RC_SPEED settings...also tried throttle PID's and Stab PIDs. No luck. It even spun out and crashed at one point. But the same thing again...kept playing with the settings, kept testing, and it got slowly better. It was even good enough to get half the shoot done.

But a new pack went in again...and boom, back to the massive vibrations and oscilations. But I found a way to compensate; to gun it to 100% throttle two or three times. That settled it.

Then it twigged - the problem was voltage related. Only when the pack got down to about 3.7v per cell, would it actually flight close to it's former self. At 4.2, it vibrated so badly, it could barely get off the ground.

And now the exception to this. Every time I did an ESC setting change via the radio, I would spin it up....and *every* *single* *time* it was butter smooth at any throttle position or behaviour...not even the slightest issue or glitch. it didn't matter if the pack was full or empty. It was like it's old self. This is important, because this step bypasses the APM. Put the APM back in the loop, and it's a vibrating basket case again.

So...ideas? Not has a lot of responses to my other queries lately, but this one is important, and could really do with some ideas about where to look, in case I've missed something.

Specs for the problem:

APM2.5 (genuine with cut compass trace) on 3.1.5. Has flown 40 hours this year without a glitch.

6 x multstar 45A optos; 3 x new (unflown), 3 x nearly new (flown no problem in a quad).

6 x tmotor 3508-29's. Also fault free.

1 x clone 10S Power module

1 x quadframe PDB

6S maxamp packs (various mah)