Mystery power failure

[Ian_R]

I had my 700e crash on its first flight after a rebuild. The rebuild was as a result of an Align 700MX 510KV motor failure which also think caused a power failure and a heavy but level landing.

I replaced the align motor with a Scorpion ultimate 4525 520Kv motor, replaced all the broken parts during the rebuild and was flying gentle circuits at low headspeed to then take the heli home and check it over.

However, all of a sudden, without warning, the nose went up and the heli completely shut down and thankfully went in on its side into some long grass.

In the Align motor crash the ESC log showed the temperature spiking to 700deg, in the crash I cannot see anything unusual in the motor log.

My question is; could the motor failure have damged the ESC (Castle Phoenix ICE 120HV) in some way, that could result in it causing the FBL (Helicommand HC3SX) to shut down ? Or with the opto-isolation is this impossible ?

Note; I was going to treat this heli to a new Hobbywing 160HV ESC next month !

[chrisleematt21]

700 celcius? That's a wee bit high. If it did get as hot as the log shows I would imagine it would cause all sorts of problems.

[Ian_R]

It was fahrenheit, but its still a high enough spike to cause issues with the ESC (I'm surprised it still works TBH), but my question is, could the issues extend to the FBL unit ?

[trillian]

I wouldn't think it would be able to affect the FBL controller because I assume the only connection to it is the throttle. What do you have powering the FBL and servos?

I once had a Hobbywing ESC catch fire and it did not damage the FBL unit RX power on that heli was from a separate 2s pack and a regulator. (the fire was caused by a motor wire short - the motor was fine afterwards as well).

I think you'd have to ask Castle on this as that does sound pretty extreme!

[Ian_R]

I've got a separate 2s lipo & a opti ultra guard. Nothing (ultra guard, FBL, Sats) was showing an issue. One cyclic servo was jammed but this was due to the impact breaking the case.

[trillian]

So did you not have control when it pitched up? If you had RX power then it sounds like a signal loss or corruption, but in light of the previous motor failure that would appear too much of a coincidence.

[Ian_R]

No control whatsoever, and I agree that surely it cannot be a coincidence.

[Grumpy]

As you said yourself, the ESC has optical isolation between the HV side (that the motor is connected to) and the LV side( that the FBL/receiver/servos are connected to). It pretty much inconceivable that a fault in the motor could have an effect on the LV electronics in these circumstances. In any case if a fault had been caused then this would have been apparent after the crash.

If this was the first flight after a crash then could it have been some mechanical issue, maybe a link had been loosened and popped off, a screw came out, or high vibrations due to some undetected damage knocked out the FBL.. There is lots of potential for 'undetected damage' following any crash.

[Ian_R]

That's always the problem with crashing; the undetectability of what the issue was before the crash !

[cycled]

It could be signal loss then? What radio and receiver are you using?

[Ian_R]

Signal failure of some description is what it must have been. I'm using a Dx8 and DSMX satellites.

[Grumpy]

A flying buddy used to fly with a BD-3SX and Spektrum sats and he had nothing but problems. It was intermittent, it only happened once every few flights but he would keep getting 'brown-outs' where there was a momentary total loss of control. After a second control was regained but the motor had to re-start which meant the heli would loose a lot of height and had a few heavy landings as a result.

We tried adding capacitors, changing the ESC, adding an external BEC, checked and re-checked everything, you name it, nothing made any difference at all. Turned out that his experience is far from unique. Consensus is that the internal power supoply in the 3SX has difficulty maintaining an adequate supply to sat receivers causing them to brown-out occasionally. I seem to recall that BD's response was that they dont recommend using sats (even though they provide ports to connect them!). BD actually say in the manual that when using sats a minimum 5.5V supply is needed, that's not easy to maintain especially if you are using standard servos that operate on 6V max. We found even with a castle BEC set at 6.2V he still had problems.

The fix in my flying buddies case was to run a 'full' receiver and ditch the sats. The new SPM4649T might be a good option because it's tiny, it has single line SRXL output and dual antenna diversity.

[Coxy]

This is interesting as I think I've had the same issue with the same motor, esc set up. Mine died as well for no reason, I'm still to plug it in to look at the castle log. Bloody annoying as it was flying really well, my question is could the hot temperature over the weekend have some bearing on the crash?

[myxiplx]

I've heard the same with BD and Sats actually, it's not a recommended combination.

[Ian_R]

In 5 years of flying with BD & sats I've never had a problem. Both my 700 machines are on 2s lipos straight into the FBL unit. And I had no problem with my 700n & 550e (which runs off a 6v BEC) the same day.

I've given up trying to find the root cause of what happened, once I get it rebuilt It'll be hovered for 5 mins to see what, if anything, goes wrong. However finding the parts I need especially Align 690 3g blades and Align 105mm tailblades, plus a new clutch liner for the 700n is proving a real nightmare.