Weird Crash

[Planehazza]

So, my Fusion 50 bit the dust yesterday, and so far I'm not sure why...

Immediately, I can tell it rebooted in the air but I have no idea why. I did an aggressive flip using a lot of cyclic, and when I released the input (about 6-8 feet up) the model didn't stop flipping. It then thew itelf into the deck, tail first. This all seemed to happen in a second or so - I didn't remotely have time to hit TH. When I went to get the model, the shock and confusion was still high so I didn't even think to hit TH until I was actually at the model, yet the motor was not spinning. This tells me at least the fail safe (either on Rx or ESC) has kicked in and killed the motor.

It all happened so fast (literally flip, boom, dead) that I can't remember exactly what happened. I'm 99.999% sure the Rx battery did not disconnect. The servos were still buzzing away and the ESC was beeping so I'm pretty sure it was still powered up. The VBar logs indicate this also.









Sorry for the low resolution images, I'll re upload them later.
I'm just getting the CC ESC logs now...

EDIT: Typically, my ESC wasn't set to record Controller Input so it wasn't logged throttle signal from the Rx! So frustrating!

[Grumpy]

Sounds very much like a brownout due to Rx supply voltage sagging under heavy servo load. The error logs indicating low voltage seem to support this theory.

If the Rx browned out then the ESC would reset and would not power up again until re-armed (by going to zero throttle). People often seem to think that 'brownout' is a Spektrum issue but in reality a brownout will happen to any brand of receiver if the supply voltage drops too low.

[Planehazza]

Sounds very much like a brownout due to Rx supply voltage sagging under heavy servo load. The error logs indicating low voltage seem to support this theory.

If the Rx browned out then the ESC would reset and would not power up again until re-armed (by going to zero throttle). People often seem to think that 'brownout' is a Spektrum issue but in reality a brownout will happen to any brand of receiver if the supply voltage drops too low.

Yup that's my chain of thought, but I've never had an issue with this pack before. Granted, it was only its second flight on this model, but it's a light Fusion 50 compared to the much heavier G4 it was on previously without any issue. The G4 is running a CGY750 so there's no logging feature, but the model has never had any issue before. At first I thought the pack had disconnected but it wasn't the case.

This is the battery I have, and as I say, it was fully charged. I charged it only 30 mins before the flight.
https://www.electricwingman.com/a123...s-battery.aspx

2S A123
2500mAh
30C (75A) continuous
60C (150A) Burst

I guess it's possible that it is aging and the battery itself failed to sustain >3.3V but it seems unlikely? I think I'll replace it, or get an ESC with a built in BEC...

In honesty, it's going to cost me £120 or so in parts so I'm really temped to strip it all down and sell it.

[jimmyhorns]

How about a dry joint, or an iffy connector?..

[jimmyhorns]

Especially if you have just stripped it out of an old model and re-fitted

[Planehazza]

How about a dry joint, or an iffy connector?..

Can't see anything, and no loose leads anywhere either...

Over the coming weekend, I'll pull the Y lead out that I made to double check nothing has come undone. I was pretty thorough when I soldered it though.

[waveydavey]

In honesty, it's going to cost me £120 or so in parts so I'm really temped to strip it all down and sell it.

Sell a Fusion 50, you sure Harry. Great model and unlucky with the in but I'm not sure the sell it bit is going to pay off.

[Planehazza]

Sell a Fusion 50, you sure Harry. Great model and unlucky with the in but I'm not sure the sell it bit is going to pay off.

I know what you mean, but getting the parts I need is going to be tricky and I'm sure someone out there could take it for spares, even if it's £20 ha. I don't expect I'd get more than a few beers worth for it, but if I spend £120 on parts, it's only going to revive it until the next crash...

I meant the whole model too. I'm confident I could get £200 by splitting it and selling all the electronics separately. I guess it depends on whether I manage to get all the parts or not. TT gears are going to be pretty tough to source...

[Grumpy]

I guess it's possible that it is aging and the battery itself failed to sustain >3.3V but it seems unlikely?

How did you have it wired? If you used the single servo plug output then that would cause large voltage drop if load was high.

[myxiplx]

That's a significant voltage drop for a 2S lipo, as mentioned above, how do you have this wired? It's surprising how much resistance extra joints can add, and with modern servos you really need at least two connections supplying power into the FBL unit.

Also, what FBL is this? The mini vBar is known to suffer more from brownout problems.

[Planehazza]

How did you have it wired? If you used the single servo plug output then that would cause large voltage drop if load was high.

Single Deans from the A123 going to a Y lead that I made myself.
The battery:




The lead:



I'm not a fantastic at soldering, but it was a nice clean set of joint usings 60/40 lead and good paste based flux. I could strip the heat shrink off and double check it hasn't started to fail, but I'll have to leave that until the weekend I think. The Y lead is configure power directly to the Rx (ch 5) and the VBar and is linked via a single lead to provide signal, indicated by the white line in the diagram. I don't have a photo of the actual wire, but I can get on if you think it'll help...

The A123 pack has two servo connectors also, but they are not used and are securely fastened out of the way of any other connectors or conductive materials.

That's a significant voltage drop for a 2S lipo, as mentioned above, how do you have this wired? It's surprising how much resistance extra joints can add, and with modern servos you really need at least two connections supplying power into the FBL unit.

Also, what FBL is this? The mini vBar is known to suffer more from brownout problems.

See above to the first question

Regarding the VBar, yes it's a mini, running on 5.3.4 Pro. It has never browned out before, and it was previously using a really cheap 2S 1100mAh LiFe pack.

I'm getting really concerned now because I've no idea what has caused this brown out.

[Grumpy]

The wiring looks ideal. I'm out of ideas as to why the voltage went low but judging by the log that's what happened somehow??

Have you any way to load test the battery?

[Planehazza]

The wiring looks ideal. I'm out of ideas as to why the voltage went low but judging by the log that's what happened somehow??

Have you any way to load test the battery?

Yup same. Straight away my mind went to brown out or signal loss which would explain why the motor was dead. It all happened so fast and I was too concerned about the lipos and the stress on the servos so I pulled the cables as soon as I got to the model. According to the Logs, it was definitely power related, and not Rf so the mystery continues...

I haven't really, but I'm going to put it on a 10A discharge and monitor the voltage on the PL8. Best I can do :/ The Rx pack is rated for 75A so unless it's faulty and on its way out, I'm confused as to how even thirsty DS610s could over burden that pack.

[myxiplx]

Yup, mini vBar with a single servo connector providing power, my bet is you'll find that's the problem. Your battery should be fine, and the deans from the battery is also good, and while it could be soldering the known vBar issue is a more likely bet imo.

Mikado have a FAQ about power issues with some servos on the Mini vBar:
https://www.vstabi.info/en/node/1422

And RC Heli Nation recommend wiring your system to provide servo power externally to the Mini vBar:
Mini VBar Power Bus - RC Heli Nation

If you can, see if you can reproduce the issue on the bench. Holding the head to load the servos while moving the sticks as fast as you can may be enough, and if you can reproduce the issue on the bench it will give you much more confident in any fixes you make.

Your power wiring layout isn't ideal, although you're doing the right thing by splitting the deans into two plugs with a Y connector, only one of those connectors is providing power to the vBar and servos, the other is only powering the receiver. That means all your current is being pulled through a single plug that isn't really designed for high currents. Ideally you want two servo connectors providing power to the Mini VBar.

You can wire that yourself easily enough, although there is a Spartan Power Bus which provides two pass through servo plugs, allowing you to provide power to the vBar through two ports while still being able to use them:
Spartan Micro Power Bus SRC-MPB

If I were you I would look to make two changes here:

• Add a capacitor as recommended by Mikado (The R2 Prototyping Buffer Pack is worth a look, it's more expensive, but also provides you with a backup power supply)
• Ensure you have two leads providing power into the Mini vBar

[Grumpy]

Yup, mini vBar with a single servo connector providing power, my bet is you'll find that's the problem. Your battery should be fine, and the deans from the battery is also good, and while it could be soldering the known vBar issue is a more likely bet imo.

As I read it it's not a single plug, it's two.

One wire connects direct to the Vbar, the other wire in the Y-lead connects to the receiver then to the Vbar via the other connections (not shown in photo) between receiver and Vbar?.. On the other hand if there aren't any power (+ and -) connections between receiver and Vbar then I'd agree, another connection to the Vbar is needed. (but in that case you need to have some other wire powering the receiver).

One reason why I much prefer the standard Vbar rather than the mini for larger helis is that the full size has more connections so wiring in dual power feeds is far easier.