Two crashes within one week

[popokatepetl]

90 flights without a single issue and then two crashes within one week. I should take a break I think.

First one was because of the CF skids on the asphalt = bad vibrations which confused FBL system and heli did a roll on the ground @ 2100rpm
Cost 200USD (w/o blades)

Second crash was actually the very first flight after rebuilt. 10 seconds flight and I'm back on the ground. The reason was my tail pulley's set screw got loose. I don't know why as I've used a lot of Loctite two days before the flight so it was cured enough. Only 10 seconds flight? What the hell happened there?
Cost 350USD (w/o blades)

What was demaged in both cases no matter how hard it hit the ground:

- frames
- skids

All I can say is that even if both crashes were really bad it wasn't that bad. I think the repair cost is at least 1/3 less then repairing my Trex 700. Insteresting, isn't it?

[blueprint]

Sorry to hear.

For what it's worth i fly my Goblin off asphalt or concrete and never had the same issue you described. Also, checking the tail pulley screw as well as the main pulley screws should be in your preflight.

Good luck!

[popokatepetl]

Originally Posted by blueprint

Sorry to hear.

For what it's worth i fly my Goblin off asphalt or concrete and never had the same issue you described. Also, checking the tail pulley screw as well as the main pulley screws should be in your preflight.

Good luck!

I landed at 1800 and chnaged to 2000rpm while sitting on the asphalt surface. That head speed change caused some bad vibrations which confused FBL system. It's not vibration but more oscilations form the hard CF skids.
It's common issue with every FBL system. Never do that!

[Mystic3D]

Sorry about that. Ouch!

I have gotten into the habit, bad or good, not sure of just auto from a few feet when landing. Takeoff I don't even wait for the spool up to complete before I get off the ground.

[amitt]

Originally Posted by popokatepetl

I landed at 1800 and chnaged to 2000rpm while sitting on the asphalt surface. That head speed change caused some bad vibrations which confused FBL system. It's not vibration but more oscilations form the hard CF skids.
It's common issue with every FBL system. Never do that!

i am not sure i understand this. so taking off on asphalt causes more vibration?

[OnTheSnap]

Sucks! Mine went for a bad bounce yesterday in the middle of some smack stuff. Felt like a momentary Spektrum sat brownout. Chucking my WR BEC and hooking up a LiPo now. I don't think there is any BEC on the market that can reliably handle 4 HV servos now.

[silas3d]

Originally Posted by OnTheSnap

Sucks! Mine went for a bad bounce yesterday in the middle of some smack stuff. Felt like a momentary Spektrum sat brownout. Chucking my WR BEC and hooking up a LiPo now. I don't think there is any BEC on the market that can reliably handle 4 HV servos now.

+1 I fly straight lipos on anything over 550 sized. I've been using Turnigy nano-tech 2200 35-70C packs for a while now. They're small, light, and inexpensive.

In my mind the increased reliability has always outweighed the small weight penalty (sorry for the bad pun... )

[justindewoody]

I also had ANOTHER crash on Sunday. I lost radio contact during a loop, and when I came out of the loop, I lost radio contact somehow (telemetry showed 9 frame losses!) and it went in...not too hard though. I lost the blades, tail blades, pitch links, one skid, and the tail fin. The boom is fine, and the canopy is still decent. This is a tough bird...in my experience (2 crashes now).

[Chris Sexton]

Yeah I have had more trouble since I got this heli than for months prior, but I think that is because it makes me want to push myself

It does crash well. I haven't had any frame issues in my two incidents, but I did kill a boom. I guess they aren't designed to eject when used as a pole vault.

[blueprint]

I made my setup simple.

HeliJive with the Internal BEC running 6V in all servos. No problems.

[Tmiedema4]

+1 heli does crash well.... I had a boom strike and frames made it out just fine crash cost was 360 with boom and canopy being replaced.

Sent from my SAMSUNG-SGH-I717 using Tapatalk 2

[CeeveeSiN]

saw Justin's crash in person and it went in what looked like very hard.. and still very minimal damages..

I'm flying a Lipo straight on mine.

do not trust BECs at all.

[edsel.labao]

Originally Posted by OnTheSnap

Sucks! Mine went for a bad bounce yesterday in the middle of some smack stuff. Felt like a momentary Spektrum sat brownout. Chucking my WR BEC and hooking up a LiPo now. I don't think there is any BEC on the market that can reliably handle 4 HV servos now.

Were you running the WR on 12s? or 6s?

[OICU812]

6 machines all WR BEC all HV MKS servos all way around not a single hitch so find that odd. All mine are running direct 12s.

How do yOu know it was a brownout satts blinking? Wires all good? What did log say any errors to show cold start or reset?

[OnTheSnap]

12s, but I can make it happen on 6s as well.

The issue usually manefests as antenna switches which normally is ok. But occasionally it hits both and I loose control for about 1 second. It's not a full brown out. Just a very quick transient that causes the sats to flicker. The weak link appears to be the vBar 3.3V regulator to the sats. The sats have very little tolerance to transient voltage spikes.

I suspect if you use an external RX it may not manifest.

Needless to say, I will not use another BEC with HV servos anytime soon. This was not a fun process debugging. And it's working flawless now.

I do know the guys flying the Logo 700's all dumped their WR BECs for Lipo's as well on their HV servo setups. Not reliable for them either.

[edsel.labao]

What is the difference with a 2s lipo vs regulated 8.4 on the vbar 3.3 volt regulator? I would think the lipo would dip on voltage more when the servo draw is high compared to the WR Bec. Kyle Dahl was running 8.4 on his extremes with all HV servos using the wr at 14s with no issues per Dave Dahl in one post I saw. Just curios since I am building another whiplash with a WR bec at 8.4 using JR8917hv and bls256

[OnTheSnap]

Originally Posted by zoomtt

What is the difference with a 2s lipo vs regulated 8.4 on the vbar 3.3 volt regulator? I would think the lipo would dip on voltage more when the servo draw is high compared to the WR Bec. Kyle Dahl was running 8.4 on his extremes with all HV servos using the wr at 14s with no issues per Dave Dahl in one post I saw. Just curios since I am building another whiplash with a WR bec at 8.4 using JR8917hv and bls256

Your question requires a deeper discussion on buck DC/DC converter design which my thumb isn't willing to do at the moment. But in a nutshell a DC/DC is a control system with a fixed response time to either changing currents or voltage. Typical response time is measured in uS and a value of 30uS is typical. When a transient occurs, voltage dips and the DC/DC eventually detects this. Many factors dictate the transient response including the controller design, sense location, and the components chosen (FETs, caps, inductor).

A battery is a much simpler thing and a high performance high C RX LiPo can have much less drop out.

To complete the picture the vBar takes the main voltage input and likely uses a LDO to create a 3.3V bus for its own uController as well as the Vbar sats and Sensor II port. The components on this rail each have their own operational voltage range. My experience is that the sats are very sensitive to any voltage variation and quickly reboot (1s) if they see any disturbance.

With some HV servos I can make the sats flicker at 8.4V with a War bec, but not at 6V. With servos the higher the voltage the faster they operate, and so they use more current and require a more robust power supply as you increase voltage.

Not all HV servos are the same. Some are much harder on the power source than others so your mileage may vary.

I had major problems with 3x 9188, Align 750H on the Goblin and 3x Align 700h, 750h on the 700e at 8.4V. The problem was subtle enough to where it was hard to replicate on the bench and would only manifest during maneuvers with pretty extreme servo loading. In one case this caused me to crash. But most of the time when it hit I could recover.

Yes Kyle had a WR BEC on the extreme which worked with the servos he used then. But on the L700 the WR BEC's were dumped.

[popokatepetl]

And that's the reason I'll stick with Futaba's BLS servos.

[CeeveeSiN]

Originally Posted by popokatepetl

And that's the reason I'll stick with Futaba's BLS servos.

all HV setups pull about the same. Futaba is no less power hungry than anything else.

[OnTheSnap]

Originally Posted by CeeveeSiN

all HV setups pull about the same. Futaba is no less power hungry than anything else.

Not true. It's highly dependent on the motor and controller design of the servo.

He said Futaba BLS not HV anyway. And anyway assumptions are no good here. A Futaba HV servo may be better or worse than mks. But without data we know nothing.