SK720 with GPS Caution Crash & Burn

[A VIKING]

Sorry for your loss c99hris.

One thing I have learned and observed over a long career in aviation.
These are constantly advancing technologies.
The creators of these technologies spend an enormous amount of time in research and development to perfect the system before release to the public.

But in the end, one of us, will always figure out how to find that obscure weak point in the system.

It's the circle of life for advancing technologies.
We dream, we create...and we hope for the best.
If the best is not achieved...we repeat the process.

[robertvizzo]

Originally Posted by Skookum

You're right js, I think was tripped off by the incorrect physics. "Someone is wrong on the internet!"

If it had had a GPS lock, it would have rescued it. It was in a fall-back mode. The real question is why it lost lock, the magnetic sensor picked up weird stuff, and sbus lost a few packets, all at the same moment the pilot put the nose down.

People take the risk that everything about the heli is 100% at that moment by "big moves", but that's part of the hobby.

I do not see how you figure flying controlled into a rescue hard deck that cost around $950.00 to purchase with an set altitude at 30 meters is trying to crash the heli on purpose!!!! Your one of a kind Art, 30 meters is plenty time to stop an 80 mph heli from hitting the ground. Even easier if it was on a 45 degree angle. What it sounds like it did was just plain ole screwed up. I know its hard to admit when something you manufactured is flawed but facts are facts. You need to man up and take care of your client who paid hard earned cash for a system designed to work. I also noticed you posted but I think you deleted now, that you believe your client is trying to extort you? That is the dumbest thing you can do for customer service is blame the client. Keep talking and watch your sales plummet.

[SpeedTape]

Originally Posted by robertvizzo

I do not see how you figure flying controlled into a rescue hard deck that cost around $950.00 to purchase with an set altitude at 30 meters is trying to crash the heli on purpose!!!! Your one of a kind Art, 30 meters is plenty time to stop an 80 mph heli from hitting the ground. Even easier if it was on a 45 degree angle.

You are misrepresenting the facts. Please re-read the discussion upthread. Nowhere does it say that the hard deck was set at 30 metres. And your 45 degree angle and 80 mph values are either wrong or irrelevant. C99hris himself says that the hard deck was set at 20 metres and Skookum's analysis of the data in the log shows that the helicopter was descending at a 70 degree angle at a speed of about 105 km/h when it reached the rescue hard floor.

A bit of simple grade 10 trigonometry reveals that the corresponding downward velocity, when the heli reached the hard floor, was about 99 km/h (rounded to 100 km/h by Art). It doesn't matter what angle the helicopter itself was at. It could have been completely level for all anyone knows. The data in the log shows that it was going down at 100 km/h when the rescue kicked in, and that is all anyone has to go on. It pulled 8g's trying to recover but it didn't make it.

Also discussed upthread was the fact that the system was hobbled by a lack of a GPS fix and bad compass data. According to Skookum's analysis, the GPS lost its fix at the same time as the compass heading went weird and the SBUS receiver started dropping packets. They have suggested that the GPS either fell off its mount (in which case the dropped SBUS packets would probably be a coincidence) or that there was some sort of electrical/magnetic interference that caused all three problems to occur at the same time.

C99hris' posts indicate that he was testing the hard floor by intentionally diving below the 20 metre hard floor level. It sounds like he was being more aggressive about it each time he did it. Unfortunately, it seems that he did the last test at just the wrong time. The GPS either fell off its mount or some other problem interfered with the hardware and the system had to rely on just barometric altitude during the recovery. That is all discussed upthread.

It sucks that it happened and a lot of us here on this thread feel bad for the guy. But we also know that, more often than not, the bailout prevents crashes. And as Boomer said, even if it once in a while fails to prevent a crash that would have occurred anyway, you still win because it saved you the vast majority of other times.

In this case, it sounds like C99hris was intentionally playing with fire and got burned by an unforeseeable combination of events. How is that Skookum's fault?

[c99hris]

The GPS was with the crashed Goblin, thus it did not fall off during flight. The only real facts are in the logs which shows the 8g pull up then the full down collective which drove the heli into the dirt. The 8g pull up at less than 20 meters indicates that the system tried to stop the hard deck entry and failed to level then pull up, The logs I would have to say show some of the picture however since the velocity was zero during the 8g full collective pull up its difficult to decode the rest of the story. Just saying the whole story does not add up. Playing with fire would indicate the the hard deck is not as advertised. After switching from the Bavarian Deamon to the Skookum on this machine who would think that the $450 GPS would not work as advertised. The Deamon worked every time no matter what attitude I had put it into. I would not consider this playing with fire as much as I would consider it a test of the ability of the hard deck to determine what it could or could not do. The entry velocity to the deck has been way overstated here, as we all know we can fly these Goblins at nearly any speed and any attitude thus the angle of the nose does not indicate speed. The only real indication of speed was that it too 6 seconds to go 75 meters per the data(if we can believe the data)

[SpeedTape]

Originally Posted by c99hris

The GPS was with the crashed Goblin, thus it did not fall off during flight.

I think they mean that it fell off its mount and was hanging by the wire. Presumably it was still connected to the SK720 or how would it have been feeding altitude data?

[Skookum]

Originally Posted by c99hris

... I would not consider this playing with fire as much as I would consider it a test of the ability of the hard deck to determine what it could or could not do. The entry velocity to the deck has been way overstated here...

The log doesn't include GPS data during the dive, so the horizontal velocity is unknown. It did however include attitude, altitude, and inertial senses. There was an average of roughly 4 m/s2 (0.4G) downward acceleration during the dive. Both the altitude rate and inertial data add up to about -28m/s (100kph) vertical speed. The integrated recovery acceleration also corresponds to a stop from that velocity.

Note that with 20m to go at 100 kph, that left only 0.7 seconds to recover. A good pilot's reaction time is about 0.7 seconds. Robert's FB page suggests he was the pilot.

The Sk720+GPS can normally manage that tight a rescue. But in this case, the logs show the system was half crippled by loss of GPS lock since the top of the 300 foot dive, with RX dropouts and magnetic weirdness after a period of high vibration right before. The high vibs weren't a direct cause, but a clue.

There are dozens of goblin 700's out there flying well with this system.

BTW, it's better to use "soft floor" rescue mode if you are doing high-energy flying, or hard core testing. It adds a buffer that varies with vertical speed and orientation.

[dcope17]

Simply put... There is nothing on Skookum's website saying that the SK720 paired with the GPS is GUARANTEED to save your heli. It is up to the consumer to research and then decide if the want to purchase the SK... Then to set it up and do testing or no testing.
I am one that errors on the side of caution almost always. I tested my hard deck over a 30ft. deep creek ( no water in it ) so that even if the deck was set to 5m, I could test to see if the heli stayed above the dirt. ( I walked into the creek a bit so my eyes were at the level the heli initiated at ) then I tried it.
I happen to never have an issue, but I also knew that if I did crash it, it was going to be on me.
I can't explain the chain of events leading up to the crash, but it crashed.
So now you're at another decision cross roads... Keep the SK or sell it and try something else. No one will blame you for buying something different.
I like my Skookums and I know other at my flying field that have tried them and don't like it. That's just the way it is.
Good luck getting your heli back together and continue flying and enjoy it.

[c99hris]

Actually this was the second flight, the first flight I tested the rescue, hard deck and go home where each worked per the book and per my expectations. As a cautionary move I increased the hard deck from 15meters to 20 for the next flight where my plans were to make a steeper approach to the deck and confirm that all was working correctly. You know the rest of the story.

[WI_Hedgehog]

First Rule (learned the hard way): When anything looks even a tiny bit "off" on a heli, bench it until it's sorted and proven correct.

Second Rule: Check/test everything related to what you're doing three times before you believe it. Use different testing methods to prove previous results.

Third Rule: Results are governed my mechanics, physics, control circuits, and probability. Expectations are not.

nth Rule: Not adhering to the numerical rules is, on average, costly. Whining about it won't win respect, sympathy, or dates with flossy babes.*

Oblivious rule: If you throw blame blindly, expect that sooner or later a pro batter will line-drive one to your face.

Governing rule: Adrenalin will always try to bypass numerical rules and become RULE 0. That's also the number of functional helicopters you'll eventually have if you let it, zero.

Rule of probability: The rules will be observed. No matter your luck, sooner or later the Rotor Reaper will come-a-knockin', and your crash clock will have ticked its last tock.

---
Not sure why the OP is upset about losing a SAB during testing--it was the test platform! Test the Skookum setup on a used Blade 3-D with aftermarket FBL head and 1.) the much lighter heli probably wouldn't have landed so hard. 2.) hard landings are much, much less costly.

I always thought the hard-deck option was a gamble for my flight style and enabled soft-deck instead; that way if I locked up during an inverted mess-o-slop it would [hopefully] have time to bail itself out before my shorts obtained a semi-permanent racing stripe and the heli transformed into something resembling a regurgitated spaghetti dinner.

The G770 parked in the hanger has been wired in a specific manner to reduce electro-magnetic noise, the antennas are positioned to provide full coverage at any angle, the satellite fail-over has been tested and re-tested to ensure signal dropout on one receiver does not affect the flight controller's ability to use another, and so forth. Setup is always checked and re-checked. There are backup power wires, isolated signal wires, top-quality components throughout, and so far, it's still mint, tomorrow, hopefully the same; I don't want to have a fall-and-ball with this one. Check the logs, if they look off, find the problems. Posting one log when everything went to Poland isn't nearly as useful as that plus three previous logs would be.

In the professional world, an inspector would want build pictures, setup documentation, maintenance logs, on-board recorded logs, post-crash pictures, pilot account--so they could figure out what happened! Skookum and experienced people here are trying to help figure out what happened from a very limited view of the whole picture, blaming the flight controller for not saving a craft when there appear to be multiple things going on that may have contributed to the crash is certainly not beneficial.

I own numerous FBL controllers, including SK720BK+GPS, so there's no reason for me to be biased toward or against Skookum except by SK's performance--I can change out to another FBL controller at will.** So far, it's all been incredibly great with Skookum. Like most, I expect a lot of performance for the high price, and they consistently deliver.

--Brad


*For some reason, women never whine about crashes, at least the women I know. They accept it crashed, fix, fly, forget.

**My opinion of Skookum is also based on their products not being a "clone" or knock-off of another brand. I believe pirating another companies work undermines not only that company, but innovation in a hobby I love.

Bacefook - Went to Poland (Official Video) (3 min 25 sec)

[justwannahavefun]

Originally Posted by c99hris

Its a full 8 channel futaba receiver using the sbus output. I had been flying the same receiver before switching out to the Skookum and had never had a loss of signal or going into fail-safe thus my being in denial of the log. My experience with this product has given me a few doubts about the validity of the data. The previous or first flight showed one interval of loss of signal not multiple thus my doubts.

O.K. I think you may be getting a raw deal here. I just had a horrific crash. At the very least, the whole thing started with an altimeter that's reading incorrectly. I think, and I say think cause I'm just not sure, that my crash was ultimately caused by my brain shutting down due to panic mode. That being said, I've never had a problem with crashing before this that started with the heli being upright, and not yawing much at all. All I should have had to do is bring it down. I started at about 40 meters.

So what happened? I hit RTH, which I had used with the exact same set up, one time. It worked great. The following day, I hit the switch for RTH again (Here it should be said that I was pretty damned sure that I hit position hold, but the log says I hit RTH. I should also say that I've watched the GPS mode in the setup software change as I watched it, without flipping any switches. I wrote it off to being plugged in to both usb and battery power at the same time. Which of course you need to have both plugged in to see what you're TX is doing.)

So when I hit RTH? the heli started a heavy positive pitch change and started to climb at full speed. This kind of shook me up. I also had a three quarter turn yaw but I write that off to not having enough tail gain. Anyhow, I turned the switch off and started to bring it down. Somehow, and I'm really not sure how, the heli started turning on it's side. I ended up slamming into the dirt. I can't say it wasn't me. I just have never had a problem bringing a heli down who's only problem was too much altitude.

So the log says, Loss of signal warning at sat port a. I'm not sure how the software works but I will say that I don't have any sats plugged in at all. I use a jeti r9 set to UDI, and have used the GPS for altitude hold, position hold, and RTH without incident. All with the same exact setup.

To continue, the logs also says that I turned on the RTH again for one tenth of a second. Really? One tenth of a second? (As I proofread this I'm beginning to wonder if I have a bad cable?) I've got to stick up for you and dispute another poster at the same time. The other poster said something like, "The log doesn't lie". Well, maybe not, but if there's a software bug it's possible to give a message it shouldn't give. I.E., "If X>=25 output to log, "GPS switch one engaged, position hold."

It is more than possible that the software under the right circumstances may read an odd attitude or variable as "X is greater than 25" and therefore tell the log that switch one was engaged, when in reality it wasn't. Don't say it's impossible because it would be highly improbable for you to be able to know that with an absolute answer. And furthermore, the fact that something has NOT happened to you personally, does not equal, "This can't happen, or, "The log doesn't lie."

I'm sorry but that statement, "The log doesn't lie" is just, well, not a very cool thing to say. To reiterate, my log says I lost signal at sat port a and I do not run any sats at either port a or b. And, my jeti will howl at me it I lose signal as well as logging such an event and I had neither. So IF, the sk720 lost signal, it was between the RX and the connection port where the servos are hooked up. I don't remember which port it is. It may be IO-B or IO-C. Maybe it did lose signal but doesn't have the proper text programmed in. In which case, one could say the log, well, lied.

I'm not terribly old (55) but in my little bit of life experience, things are virtually never black or white but somewhere in between. We all know just how many shades of grey there are.

So before you trash this guy think about the last time you were wrong about something. As Fonzie used to say, " I was Ww ww ww wwrr wwrrr wwwrrrrooo wwwwrrroooonnnnggg."

If the gentleman was really told that the sk720 and gps doesn't work with the Goblin, well, there should be a warning on the ads and packaging. It's hard to see why that would be an issue, but I can say one thing for sure. Helicopters can apparently be very weird with barometric altimeters.

I have a CoPilot II with hard deck. And in order to get a proper altimeter reading, you need to have the input hooked up to about 8 inches of tubing that's mounted at a very particular spot under the rotor wash. Then, the tube is to have a particular angle bent in in. Then you have a plastic flexi hose about an inch or so long. At the end of that you have, don't laugh, a funnel. No shit a funnel.

Now if you don't have all this stuff, according to instructions, your altimeter will get wide swings in the readings. So why I wonder, does the Co Pilot II need tubes and funnels and....well, others don't?

The only reason I'm not still using the Co Pilot is because it finds the horizon by means of infrared cameras. I live in an area where EVERY field is lined with very tall trees. The trees make the rescues very jerky. I never had a crash because of it, but it doesn't inspire confidence. If I lived in an area where I could fly in wide open spaces without tall trees, I wouldn't be bothering with any other types of rescue.

The CP II has a lot of wires and tubes. But it's solid, simple, and cheap, and it's very low tech. It's actually quite nice.

And since I'm chiming in here I'll close with this. If you believe that YOUR skookum set up works well because you haven't made any of the dumb mistakes that others have, you may be invested in fighting for a theory. That theory is this. "If you just set up the skookum and heli correctly you won't have any trouble."

This idea is a very comfortable one. "Well" you say to yourself, "MY heli is set up the RIGHT way". Therefore I need not worry about these ugly crashes OTHER people have. I know, I know, I know. I've been there before and I'll be there again. Just remember, it hasn't happened to you......until it happens to you.

[dogbreath]

This was an old thread, not sure what point you're trying to make. Did you have a question about your crash?

Dan

[Xrayted]

Yes, this original thread and incident happened over 2 years ago, so Im sure the OP doesnt need any more assistance or advice at this point

Justwannahavefun, the "climb" and "yaw" you described when RTH was activated is completely normal. The heli will gain some altitude as it turns nose in and flies back to you. Once it finds home the tail will be tuned back into whatever position it took off in, and then the heli will drop back down into its hold position and stay there. This is different behavior from the original GPS release firmware where it would creep back tail in when activated.

Its sounds like you may have panicked instead of just letting it do its thing, however switching back to manual mode should have placed you back in control, UNLESS you possibly did this with the collective stick too low and it slammed itself into the ground when the GPS was released back to manual control.

This scenario is very easy to accidentally do in the heat of the moment, and I've had to really teach myself to be very aware of where my sticks are before ever switching back out of any GPS modes. Nothing will cause you to crap your pants faster than switching back into manual mode with 14* of + or - full collective on the sticks unexpectedly! These are simple things that can easily get lost when in a panic situation like yours.

[WI_Hedgehog]

The reply is on-topic, @justwannahavefun did a search and found a thread describing a similar situation to his own, all good in my book.

More important, I think we're starting to see a pattern: Autopilot is engaged, large stresses are put on the model, existing issues come to light. The pilot has to recognize the situation, take manual control and perform corrective action in a very short amount of time.

This is not the fault of the FBL, it did what it was programmed to do, then lost signal.

Can't exactly blame the pilot, in a perfect world they would recover, but often they have less than one second to recognize what's happening and make the exact correct corrective maneuvers.

The solution seems to be in a few parts:

• FBL firmware is updated by Skookum with an option to auto-recover when heading below the deck even with loss of signal. Remember the Rx goes into Failsafe mode and cuts motor power, so you see the difficulty in this, as you don't want a bench start if you turn off the TX or pull a wire.
• Pilot hits TH & Range Check on the bench and tugs on the wiring, then checks the logs.
• Pilot meticulously eliminates vibrations and EMF noise during the build and life of the model.
• Builder takes a 2014 post to heart and proves a new setup works instead of making generalized assumptions based on a few observations and desired outcome. This alone quite possibly would have eliminated both crashes.

It's a constant learning process...sorry for your loss, thank you for sharing it.

[PaulsATOM]

Its funny to see grown men try to blame anyone but themselves. Yes it could be the SK's fault and yes it could be the pilots fault. Point is it happened and a 700 is expensive to fix. I crashed my MA Furion 600. It was pilot error. my pinky hit throttle hold and I had NO clue!!! $400 damage. OUCH! Nothing is perfect however the SK720 has always worked awesome for me. I just purchased a HC3sX and sold it again because I read all the crap about not being able to use Sat's. SK720 BE is by far the best FBL. Sorry had a couple of wines. Just my 2cents.

Love you guys

[Luvmyhelis]

I think over the last decade I have seen about every issue, and experienced every failure myself that could crash a heli, with about a dozen different controllers I might add. I have even had $2 to $4k systems setting on my counter that crashed, and I do mean crashed expensive helis that went awry , with the manufacturers replacing them admitting guilt. Nothing is perfect boys! Not even military grade setups costing up to half a mil as we see in the news, causing grief to multi million dollar flying helis and planes. I have lost more $$ in crashes with very expensive one off prototypes than anyone I know! Even with Skookum's aboard. Not only Skookum but with a variety of other systems. Not one has been without problems right off the shelf, many struggled to get to where they are today. All in all. Anyone see me here whining? It is an inherent risk with an inherently risky hobby. It is never 'if' you will crash, but eventually when! Get over it.
The manufacturers, Skookum included, do the best they can with a nasty myriad of uncontrollable variants they cannot control as contributing factors in this hobby.
About 90% or more of the time it is caused by other factors outside their control.
Been talking to the new op here via pms. Good guy!
Congrats on your new gps 2 you picked up for a killer price at HD btw!
The one in question is seeing erratic results as Art has responded to his log. Suggesting internal problems that cannot be addressed here. It needs to go in!
I still say after tens of thousands of flights, and getting to play with quite a few pre release prototypes and parts. Lots of crashing, having helis explode and turn into fire balls and such. Playing with different controllers on identical platforms. Comparing, ect.
I still love what Skookum has given us! And how it performs overall for the $$.
And better yet, the support we can get here in this Skookum section by great guys who still want to help. Remember the HF motto! Respect. LMH