Naza2 Cinestar8 backflip on takeoff

[JumpinJiminy]

So I know this sounds suspicious, but...

Had a very strange (and very bad) crash this morning where my Cinestar8 took off and flipped over backwards about 4 feet off the ground. What's really odd about this is that this was probably the 20th flight with this setup and the first 19 were perfect. I checked everything prior to launch as I always do and found nothing out of the ordinary: GPS mode, plenty of satellites, fresh batteries, everything nice and tight, etc. Sure was shocked at this behavior. Any ideas?

For background, here's the long and boring story of how this all came to be. About a year ago, after flying the original Phantom for 100s of flights, I decided I wanted something better than a GoPro. An experienced guy said to build, not buy, because you will crash, and if you build you will know how to repair. So I did.

First build was a Cinestar8 clone from parts ordered from Famous Hobby. Used decent parts all the way around, but went with Naza2 FC because I don't believe DJI's hype about Naza2 vs. WKM vs. A2. Was worried about fly aways, so didn't even connect GPS. Flew in atti only, but bird was not very controllable. Got frustrated and gave up, although never had any crashes and machine is still in great shape today.

So about 4 months ago, I bought a used Cinestar8 hoping it would be a shortcut to success. It was a Quadrocopter stock build and had 2-axis servo gimbal. Was said to be in perfect working order with all MK electronics, etc. Got it home, test flew it, was a disaster. Thing was totally uncontrollable. It was all I could do to keep it from crashing. Did a couple of very scary flights, then tried to adjust some of the MK parms a little. Searched all over the web, but all I found were a lot of folks that said they too had no idea what all that crap did, and likewise had very little success adjusting things. Made a couple of tiny adjustments, test flew it, crashed. Damage was limited to a broken landing gear and a bent prop.

Had enough of MK, so I gutted the CS8 and totally rebuilt it using Naza2 FC, Maytech 40A ESCs, AR8000 rcvr, etc. Basically same electronics as on my big clone. To my great surprise, when I was all done and ready to test things out, this bird flew beautifully. It was even better than the Phantom: super smooth, easy to fly, just perfect. I loved it. Test flew it many times, then added the gimbal. Still flew beautifully. Always flew in GPS mode, but had ATTI and Manual available on my xmtr. Tried those modes and they worked well too, but always flew in GPS otherwise.

As I said, I had been flying this with a 5D2 on the 2-axis gimbal for AP (no video for me, just stills). Worked perfectly, was very happy. Had made maybe a dozen or so actual photo shoot flights with it, and everything went perfectly. Today was just like the last time I flew it, so I was expecting similar success, but got a disastrous crash instead.

So given that this had already flown many times perfectly, what could possibly have gone wrong? It can't be props in th wrong direction, or ESCs not calibrated, or any of the things you think of when a maiden flight flips. If it were something like that, it would have never flown in the first place. When I started the motors, all props were spinning, I had full voltage, everything looked good as I moved the throttle to full for takeoff in GPS. Then the backflip and crash onto gravel with much destruction.

So I would much appreciate any ideas folks might have as to the cause. I certainly don't want this to happen again once I get this thing (or more likely my clone) flying again. I realize DJI claims the Naza2 is no good for big MRs, but honestly this CS8 flew like a dream - a million times better than with MK stuff, which I found unusable. And I was using default gains too.

Also, I'm worried about repairing it because I don't know what can be safely salvaged. The props are toast, some of the booms are broken, I have no idea what shape the motors are in, nor do I yet know how the center plate and electronics are (visually they look fine, but who knows). It might be best just to trash this stuff and start over. I wouldn't want to try flying with marginal components that will fail in flight.

Honestly this is very disappointing because I was loving the CS8 with DJI electronics. It worked well for a little while. Sure would like it to work again. Thanks for whatever suggestions you can provide.

 

[jfro]

I have a Naza V2 w/ gps that started a year ago on a small quad, graduated to a big quad, and then a few months ago went to a big x8. Bout 19-20lbs. Flew and flies very nicely on all 3. Talked to a dealer who is in Hollywood area, and he says he has plenty of clients flying bigger birds on Naza V2.

I have never flipped my Naza, although I did my Hoverfly on x8 last year a few times, so don't have a clue what is wrong. I do know, I never launch in GPS mode. Mostly ATT mode except when I forget to flip the switch. Because of some issues with fly aways etc, and the fact I can't afford to lose the rig with expensive camera/gimble, etc, I don't fly long distances and don't fly crazy. ATT mode works great for that with GPS as a rescue mode if I lose orientation or some other issue.

Hopefully, maybe someone else can shed some light. My only question did you get 2 sets of green flashing lights and have you calibrated lately or did you launch very far away from you last launch? Just guesses on my part. I always do the spin the bird horizontally and nose down when ever I go to a new location and always wait for 2 sets of green flashes.

As to rebuilding, I'd fix the Cinestar. Take it apart, check everything for cracks, warpage, & any other damage. Inspect motors for dents, clean the motors as best you can and the test for weakened or messed up bearings or bent shaft. Take em apart inspect the windings and inside the housing. If the motors spin cleanly and there is no play in the housing, then they are probably ok. Check each motor/esc combo by running them.

After rebuilding, I'd leave gimbal/5d camera off, and assuming they weight about 5lbs or so, I'd put 5 lbs of weight on the cinestar and take it out and fly it keeping it maybe 10-15 feet in the air. Let it hover for the a battery. Check motor temps and esc temps. If all ok. Do another flight with some easy flying. Do that 1/2 dozen times or more checking the motors for play, checking temps etc..... If all sound good, then go fly a couple more flights (with weights) and fly it a little harder. If still OK, I'd put the camera on and go take some pictures.

Anything that is suspect, change. Check your wires, bullet connections, esc. Your Naza you can check on your computer. Do a complete setup checking it with your radio.

I'm no expert, so wait and see if others give similar advice It's just what I'd probably do after having built 4 MR's and finishing my 2nd year of flying. Not a novice, but no expert.

 

[JumpinJiminy]

Thanks for the reply. I did have 2 flashing greens at launch. Having come from the Phantom background, I learned in GPS (of course), then flew mostly in ATTI, and even tried manual (but on the Phantom that was hard because it was like trying to tame a wild horse). On the CS8, I fly GPS exclusively, but have a switch on my DX8 to get me to manual if a fly away starts (never had a problem, but only ~20 flights, so who knows). I did fly the CS8 in ATTI and Manual during some early test flights just to make sure they worked. I always laughed about how well GPS worked with the Naza because hovering perfectly still is something the MK seems to have trouble with (according to the forums) and it worked perfectly on my CS8.

I did not compass calibrate, but never had before (except when setting up the thing after re-wiring it), and I'm only a few miles from where I calibrated. I also flew it last weekend during the end-of-the-world flare event that everyone was warning about and had zero issues: five flights that day, all perfect. I would think that a compass error might make it fly funny (not follow commands very well), but would probably not flip it over on takeoff. Just FYI, I was super lazy with my Phantom and never bothered following any of the precautions with it; never had a crash that wasn't just stupid pilot error from being overly aggressive.

I know the Cinestar is pretty much old school now, and almost all of them fly with the MK setup, which I really wanted to learn and love, but just had a bad experience with. I have to admit that I was shocked at how well the CS8 flew with the Naza2 - it was just like a Phantom, but smoother. And the motors never got hot, even with the load. Also, I am flying with 2 6000maH NanoTech batteries and get about 12min (theoretically) fully loaded. It seems like a really solid platform for what I use it for (DSLR still photos).

My flights are typically very short, about 3min or less. I just get up (to about 25m), get the shot, get back down and land. Each flight pulls about 1000maH out of each cell, so I do 3 flights on a set of batteries and then swap to a fresh set.

I'll probably do as you suggest and rip this beast apart to sort out the junk from the salvageable parts. Replacements are easy to find and pretty cheap. In the mean time, I'm going to try to get my big clone to fly a little better. It is 1100mm vs. 900mm for the CS8, and is 6s instead of 4s. It flies okay now that I hooked GPS up (I originally left it off fearing fly aways and only flew ATTI), but still wobbles a bit when hovering, which is bad. It's way overpowered with no load. I have yet to hook a gimbal to it, probably won't until I get it to hover without wobbling.

Sure wish I had a working theory on the crash. Did an ESC go bad? A motor? The FC fail in some way? Without any diagnostic data, there is no way to know. I guess that's where the MK setup shines, but you have to be a rocket scientist to use it. Now I'm a little scared to fly my big bird since it too has a Naza2.

My theory (hair-brained, I know) is that all the DJI FCs are basically the same thing, possibly with slightly different firmware and packaging. I heard that the Naza2 is just a WKM with the waypoints removed, but who really knows for sure? In any event, their pricing is unattractive for anything other than the Naza2. Also using iOSD-mini, for what that's worth. FC mounted on top of moon-gel on a board in the middle of the copter too.