S800 (w/15) sudden rapid descents... any ideas?

skivvie

Member
Crashed my S800/Z15 a bit ago while trying to work out a bug that I noticed during my last shoot. Super lucky I was low to the ground ... and the bug I was trying to sort out is exactly what caused me to hit.


I keep getting sudden rapid descents. It seems to only be when throttle is below 50%, and as I confirmed in testing today, I can't see how I'd be hitting 10% as I was looking at my throttle stick at no less than 25% and it happened. I also triple checked throttle curve is linear. It's not battery related as It's happened on all three sets of LIPOs I use. So I'm stumped.


I'll be descending usually around 20-30% and the S800 will start to drop rapidly to the point where I have to give it full throttle to recover. Then all seems fine. It's exactly what I would expect if I went below 10% throttle, but that doesn't seem to be the case. I was testing this today low to the ground and it happened, front of the landing gear clipped the ground before I could throttle out and as I killed the motors it turtled forward. I was fast enough to have the motors stopped before the props hit. Zenmuse was pulled from it's rubber hangers and luckily I had the Rx connected with servo extensions that just popped out. No prop damage and nothing broken... Z15 still works fine. I have footage but no time to post it right now. I have the footage of it acting similarly on my previous shoot as well.


I'm supposed to be shooting a proof of concept with a DP tomorrow to confirm it can do what he wants for a larger project... of course.


Any ideas?! The only thing I can figure is that I'm going below 10% throttle and not realizing it, but looking at the stick, that doesn't seem to be the case. I just can't figure it out and I'm now scared sh@#$less to fly this thing if it's going to drop out of the sky, especially in front of a future employer.
 
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DucktileMedia

Drone Enthusiast
Anything to do with faulty esc? Maybe try a different cutoff mode? Is your voltage fail safe enabled? If so turn it off.
 

skivvie

Member
Wouldn't seem to be, it's stable, not like one ESC causes it. Can't change any of that on the S800 ESCs. Happens with full packs so not cutoff related anyway.
 

DucktileMedia

Drone Enthusiast
If you want i can send you the old firmwares to try. i think someone tried uploading a link to all the odl ones. i would go back to 5.06 or 5.08. Sucks though, as it's always when you need it the most when things act up.
 

skivvie

Member
Question: could this be due to shoddy batteries? I dismissed it at first because I've been able to power out of it. But.... If my Zippy 25C lipos can't handle the draw... Hm
 

DucktileMedia

Drone Enthusiast
I'm using 25c gens ace on my heavy lift octo without issues. Some batteries are not rated accurately though. Probably not what the problem is but certainly worth trying another set.
 

jhardway

Member
I know this may seem to be a pointless question, did you check you throttle input rates in the assistant software, as stated, you may not be going below the 10% on the stick, however it may be doing in the transmitter output, you may have to recalibrate the throttle input with the assistant software.

hope you find it, if so let us know.

cheers
 


skivvie

Member
I know this may seem to be a pointless question, did you check you throttle input rates in the assistant software, as stated, you may not be going below the 10% on the stick, however it may be doing in the transmitter output, you may have to recalibrate the throttle input with the assistant software.

I haven't checked in the software but I did check in the monitor on the Tx... good call though I'll check that now.

UPDATE: Checked and that doesn't seem to be it. At this point I'm assuming I was putting it below 10% and not realizing it... because nothing else seems to make sense. Though I'm still not convinced that's it.

Dumb question... What is your "cut off type" set on in the assistant? Is it set on Intelligent?

Intelligent.
 
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Tahoe Ed

Active Member
With Intelligent you have several seconds before the motors shut off. There is one user that has a Tx mix that limits his minimum throttle to more than 10% so he can never go into motor shutdown even if the stick is bottomed.
 

skivvie

Member
With Intelligent you have several seconds before the motors shut off. There is one user that has a Tx mix that limits his minimum throttle to more than 10% so he can never go into motor shutdown even if the stick is bottomed.

Yes... I've done the same though not enough to fully block out the 10%. Just put the EPA on the low end up so that it's more like 5%. Finally have some time tonight to do some more testing. We'll see.
 

Bartman

Welcome to MultiRotorForums.com!!
how hot is it outside? Zippy packs suck above about 87 degrees or so. I've got six 5800 mah 30C packs and they are actually more like 15C packs when it's really hot outside. I nearly crashed a few times until I realized this about the Zippy packs. Are you at a high elevation in Draper? High elevation with high temps would likely make your Zippys wish they were in a cold storage facility in China still.

Bart
 

skivvie

Member
Interesting. I'm at about 5500 ASL here... and same with most of my filming. High desert or high mountain. Temps are 85-95F.

Dunno though. The fact that I could power out of the descents makes me rule the batteries out... don't ya think?

how hot is it outside? Zippy packs suck above about 87 degrees or so. I've got six 5800 mah 30C packs and they are actually more like 15C packs when it's really hot outside. I nearly crashed a few times until I realized this about the Zippy packs. Are you at a high elevation in Draper? High elevation with high temps would likely make your Zippys wish they were in a cold storage facility in China still.

Bart
 

Bartman

Welcome to MultiRotorForums.com!!
hmmm....good question. i had repeated brown-outs of my FC which were making the heli wander all over the place until I could land. after a short break I could take off and fly around a bit more until it got wobbly again and had to land. with other packs it was fine.

are you able to bottom out of a fast descent and then continue to fly or is that where the problems will start?
 

skivvie

Member
Yep. When it happens, and so far I haven't been able to pin point it, I'll get a rapid descent... which I power out of, then it flies normally from there. I need to go back through the video's and pin point the drops and up a cut so you can see it. Swamped with other work at the moment.
 

RotorTalk

No Longer Active
I'm getting exactly the same thing in Atti Mode. The Naza GPS flies well for the most part but about 0.75 into battery's life I have phases of yo-yoing/rapid descents which I can power out of.

RELATED?: If I yaw hard right in Atti I get a Pitch/dip to forward-right too.

XAircraft X650V2 Quad
Naza GPS, Controller mounted on lower baseplate (close to CG)
Hobbywing Skywalker Quattro 20A ESC board
GensAce 5500mAh Lipo (25C)

To Air is human , to trimix is divine
 

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