Quadcopter crash in stable mode, ver 1.7..

[oterpoter]

Hello people!
Today I was playing with my quadframe quadrocopter with Multiwii 1.7 board from quadframe.com.
This has been behaving perfect, but today I encountered somethibg VERY strange.
I was flying in some light wind today, and I gave almost full throttle, then dropped throttle letting it fall, and a new burst. When I then dropped throttle and gave another burst, it wobbled and then went into a spin that just got faster and faster and it then plummited to the ground..
Outch...
Was this the Autolevel going crazy because it started spinning? Is this a problem other ppl have encountered?
When I give it a burst after it falls it is unstable so the sudden burst might be a NoNo to do?
I am building a octocopter for heavy lifts now. All DXF drawing for the whole thing, frame, landingskids and 2-axis gimbal is getting CNC'd any day now!

[mr.rc-cam]

If MINTHROTTLE (see config.h) is too low then it is possible to have this problem if you chop the throttle too low during flight. If the motor speed becomes too low there may be a delay before it can achieve reliable speed again.

FWIW, I've found that the throttle jamming trick is a bit risky. As cool as it looks, I crashed doing it (and I won't be doing it again). While in flight, throwing the stick to minimum and then quickly back to maximum was too much stress, which caused a prop to break a blade. It was sort of like a mid-flight explosion: Within a heartbeat the prop's remaining half blade shook the model like a rag doll, ripped out the motor, and the quad spun hard into the ground. So your mileage may vary.

- Thomas

[oterpoter]

spot on! thats what happened to me.
Also I have altered the code so that when throttle = 0, the props stop completely..
This is Not smart, becuase I experienced the same thing.
It just went into an spinning backflip from hell, and smack down to earth.
fortunately I was not that high up, and the damage was minimal
It is already back in business...!!

[mr.rc-cam]

Also I have altered the code so that when throttle = 0, the props stop completely..

That explains it. The FAQ has good information why stopping the props is not recommended and your experience reflects it's fatherly advice.

[copterrichie]

Yeap, I had to learn this one the HARD way myself. There is no other way to fly but with the MINTHROTTLE set above the point where the motor will spin and using the MOTOR_STOP feature. That happens to be 1150 for me but I am strongly considering setting that to 1200 or 1250 now.

[oterpoter]

Today I was taking my quadrocopter with FC from quadframe.com. I have not been flying since it crashed last year due to wintertime in Norway. In addition I have encountered some strange wobbel/oscillation on indoor tests. Every second it did a small wobble/nudge, hence it seemed to me like something was wrong. I have changed the motor that appeared to acting strange (back right motor), and today I was taking it for a spin.
I was not able to disarm the motors using left-yaw, throttle-down, but arming them worked.
I was flying in stable mode just hoowering close to me, when it all of a sudden again went into a spin, like a left sideways flip.. With a destructive crash of course!!
Luckily I was only 1.5m up in the air, and it was dead steady before it just flipped..
The same quad did a similar loopflip which ended in a crash as mentioned earlier in this thread, but then I had done the mistake of letting motors come to a complete stop with throttle all the way down.
This is not the case now, so WHY did this happen? Is the Fc to blame? Just before I went flying i calibrated it using MultiWii v1.7 software, and every value looked correct! Throttlerange was ok, as was all the other values...
I had been flying 3-4 minutes only when this happened, with no indication before it just went crazy..
Any suggestion is most appreciated.. I do not want this to happen again...
Regards
Mathias

[kos]

can be wire or a deffective connetors .. when crash happens ..

[oterpoter]

No defect connectors/wires.. Plugged in battery after crash.. Everything fires right up...

[mr.rc-cam]

No defect connectors/wires.. Plugged in battery after crash.. Everything fires right up...

That doesn't mean your wiring is reliable. Intermittent connectors/wiring can make common troubleshooting very difficult. I experienced this first hand, as discussed here:
viewtopic.php?f=13&t=1307&p=10079&hilit=bullet#p10079

That link goes to a discussion about my bad bullet connectors. But there are plenty of other connectors and soldered connections that can cause grief. So your troubleshooting should be prepared to expect anything and everything.

- Thomas