[jcg1541]

I am having doubt about using attitude mode to do straight vertical diving. In my testing
when I hold the heli with my hand, straight downward position causes roll oscillation vibration, in
this video, at 0:37 mark and again at 0:52 mark,
<video removed due to private information involved>
.

It appears that attitude code loop is trying to find the gravity acceleration on the bottom (belly)
side of the heli , but the ground is pointed to by the nose when in straight downward dive. 
The attitude mode diving is only stable when I dive at 80 degrees.

[jcg1541]

OK, I just tried rate mode with the same exercise. Rate mode has not oscillation when nose points straight down.

[TheOtherCliff]

I can imagine that.  That doesn't help you much.

I can imagine it does that because with nose pointed straight down, then any direction of roll is as level as any other.  So it does not know where to put the roll axis.

From that I would think that if you tried to do more than 90 degrees of pitch, where the roll is actually upside down that it would try to roll out.  Imagine holding 180 degrees of pitch so it was perfectly upside down in pitch.  Then the roll would also think it was upside down even though the roll stick was neutral.  It would (I guess) try to roll back to upright.

I don't think this is related to gimbal lock, but it's possible.  It makes me wonder what INS13 would do in this case on Revo.

[jcg1541]

Thanks for confirmation.

I had a bliss with my first ever FPV flight today with this gearless setup with low P gain (36) and in
attitude mode.I didn't turn on the onboard DVR recording. So, no video recorded to share.  It was
so intense leading up to today's flight that I forgot to attach the FPV goggle's antenna and still
managed to fly it. The low P gain makes it very stable in open field, but the drift makes it unsuitable
for testing hover in office cubicles.

I figured out why FPV videos on youtube are always action packed. Today in my first FPV flight, I
instinctively had to do non-stop forward flight because the FPV video feed gave no perspective of
depth of the scene. The FPV pilot needs to continuously turning and moving to get the visual ques
to know where the craft is. It is the opposite of line-of-sight flying, where we stop all actions and
try to hover still when we lose track of the heli's movements.

I am still bewildered by what happened today. The feel of insecurity about what is on my sides
and what is behind the craft made me want to land the heli on a landing strip while in forward
flight to avoid "danger". I used to land the craft next to my parking spot in between the fence
and the trees, but now I landed it on the open grass. It was not planed. I didn't plan a landing
approach. But it was a safe touch down without a scratch.

[karla]

Yes  I can certainly relate to your fpv description.
I flew my first fpv with a heli that did not even have a flight controller, just a tail gyro.
It was exhilarating. So different from los flying.

[TheOtherCliff]

The first one is much harder than the second or third.    You quickly get used to seeing it from the air.  I hope your camera does well when looking into the sun, else it is all silhouette and you don't know how close the tree is.

My first FPV was fixed wing, but you would probably say that I cheated.  I used a laptop display and took off LOS.  It was still hard to do.  Fixed wing it is flying faster than a quad and will fly away sooner.  If you get lost FPV you will have a hard time looking up to find it.    After about a half a flight I got used to seeing things from the air.  Second flight I even landed FPV.

[jcg1541]

OK, Did my first rate flight today with a hard landing because I didn't realized that I could/should have switched to attitude mode for the landing approach.

Next is to book a flight to Las Vegas.

[jcg1541]

I have been struggling with rate mode tuning for 2 weeks. Whenever I fly rate mode toward some direction for
more than 2 seconds, there will always be a "rebound" to stop my action on track. CC3D seems to take on
a life of its own.

I still have not managed to dive straight down for more than 2 seconds.

[TheOtherCliff]

Just some thoughts:

You might try increasing pitch/roll PID "I" term.  Quads "blow out" (unstable pitch) at high speed if the "I" term is too low.

You could try speeding up / slowing down the main rotor to see if the problem happens later / sooner.  If so, it may be you are hitting the copter top speed.

Have you tried from a dead stop so that you know you are not flying faster than 20m/s after diving for 2 seconds?  Free fall is about 10m/s ... for 2 seconds is 20m/s.  Is it powerful enough (and you brave enough ) to fly horizontally at faster than 20m/s?  I bet it has the same problem when flying fast horizontally.

Rate mode is similar to unstabilized.  Can it be flown unstabilized to see if it is a copter issue or a FC issue?  If it always fails in pitch direction, maybe just set pitch to manual for a test??

[karla]

... Whenever I fly rate mode toward some direction for more than 2 seconds, there will always be a "rebound" to stop my action on track. CC3D seems to take on a life of its own.

John, can you please elaborate a bit what you mean here? What are you doing and what is happening with heli?
Rate is hardest to fly but still the most predictable stab mode, in my experience.
I think it will not be difficult to fly just with yaw set to axis lock and all others manual. To test what Cliff suggests.

[jcg1541]

Good suggestion. I will try the axis lock of the tail and manual cyclic with my gearless direct drive.

If anything goes wrong, I will just switch back to attitude mode to regain control.

I was too cocky today and didn't turn on the fpv recording for tracking flight path in case of lost direction. The geared setup flew too far. My brain froze and didn't switch back to attitude mode to regain control before I lost sight of it. It flew away. Lost somewhere in the snow. 250 dollars.

I will have a good story to tell the Dunkin Donut girl tomorrow. She is curious about my heli on my dash board when I drive throu for lunch every day. I put both the geared and gearless builds on the dash board and tape them down.

[jcg1541]

I tried both manual cyclic and high gain rate cyclic today. Both with tail axis lock.

Both gave me toilet bowl effect. But I don't know if it was pilot induced oscillation of if the gyro physics makes the wobble. Manual cyclic is unflyable . High gain rate cyclic is barely flyable when I try to counter the flushing action.

[jcg1541]

It should have been pilot induced oscillation. I had the roll stick with zero exponent but pitch stick with very large 75% exponent.

I was not aware of the situation until just now. No wonder it behaves so out of wack. When I try to correct roll, it is very sensitive, so when I try to correct the pitch it is unresponsive, so I force it hard, but then when I try to correct roll , I over correct it. Then I soften my finger, and the pitch becomes unresponsive, and go back to over correct roll, and then it just spirals. Roll is over corrected and pitch is under corrected. I have been flying like drunk for 2 weeks.

[karla]

You are talking about stick exponential settings of pitch and roll in the transmitter right?
If so, yes then I can imagine its difficult to fly, regardless of rate, attitude or PID settings of the FC.
Sorry about your fly-away. I have just gotten a pair of these TrackR bluetooth units I am trying out.

[jcg1541]

OK, Got my first rate mode "110" degree diving . Apologies for the protection film smudge.
The dive lasted 2.5 seconds. I was so tunnel-visioned on this dive, I flew it with the smudge on FPV,
totally unaware of the blurred feed,
.

I flew another round laid-back attitude mode after taking out the smudged film. And it was a beautiful day,
.