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KK2.0 Quad Tuning Questions and odd behavior

#1
Hi everyone, I am new to the forums but I have been watching flitetest for a long time, and have now finally finished my first quad.

I flew it several times over this past weekend and found some odd behaviours.

1. When I go into fast forward flight and then try to slow down, the quad pitches back violently, kind of like its trying to brake as hard as it can. It's not terrible because it does stop the quad, but Id rather not have it since I don't give it the stick input to do that and it means I have to increase throttle every time it happens so it doesn't fall out of the sky. Any idea why this is happening?

2. I seem to be stable most of the time (P gain = 80, P limit = 100, I gain = 5, I limit = 15), but occasionally it will twitch unexpectedly, like one side will drop fast but then recover. This happens more in wind, which is to be expected, but Id like it to not happen in zero wind conditions. Any idea what could be causing this?

Just some basic info about my set up: 2 x 5000mah 15c Zippy's, 4 x Park480 850kv, 13x4 APC thin electric, 4 x 600 size carbon tail booms for arms (motors are about halfway along the boom to protect props, Id say 800mm from motor to motor)

Any advice is welcome! Thanks.
 

Tritium

Amateur Extra Class K5TWM
#2
The only way a quad can slow down is to reverse the thrust. This is what you describe. There is no other way to transition from fast flight to a stop but for the quad to tilt and apply "braking thrust".

Thurmond
 
#3
I understand that its necessary to pitch backwards to slow down, the only problem is that I don't tell the quad to pitch back. It just does it, and quite hard too. it goes from about 15 degrees from level in forward flight (Elevator on the radio is pressed forwards slightly) , to 75 degrees from level in the opposite direction (Elevator on the radio is centered).
 

Tritium

Amateur Extra Class K5TWM
#4
Are you are trying to slow down by lowering throttle only? You need to use a combination of back stick and throttle lowering. If you drop throttle only, then the behavior you describe is the result of the programming of your controller doing the only thing it can to slow the craft which is pitching backwards enough to counteract the forward momentum.

Thurmond
 
#5
No, the throttle is unchanged when this happens. Does the kk2.0 board actually have any knowledge of the air speed of the quad copter? I have auto-level off and my understanding was that it only knows the rotational speed of the quad. Meaning a centred elevator would cause zero pitch change. In this case that would mean the quad should remain at its current attitude, not pitch back.
 

Tritium

Amateur Extra Class K5TWM
#6
Ok you don't lower the throttle and you don't pull back on the stick so HOW are you going from fast to slow? :confused:

Thurmond
 
#7
I pull back on the stick briefly, to get it back to level, but then it continues to pitch back to around 75 degrees even though the stick is centered. It almost seems like the props are acting like wings and catching the air..

I actually had a small crash yesterday when this happened, when it pitched back sharply after a fast forward flight one of the propellers flew off! Luckily it was only a foot off the ground and I was pretty far away, but that is definitely a problem. Any ideas on how to better secure collet style prop adapters??
 

Quinchu

Junior Member
#8
I had the same problem when flying with the safe-level on. If you keep safe level off then it won't try and compensate when you stop quickly. Much harder to fly, but a lot more fun when you get use to it!
 

Quinchu

Junior Member
#10
I've been using the 1.2FW on the Kk2 board and I found that if you lower the self level settings then it won't pitch as hard, but as the others said you need to lower your throttle and pull back slightly. Another point to make about the KK2 board is that if you have any sort of stick scaling in excess of what the stock settings are then you're going to get those violent pull backs.

That being said, if you want better transitions then you might want to add some Expo and DR on your transmitter. This way when you pull back a bit then it won't affect the quad as much.
 
#11
Thanks for the advice, I tried messing with some of the PI settings but no matter what I did it still does it, seems like ti might just be a characteristic of my quad.. Also just to clarify I am not using self level at all yet.

I have another odd behaviour now though that I was wondering if anyone else has seen. When I try to yaw to the right, the front right of my quad drops very fast almost as if the motor loses power. When I stop yawing it recovers, but this makes it very very hard to fly. I checked and the motors are speeding up correctly (back left and front right speed up to yaw to the right). Any one have any idea what could be causing this? Is it a kk board thing or is my motor starting to fail?