Also got a bit deeper understanding of the problem with the turn overs, its not really doing it in flight, it does it when you land or touch the ground. unless you put it down really soft it will throttle up for a millisecond and eather flip or just go straight up, you can hear the motors reving up pretty high for a fraction of a second....its really strange..
Lemme ask this first because it's critical and can affect *all* aspects of FC-controlled flight *after* the launch. When you start up the motors do you let it sit there for a bit at very low RPMs -or- do you immediately rev up to about half throttle to get away from the ground? That second 'or' part of that sentence is the correct way to launch.
Whyzzat? By design the FC's purpose and intent is to fly in free air. If the aircraft bobbles a bit and the landing gear touch the ground back and forth the FC gets 'confused' because it's not free air it's pushing against it's solid ground, so later flight in free air it behaves differently. It blasts the motors as -if- it's pushing against hard ground, which is too much throttle.
About the landing rebound, imagine driving a car.... As you slow the car to a stop, if you hold the -same- brake pressure continuously until the car stops, when it does finally stop there's a slight bounce backwards. The suspension leans forward against the friction of the tires. Energy is stored in the compressed suspension. As long as there's forward motion, slowing down, inertia leans the car forward. When motion stops the suspension is still leaning forward. THAT STORED ENERGY MUST BE RELEASED, which it does by rocking the car backwards. The only way to stop a car -without- that rocking motion is to gradually decrease brake pressure as the car speed drops. If brake pressure drops to zero just as forward speed drops to zero there's no stored energy in the suspension (or at least none that's noticeable) and the car doesn't rock back/forward. It's a real skill to learn how to drop the throttle on the quad to zero just as altitude reaches zero but I've managed a few letter-perfect landings once in a while. Rocking a car a bit when stopping is as normal as is a slight bounce when landing. But.... that's why I asked that first Q about the launch, related to the large RPMs and even flips that you mentioned, because once the FC is confused and disoriented at launch time all bets are off for the rest of the flight including the landing.