I purchased a gimbal protector bracket (not a lock) on Amazon for my P4. I finally had a chance to fly it today and I was tripping out how weird the bird was acting. It would not hold a hover (more than the usual problem) and when I descended from a high altitude with full left stick down it would barely descend, took forever. I figured the bracket was interfering with the downward sensors so I took it off and flew again. Everything was back to normal. I contacted the seller with my concerns and he responded with a picture showing EXACTLY where the bracket had to be positioned (4.5 cm from the front of the landing gear). I have yet to try fly again but I am pretty sure that is where I had it originally. I may have to measure exactly (1.77 inches) and make a mark on the gear so I know where to place it. Not sure if it is worth it... Just posting this as a heads up in case anyone else has problems.