I have a 370 quad with a naza mv2 and i just build a 640 size with the pixhawk. the 640/pixhawk seems to be very sluggish when responding to commands, meaning if I input some pitch and then stop, the drone will keep moving forward. trying to understand if it is because of the size and my setup/configuration. I am running 3.3.3 and 15inch prop
Its most likely due to your PI gain settings. Depending on the size of your quad these parameters need to be changed as they are a constant feedback into your system for correcting those sluggish movements and setting how twitchy you want your system to be. These parameters can be changed in mission planner and is very much a trial and error method to getting the right values for your personal quad unless you know how to calculate them by hand.
thank you. I will check them out.
but your theory on the quad having a lot more inertia is completely correct. This PI Gain settings are just numbers to which to feed into the motors to counter a change in direction. so therefore they need to personalised to your quad