I am trying to configure my Bix3 with a pixhawk, and I have found a very strange problem.
I have 4x 9gram metal gear servos for ailerons, rudder and elevator, and 2x 9g plastic gear serovs for flaps.
Problem is that if all these servos are connected to the Pixhawk and I switch into FBWA, alle servos lock up and go start pulling all that they can in one direction. If I disconnect the ailerons and connect the flaps servos to the aileron channel everything works great. If I disconnect the rudder and elevator, the flaps and ailerons work great. In conclusion, I have found that by having 4x metal gear servos and 2x plastic gear servos the issue is provoked. By connecting only one of the aileron servos (either one, doesn't matter), there is no problem. By changing one of the aileron servos to a plastic gear servo, the problem is reduced. By that I mean that the servos don't lock up permanently, just for a second or two.
When the servos do lock up, I can free them back to normal by unplugging the aileron servos, i.e. reducing the number of servos connected to the Pixhawk.
I have found that the FBWA nature of using all the servos at the same time is the problem causer, in MANUAL I can operate all the servos just fine. A little strange, but in MANUAL I can use all the servos simultaneously, but if I but both sticks of the radio to a corner and release them so that they bounce back to center really quick the problem occurs and the servos lock up to max again.
The metal gear servos are 9g Turnigy TGY-50090M and the plastic gear servos are 9g HobbyKing HXT900. The servos rail is powered by a Pololu 5v 2.5A step-down regulator (D245V22F4), which is connected directly to the output of a 3DR power module in parallel with the ESC. Link to the power module is attached below.
My conclusion is that the system is somehow overloaded or influenced in some way by the metal gear servos. As i said, by using plastic gear servos on the ailerons there is no problem.