Did you use these wiki instructions to setup your pitch and roll gimbals: copter.ardupilot.com/wiki/camera-mount/
Here is the layout of the PX4 IO board: plane.ardupilot.com/wiki/common-px4io-overview/
You should be using the USART2 connector at the end of the board away from the servo end. The connector is numbered 1 - 5 starting with pin 1 on the connector edge closest to the edge of the pwb. You should be using pins 2,3, and 5 (gnd).
Hope this helps.
You need to have a common return between the PX4 and the servos. If you are using the BEC to power the servos and the PX4, then you have a common ground between the servos and the PX4 through the BEC.
However, since you are probably using the PX4 with the IO module, you are powering the PX4 with the IO power module.
If you are using the same battery to power both the PX4 power module and the BEC, which is powering the servos, then you have a common ground through the battery.
If you are using two different batteries, one to power the PX4 and the other to power the BEC, then you will have to make sure that you establish a common ground through pin 5 on the USART2 connector with the servos negative (black) wires since the BEC is powering the servos and not the PX4.
TCIII ArduRover2 Developer
You cant really complain for the price it comes in.
However after setting up everything, you realize that all of the wiring does cause a huge headache as it interferes with the PX4’s mag compass.
Seriously makes you consider buying the TeamBlacksheep’s frames. Especially the Discovery Pro.
I just spliced the ground wires for both the servos together. Had the signal pins go to the correct output.
And provided power from the ESC signal output area pins. The middle row of pins. I hope you understand what i am saying. If you don’t, tell me i will try to make a video and post up on youtube.