Thanks for giving me the chance to join this community. I have recently built a 450 quadcopter with an APM 3.1 mini FC, FSi6 radio, simonk 30A ESCs and sunnysky 980kv motors. I have recently received a 433mhz 3DR radio telemetry and since then I have been having some issues.
The radio link works well. I can see the data sent from the quad and I can also send commands from mission planner.
However, whenever the 3DR is plugged in, the motors have short speed changes as if the pwm values jumped and then back to where they were. Initially, I though this could be some errors received from the link so I disconnected the TX and RX wires from the 3DR to the APM and the problem still there. So it looks like the problem could be coming from the ground of the 3DR (kind of a noise), but I don't have and oscilloscope to see whats happening. I also tried running a cable from the GND of the 3DR to the GND of the ESCs (which is technically the same), just to prove that it was not a ground issue and it did not work.
So it looks like the APM does not like the 3DR(even without the TX and RX wires, just GND and +5v) and this causes changes on the motors.
I really do not understand what's going on and I would appreciate it if someone has come across something like this and can give me a hand