Originally Posted by ganobile
I was reading the R921X manual. There are a data/binding port. Can I connect a Aux Batt on this port? If yes I can free the channel aux4 and I can mix the aileron with this channel.
You can connect a battery to any of the ports on that receiver. They all share the same Buss. You can connect a Y Harness to any servo port and connect a battery to one side and the servo to the other.
I don't have the R921 in front of me, but I believe it has a separate Bind/Bat port and a separate Data Port. You can connect a Y Harness to the Bind/Bat port so you can connect a battery to one side and Bind through the other side. You can connect a Y Harness to the Data Port and connect a battery to one side and a Flight Logger or Telemetry Module to the other side.
I had a situation where I needed to use a Voltage Regulator for the Rx battery. It was connected between the Switch Harness and the Rx. I could no longer Bind through the Switch Harness Charge Jack so I needed to connect a Y Harness to the Bat/Bind port.
These are the only situations where I use a Y Harness in larger aircraft.