vosper,
There are two reasons to use two ESCs when running two motors. The first is that a single ESC isn't capable of handling the current requirements of both motors, so, you use two of them. The second reason is because you want to be able to control each motor individually. In the first case, yes, a 'Y' connector the same receiver port will work. It will mean that there won't be individual motor control though. Both going the same direction at the same speed. In the second case, no 'Y' connector. Each ESC going to a different receiver port, each being controled by a seperate channel/funtion.
The cable from the ESC to the receiver does two things, and some do three. Power is taken from the receiver to make the ESC work (not the motor, but the ESC). The signal from the receiver is sent to the ESC to tell it what it's supposed to be doing. And the third thing, if the ESC has a BEC, it that power from the motor's battery is sent to the receiver to power it, instead of a seperate reciever battery. The first two are common to all ESCs, the third thing is only for those ESCs that have a Battery Eliminator Circuit.
If your ESCs have the BEC then one of them has to be disabled. Otherwise you will have problems.
- 'Doc
There you go, more than you ever asked for.