The more I think about this I think there is a flaw in my plan. To use the continous rotation servo, the elevation stick needs to operate up and down, but with the rx18 the only option is to have output to a motor that runs the barrel up and down continously with the stick pushed one directin,no independant up or down, just continous movement, moving the stick the other way fires the gun.
This will be a neat challange to see if I can manipulate the stuff to make it work on 4 channels. I know i can make it work easy on 5, using the landing gear ch5 on a momentary button connected to the barc main gun, and the elevation stick independant on its own servo not going through the barc or rx18.