Okay, that makes things a little more clear. Now I have a couple more questions for you so we can narrow this down a bit more:
1) Does the rudder work when you try to turn it with the transmitter?
2) Have you tried swapping the speed controller and rudder servo connectors on the receiver?
3) Have you tried to spin the prop shaft by hand(with the batteries not installed for safety)
These questions will harrow down where we need to look next:
- If the rudder doesn't turn, that says it's a receiver issue and you will need to try to rebind the receiver to the transmitter. This should be explained in the instruction book(s) that came with the boat. If it won't rebind, you may need to replace the receiver.
- If the rudder does turn, swapping the connectors will verify both channels work in the radio system and will rule out a radio problem and will tell us it's a speed controller or motor issue.
- Question 3 is to verify the motor and bearings are still in good shape. If the shaft spins easily, resetting or replacing the speed controller should take care of the problem if the radio is working properly. If you feel drag, that means either the drive shaft needs to be greased or the motor has corrosion building up inside. Removing and greasing the drive shaft would be advisable anyway as it's part of the basic maintenance required by R/C boats. I personally use a lithium based white grease on my boat's drive shaft
For the record, this is my boat:
