A couple of days ago "Chugalone100" asked, "In a twin-motor arrangement, is a throttle mixer required to properly coordinate differential thrust control, or can this be managed directly through transmitter programming?"

For many years the connection between the radio receiver and the servo, or motor controller has had three wires, these are conventionally coloured black for the 0 volts line, red for the nominally 5v line and white for the pulse.

This is the way my torpedo boat destroyer is configured. The white wires for the two 'up-down' sticks are connected to a single pole double throw microswitch, one channel to the normally closed contact and the other to the normally open contact. The common is connected to the starboard motor controller, the left stick is also connected to the port motor controller. A servo connected to any other channel operates the microswitch. So in one position of the microswitch the motor controls are connected and both motors are controlled by the left stick. In the other servo position the two motors operate independently. The rudder is operated conventionally by the right stick left-right. The two extra proportional channels on my FlySky FS-I6 rotate the forward gun and the torpedo tubes.

My USS Melvin (Lindberg kit) has a different system. Up-down on the left stick controls the power to both motors, left-right on the left stick controls the balance between them. So I stop both motors and put the stick over one motor will run ahead and the other astern. The motor control is a home designed and home built job. I built the USS Melvin in 1979 when I was home on leave from the British Merchant Navy. Since the only fault has been a failure of one power transistor.

I normally run the USS Melvin on my 4 channel Futaba transmitter but sometimes on either of my 6 channel Futaba transmitters.

There are other ways of doing it.

Thanks for the compliment!

The model is a "C" class destroyer (also called 'Star" class) they were built by Palmers on Tyneside in north east England in 1897-8. It is 3 feet long and built 'bread and butter' from 1/2 balsa and sheathed with fine glass fibre and polyester resin.

The superstructure is various thicknesses of EverGreen styrene sheets.

The conning tower and forward gun platform are aluminium alloy as are the guns, anchor davits and mushroom vents. I used my Toyo ML 210 lathe to make those.

Thee funnels and vents were 3D printed by the local library from STL files that I made. I have since bought a 3D printer.

I still have to make the torpedo davits, anchors and the ship's boats.

The photo of it sailing on Lake Mendota (about 100 miles west of Chicago) was taken on my wife's phone. When the lake thaws and I get out sailing again I'll get some better shots of it.

My recommendation is to use two motor controllers. If you have enough channels on your radio then it's easy to have one channel select control, independent or not.
I run my torpedo boat destroyer on a FlySky FS-i6 and use the left throttle to control the port motor and the right to control the starboard motor, if the left switch is in the down position both motor are controlled by the left stick. When I am bringing the model into shore I run independent, when the model is in the middle of the lake I run them combined.

The last picture is of the Aerokit's RAF crash tender. I built one of those in 1968-9.
Edit a few hours after the post, the last picture has now been removed.