Sorry I was busy trying to get the ROV built before leaving for the beach this past Friday, and did not put the time in to update this thread.
The wiring for the control the system is pictured here. I am using an Arduino nano as the microcontroller. To have the Wii Nunchuk and video monitor detachable, I am using balance connectors. I also have a switch to reset the Arduino in case any wrong behavior occurs and I need to stop the motors. To monitor the behavior of the motors, I am using 3 LEDs whos brightness will correspond to the motor speed. If the LEDs don't match my control input, then I know something is wrong and I can reset the Arduino.
Here we are with everything wired up to the back of the circuit board the Arduino is mounted on. The tether is just a 50 ft ethernet cable. It's a cost effective method to get 6 wires in a nicely protected bundle.
Here are all the control electronics in the housing I made for them. On the bottom are the reset button, LEDs, and balance connectors. The top has a lid that still gives access to the Arduino usb for programming. The housing is round because it is made to fit inside a spool that used to hold 3D printing filament. Now that spool is perfect for winding the tether on.
The other end of the tether connects to six pins. These are the pins that will connect to the ROV body. It was a tight solder job, but actually was easier than expected.
And here are the pins with the mounting clip attached. Bolts will go through the holes on either side and bolt on to the ROV body. I also put silicone as a relief at the point where the tether exits the plastic. I also printed a TPU gasket to go between this plastic and the body.
I'll have to get some more pictures of the painted body with motors installed, as well as my tether spool. Right now it is going to be several days of leak testing (already found some!) and patching.