Grounding Motors and Arduino/ Motor Noise Concerns

Hello all, I am working with a team on designing and building an ROV as a senior design project. This site has been extremely helpful in guiding this project since we are a team of only Mechanical Engineers with little electronics exposure.

The design will use two Arduino Megas, one on surface and one onboard the ROV for control . The motors will be driven using Pololu motor drivers. The motors have a stall current of 11.7 amps at 19V and only 4 of the six thrusters will be powered at the same time.

The tether will be 50' long with 12 gauge wire for powering the thrusters, 2 twisted pairs for full bridge RS 485 communication, and 2 twisted pairs of an ethernet line for power to the Arduino.

The 6 motors and the Arduino on board the ROV will be connected to the same ground rail (aluminum frame of the ROV) which will be connected to the ground of the power supply via a 50' long 12 gauge wire.

The power source for the Motors will be a AC--->DC convertor and the power source for the Arduionos will be a bank of AA batteries outputting 10.5 V (this battery pack will be on surface so power must be ran down the 50' ethernet line)

NOTE: The maximum steady state current draw of the system should be less than 20 amps

Should I anticipate motor noise on the ground line to be a problem with this set up? Will using the aluminum frame of the ROV as a ground rail have any negative effects? Any other concerns that I am over looking?

Here is a simple diagram, any grounding suggestions/concerns?

You've got the most important thing right, which is that the Arduino grounds and power grounds are connected at just one point, at the rover. As long as you don't connect the surface Arduino to a PC via the USB port (which would join the grounds at the surface end too, if the motor power supply has the negative side connected to mains ground), then you should be OK.

To reduce motor switching current in the tether, I suggest connecting large decoupling capacitors across the motor supply at the rover end (the Pololu controllers may already have these), and an inductor in series with the motor +ve supply between these capacitors and the tether. You can make the inductor yourself by winding a few turns of wire through a fairly large ferrite toroid.

Hi
in addition to dc42 comments,would it not be a bad idea to twist the power wires to the thrusters, say one turn per foot or so..(helps to reduced radiated noise).
If you have a choice in motors my guess is that brush less motors would be better to help reduce noise both induced and radiated..Maybe a motor expert may be able to guide you as I am not an expert here.
goodluck in your project.
jolphil