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T200 thrusters and side scan sonar interference?

Hello! I’ve been working on an autonomous sonar boat for the past few months. I’m trying to use the boat to map lakes and find targets to dive on with my ROV. I got the boat up and running very quickly with ardupilot Rover. However once I added the sonar I immediately ran into issues with interference in the sonar anytime the motors were running. I am now on my third motor configuration. I have tried two sets of no name Chinese branded brushless thruster motors. And I have now tried above water brushless motors connected to flex cables and spinning props under the water line. All of these configurations have produced interference in the sonar. I have done a large number of tests. I’m sure that the wiring is not the source for the interference. The sonar runs on its own battery with nothing else connected. My tests have shown that any thruster motors even without props generate noise when in the water with the transducer. In the case of the above water motors. It seems the props are generating noise thats still picked up by the transducer.

So my question now is. If I spend the money on a set of t200 thrusters which should be the highest quality of motors I will have tried. Will that cure the interference? Hoping someone else has had experience with side scan and these thrusters and can advise. Thank you!

Hi @Jonny360, welcome to the forum :slight_smile:

Sounds like an awesome project! :smiley:

This could be from:

  1. motors running or vibrating (themselves or some other part of the vessel) at a frequency similar to the transducer frequency, causing measurement noise (fixed by using a different transducer, different motor speed, or different motors)
  2. motor power or control wires running close to the sonar or its cables, causing electronic signal or communication noise (fixed by better electrical isolation between the sonar and surrounding electronics - separate power supply is a good start here, but can also be good to physically keep the motors and motor cables away from the sonar and sonar cables, and/or reduce electrical leakage by encasing or wrapping noisy and/or sensitive wires or components in metal)
  3. the thrusters creating bubbles around the sonar and blocking the outbound or return path of the sound, causing measurement degradation (fixed by changing thruster placement relative to the sonar, or using a different propulsion mechanism (e.g. towing the sonar setup from a separate vessel, or using something biomimetic (copy fish movements), piston-based, or paddle-wheel or oar based for surface vessels))

Very hard to say without knowing more details of your current motors, your wiring setup, how you’re controlling the vessel (at least with respect to motor speeds), and your sonar’s transducer frequency. If you want to/are able to provide more information then we can perhaps give a clearer response. In the meantime I’d direct you to our T200 technical details, where you can find the relevant thrust output and operating frequencies (RPM) for a given supply voltage and control input value.

Thanks for your reply. As I mentioned i’ve done extensive testing. It appears that the cheap chinese brushless thrusters were causing emi through the water to the transducer. With no props on dipping the motors in and out of the water at low throttle would cause the interference to appear and disappear. This is obviously not a vibration or bubble issue. Likewise not a wiring issue.

The humminbird helix 7 mega si unit I have uses 455khz and 1.2mhz. I run TBS crossfire to a Matek f405 wing flight controller running ardurover.

I expect it is electrical noise from the motor controllers which gets into the water and capacitively couples to the SS transducers. I would suggest “grounding the water” with respect to the sonar - so expose the sonar ground to the water.

In the case of the current configuration where the brushless motors are above the water, how would the esc noise get into the water?

If the noise is greater with the motors in the water vs not in the water, then I expect grounding the water will help. If there is still noise when the motors are out of the water then perhaps you have more than one noise source. In both scenarios the noise is likely electrical and not acoustic.