water proofing 12 volt electric motors

[ben gosen]

i am building an rov using bilge pump motors. i’m wanting to go up to 60 mtrs i have heard of filling the motors with oil but have been told that that wiil cut doun the efficiancy of the motor combine that with 60mtrs of tether and i will have little power to play with. i have oversized the motor to try to compensate. but i wonder if there is another way of water proofing the motor.

[Andy Shiers]

Alot of manufacturers in the eighties went the cheap and simplistic route using Brush motors , For example ………… Phantoms or Sprints. If size is not a problem use 220v and magnetic coupling.
The real big problem Phantoms had were water ingress through the 1/4 orifice ( Shaft ) due to fishing line getting trapped and bending causing friction on the 108 orings , 117 orings Inner and outer nylon bearings and the oil leaking out , This then caused the Water to flood into the ROV completely as there were no water blocks in the tubes , well …… apart from the lateral thruster which I and my brother enclosed in a bit of shit pipe and kept serperate !
The sprints problem with the thrusters was dust build up on the armature causing noise on the video or Thruster heating up and failure. ( But as long as the Thrusters were "blown-out" periodically as in maintenance there were no problems . 🙂
You say you have little power to play with , What power are we talking about ?

[ben gosen]

thanks for your reply. i will be using a deep cycle 12 volt marine battery with four1000 gal/hr bilge pumps

[Andy Shiers]

Hmmmm 😕
Have you looked into Benthos , how they utilise their thrusters ?
Mini Rovers that is 8)

[ROVRatt]

The power issue at 12V will be the length and thickness of tether. To deliver 10 Amps at 12V on a 10 metre tether will require conductors the thickness of car battery cables or thicker. To decrease the size of the conductors you need to up the voltage. This is why work class ROV’s typically use 2000 – 3000V to run their electrics through thin (relatively) tethers. These are the laws of physics and they are inviolate.

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