Underwater DPV Motor Selection

Not exactly the same as a hydro foil but a lot of the same concepts go into both. I’m looking into building a Diver Propulsion Vehicle (DPV) to pull me around while I scuba.

Having a hard time picking a motor. Too many options! LOL This motor will be in a waterproof housing and drive a propeller shaft through a mechanical shaft seal.

What are your suggestions on a good motor for this? It doesn’t need to be fast. Just strong enough to pull at 2 knots (or so) and with a decent battery configuration, last 4 hours.

Thanks for any support!

Been doing more and more research, I think I’m going to try a 6374 motor. 180-190kv

More of a general motor Question. How is heat build with these?

Figuring there must be some build up, especially if my design will have this encased in a waterproof tube.

What are people’s thoughts on the motor choice?

If you’re going to use an outrunner, you’re better off running it wet, so it will take care of the heat issue.
you might also want to use a lower KV, lower speed propeller are more efficient… and as you hands will be close, less dangerous :slight_smile:

Thanks Matt,

Do you have any recommended KV?

I have no experience with what you’re trying to do, but i guess as low as you can get would be better as you don’t need speed, but torque instead.

With running an outrunner ‘wet’ would it have corrosion issues with salt water? Do innrunners run ‘cooler’?

I could gear it down as well.

Thanks for your help!

I’m running mine in salt water for a year and no corrosion issue, I replaced the bearings with stainless ones and the shaft with a titanium one.
Main issue is that there are losses when running it wet, and they go up exponentially with speed.

I didn’t use an in-runner so i can’t say, but that usually mean using a gearbox, and making sure it’s waterproof :slight_smile:

Yeah, my design originally planned for an inrunner. The batteries and everything else will need to be waterproofed, so was planning for that already.

Knowing that it wont corrode makes me more optimistic.

Had the same application idea and really interested in this project. Any update ?
Have been reading a lot on this forum and would advice a c80100 130kv or 80kv at 12S with a stock Yamaha or even a down scaled Mercury propeller. All the stl files are available on the forums on various posts.

You might want to use a duct sinds sea scooter basically don’t need speed but thrust. If you are going speed, you’ll better go higher Kv for jet impeller like the Seabob

Thanks! No updates yet. Just lots of research. I see some people using inrunner trike motors. Definitely want a duct, not only for better thrust but also manhood protection :joy:

I’m personally going for long run time, min speed (1-2 mph)

I’ve been reading about inrunners too, but they usually use a reduction gearbox to get the needed torque.

Typical sea scooter use 300W brushed motor with gear reduction to travel at 2-3 mph. Got me thinking if we really need more than 1kw brushless motor for this application ? :thinking:

The few builds I’ve researched that have website:

both use inrunners. one uses a 50 dollar e-trike motor and the other uses a golf cart motor.

That was worth reading, thanks for those infos !

I wish they would have tested them and shared the result :slightly_frowning_face:

The first one still use a gearbox to get a decent torque :slight_smile: The second one may nod need it with this diameter of rotor / stator…

Stats would be great! Lol. I agree. Running the numbers the second one doesn’t get more than 30-40 min run time.

You need 6384 with 120kv,
It’s strong enough for Divers and running cool.

Greetings frank

Thanks @JetboardCologne didn’t even notice i got a reply :grin:

can’t find many 7x5 props. Any recommended links?

Take a look here : Seabob reference - Props & Ducts - FOIL.zone

Even the Seabob seems to use an outrunner (maybe in oil) for high torque and speed. They are using a 50kv (2500 rpm/50V) motor rated up to 4.5kW for their top model which is worth $15k.

120kv seems to be pretty high for this application… I would go for something in the 70kv range with 12S battery. APS C80100 80kV would be a good fit. Plenty of torque and you still have some power margin to experiment.

120kv is good, you need max 8s lipo and have more place for capacität.
Best regards Frank

@Sliman_O do you know the run time on the seabob? how many aH that thing use? Must weigh a ton lol