Computer Fans

[AHarris]

This is probably a really bad idea, but considering my little knowledge in the actual construction of computers and considering I have never actually built a fully functioning ROV yet, I may be suggesting something that to some more experienced people is a completely idiotic idea.

I was wondering whether a computer fan could make a decent thruster as opposed to the considerably more expensive bilge pumps. Considering a computer fan costs about £2 ($4) it would certainly make a more ecenomical sense. I also believe they require less power and spin a lot faster, the only current issue I see is it not outputing enough power and it not being waterproof.
If it is a brushless motor computer fan then it can be used underwater can't it?

Do you think such a thing would work?
Pre-made housing, prop is already attached, it is a lot cheaper and a lot easier to mount as it has pre-fabricated screw fittings.


Update:
Someone has an oil filled computer case and it still has a computer fan, and it creates current! So this means it should be able to spin underwater but pressure may still be an issue? What do you guys think of a fibre glass PC fan?

[steve918]

It might work for a featherweight design, otherwise I think your going to suffer from a serious lack of torque.

[AHarris]

Hmmmm, good point.
Could always make the entire thing out of computer fans? Or is that just an overkill solution to the problem?

[derelicte]

computer fans are brushless and have brushless controllers built into them. I'd be worried that the electronics wouldn't like being submerged in water. the bearings could also be an issue.

stick one in a tank of water and see how well it works!

[AHarris]

I thought brushless where the ones which could be submerged?

[AHarris]

I think it shall be rather simple to wax seal the PCB as that remains in the case and is surrounded by plastic (so almost like filling in the gaps).
As for running the motor, apparantly what causes it to fail if submerged is the parts corroding after use and it not being cleaned out.
As I am running my ROV in salt water I shall be washing down everything and rubbing down the seals to clear anyway, do you think it will work?


Update:
Kinda thinking this through as I go along, shorting out may be an issue. A friend who has built his own, high end gaming PC and is also really good at computers anyway states that most computer fans are roughly waterproof anyway. If I oil fill it then double seal around the edges it should work... going to try it... I am still talking and thinking... ignore the rambling on.

[derelicte]

motors can be submerged, not the controllers.

[AHarris]

Ok, so if I wax seal the controllers then it should be fine?

[thegadgetguy]

Yea, you should be.

I saw somebody do this once before, although they actually used a magnetic coupling. It might work, but I am also of the opinion of steve918 that you will have a serious lack of toruqe.

[PSCG]

I have tested computer fans as thrusters (i have a lot of them) and the results are promising: No water was found at the fan's electronic control board or in the bearings, it spins as fast as in the air (but draws more current) and had enough thrust for the fan to escape my hands and spill water all over the place. Still, i don't know what type of fan would be ideal as a ROV thruster but i'll do more tests and post the results.