Thruster build

[DavidF]

Well i got some stuff in the mail the other day for my thruster build, 3 550 motors and a propeller. I probably screwed up with my choice of propellers, i thought it was a little different when I saw it online, but after seeing it in person I dont think its what im looking for. the other problem is that the shaft is a little too loose in a .125" reamed hole so I am going to order a .001" under reamer and try it. If that doent work then ill make it up as a collet type coupling (time consuming to make it that way though). These thrusters will be a sealed design and should hit 500' with out issues. Ill post more as I get things done. Anyway here is a pic of the 550 motors and a 540 motor from an r/c car for size comparison.

[bikerbones1968]

Cool looking props. You should do some wet testing when you get the prop adapters done to see what kind of thrust they will produce.

[DavidF]

Good Idea! I think Ill do that. Id really like to be able to measure the rpm's too so I can get a better idea of the sealing ill get. The seal im using has been used on a small water pump under 1500 psi and 1500 rpms but is likely to be less as the rpms increase. Im still working out a couple of items but ill post the cad images once I get it all figure out.... Need an amp meter too.... Im open to suggestions for testing them out so throw some ideas and your experence this way.

[darrenervine]

Motors look pretty sweet...prop does look a little too beefy from my perspective but I am no expert.
I am interested in the sealed housing they will be in...

Got drawings/pictures/thoughts?

Building one from scratch too and trying to determine best thrust options...

Thanks
Darren

[DavidF]

I'm working on the Cad drawings now, but it will probably be out of most peoples capabilities to build unless they have a home machine shop.

[darrenervine]

If you were starting from scratch and doing it all over again, would you use converted bilges or electric motors on your first build?

Thanks
Darren

[DavidF]

Honestly if money wasnt an issue id go with micro hydraulic motors, but I cant afford to do that... With out doing testing on the different motors its really hard to say what is better. I do like the brushless motors for the fact you can run them wet, and the bilge pumps for thier simplisity but they both have thier down falls. If the bilge pump motors get water in them they are pretty much a throw away, the brushless motors have to be dried cleaned and oiled every time and I would think thier life expectancy to be short.
By building an actual sealed thruster the motors would run dry and hopefully last without alot of maintence, and the assembly would be rebuildable and motors replaceable. The motors im going to try out are only 3.50 each, but the seal to make it water tight is 20.00 plus the time and materials to make the housings make them somewhat expensive, or very expensive if you have to pay someone to make them.
If you build your rov as a modular design then the trusters could be replace with different styles and types of thrusters so it would be no big deal to use a bilge pump fitted with a propeller or the brushless motors and just upgrade them later on if you needed to or wanted to. something else to keep in mind is how are you going to controll the thrusters? ESC or relays? with relays you would either use the bilge pumps or the brushed motors, and with the brushless you would have to use the esc's.
While looking thru my boxes of stuff trying to find a couple of mini servos I had I ran across a bilge blower for my boat. Its kind like a ducted fan set up and would probably be short lived but im just dying to stick it into some water and see what happens

[darrenervine]

Great points...
Funny you said the blower......I was looking at one yesterday while searching online for the Rule bilge's.
Think that would work too, interested to see how "waterproof" they are...

I heard someone say that computer fans are sealed....wonder if they would work....??

I am a pretty avid boater and my boat has a 225HP merc and I am constantly changing props...playing with diameter, pitch and number of blades, to see how it impacts performance..

A lot of builds seem to have motors that are spinning way to fast and in essence will maybe create overcavitation which results in air bubbles or slippage.

I would rather have a "tug boat" type propulsion than a "racing hydroplane"...
Slow and beefy with control rather than fast and tiny and all over the place...
Has anyone geared the bilge pumps for that kind of control?

DOE

When you look at professional/commercial ROV's....they seem to look like computer fans where you can see the prop rpm,.. it is moving so slow...

[DavidF]

The larger rov's are running hydraulic motors and they are slow, so to give them the thrust they need they run large props, you probably could get the same trust by using a smaller propeller at a highr speed, but the real clincher is that seals are rated at surface feet per minute (RPM*shaft dia*3.14159) granted you could use a magneticall coupled set up, but there are issues there as well and why would you bother if you could just use a loaded lip seal?
Im charging the video camera now, going to splash the bilge blower this should be interesting! Oh yea, no they dont look very water proof....

[darrenervine]

Just put some silicone on them, you'll be fine...

Upload the video of the blower motor submersion to youtube, I gotta see this....