100mm Dia. ROV Prop

[rovbuilder2]

Hello,

I am making an ROV with a thruster having a prop diameter up to 100mm. The prop will be in a rice nozzle and the motor driving it will have an output of up to 100W. Does anyone had a 3d model of a prop I can use in any 3d format? I can scale it to size if it is not correct using Solidworks. I then have a machine shop that can CNC it for about 75 USD each. I am not too specific on the motor speed/torque because I can adjust it as required with different gearing. The hub of the prop may have to be big because my 50mm motor housing is directly in front of it. If you know the approximate thrust, that would be helpful too.

Thanks in advance for the help.

Jeff

[Submarine Tom]

A model airplane prop would be your best bet by far, and they're cheap.

Guessing: 20 N thrust

-Tom

[rovbuilder2]

Hello,

Are you sure I don't need a Kaplan style prop? This is a school project, so I cannot just go out and buy a $5 airplane prop and call it a day. Need some thought and a little theory behind it. Trying to get the highest efficiency prop for the battery power. I would prefer a custom prop I can have machined by CNC.

Basically we are trying to improve on a design that puts 40W into a motor and only gets about 2-3W in forward movement out of the ROV. The forward movement is 1.2lb @ 1.4 ft/sec. The output on this motor shaft is 20W.

Our new design will input 100W and the motor shaft will output about 75W. I would like to see as much of that converted into forward motion as possible. PropCad is a little expensive to use here, but if anyone has a copy, maybe they could input this data and export a 3d model? Maybe its not that easy.

Thanks,
Jeff

[Submarine Tom]

Jeff,

I don't mean to sidetrack your project but from a practical point of view, performance R/C airplane props are really really good for a low power, efficient vessel like what you describe. You can get them in many diameters and pitches and they are very inexpensive. I'd try one that is 100 mm X 80 mm pitch. If you really want a cnc one then model it after the R/C one that you find works best. The hobby shop would probably even let you exchange them if you could keep them untarnished during your trials.

Have you tried JavaProp software? Depending on your advance speed (velocity through the water), you may even use a square prop (100 X 100) and reach efficiencies of 80%! JavaProp is brilliant and allows for modifications. Google it and start designing. You can also make your own prop from steel, stainless or otherwise. It's not as hard as you may think.

What shape is your ROV design? Target speed? Drag? Pictures?

This may be of interest to you: http://www.homebuiltrovs.com/rovforu...c.php?f=3&t=27

-Tom

[rovbuilder2]

Hello Submarine Tom,

Thank you for your input so far.
ROV is round 300mm diameter with thrusters out each side. I do not have any pictures yet. I would like the speed to be between 2 and 3 knots if possible.


The ROV I am trying to approve upon that uses 62mm diam props with 2 blades on a 45 deg. angle.....so I guess this makes the pitch 195mm? In fact it looks a little like an airplane prop. The little motor spinning the prop is running 1400 rpm and 1 kg.cm in a bad range of its efficiency curve - about 38% efficient I think. Volts in is 19, amps, 1.8A. I know there is some losses in just spinning the drive train fast in the water even without any prop so it would be better for me to use a gearbox and slow it down a little in order to avoid these losses and hopefully hit a better range in the motors efficiency curve.

I will take a look at Javaprop too!

Thanks
Jeff

[Tim B]

For a school project you'll only need to try a few different props and quantify the efficiency. Propeller theory is a complex subject that only a small number of people really understand (I certainly don't!). However, what most people DO understand is thrust/torque/efficiency (kt/kq/eta) vs RPM. There is plenty of info on the web as to how to build a simple test rig, which should only pose a minor challenge to a man with a technology and physics department at his disposal.

Good luck,

Tim B.