Propellers and Ducts

[Roboshack]

Hi PowerGlider,
hi propeller pros of this forum,

I’m currently fascinated by JavaProp. I used it to calculate the propeller generated thrust for a given motor torque and rpm on one side and propeller diameter and pitch on the other. It worked fine to get an idea how a setup performs.

But would’t it be great to design the “perfect” propeller for a given motor setup instead of using one of the shelf that fits 80%? JavaProp seems to be a tool to achieve that, but also a tricky one for unexperienced guys like me.

Nevertheless I would like to start a discussion here, how to use JavaProp and CAD software to design a propeller according to motor specs.

I started with the selection of an appropriate motor and ended up with the 290 KV version of the TP 5870.
With a 10s battery motor RPM is about 11k and torque about 3 Nm. The propeller diameter should be 80mm to fit into a given duct.

Before I configured the prop parameters I changed the fluid settings in the options tab to water by entering the following values…

After that I entered the basic parameters in the design tab:

As you can see I wanted to design a prop with 3 wings and a desired speed of 6m/s (= 21 km/h or 13,4 mph). I also checked “shrouded rotor” for a ducted propeller and “square tip” for the same reason.

After that I selected a mix of airfoils that come close to a marine propeller (found them in an other forum) and changed “angle of attack” to 1 in all sections (see screenshot). The default settings will generate a propeller with an aircraft-like geometry.

After that I returned to the design tab and pressed “design it”. I got the following parameters back:

The generated propeller thrust is 304N = 31kg. Pretty cool. On the other hand, efficiency is only 55% and loading is rated “very high”. Not that cool. A view on the “geometry” tab reveals the following.

Looks pretty much like a marine prop to my unexperienced eyes. After that I saved the propeller (wing) as “*.iges” file to be able to import it to Fusion 360.

This is quite simple by pressing the “save” button and name the file “filename.iges” to a folder of your choice.

The result in Fusion 360 looks like this…

Looks quite nice. But you can see, that the side where the wing usually joins the spinner is open. At this point I have more questions than answers to create a 3 winged propeller out of this.

Fusion 360

1.) How do I close the open sides of the wing in Fusion 360 to make the imported .iges file a massive or at least closed object instead of an open “hull”?

2.) How do I have to align and combine the wing(s) to a spinner to make ist a working propeller?

JavaProp

3.) Is there a database or website with custom marine airfoils that can be imported in JavaProp? Or is that combination of predefined JavaProp airfoils as I used them appropriate to design a real marine propeller?

4.) There also seems to be an alternative to JavaProp. Anyone around who tried this one?
PropGen

In general

5.) Did anyone here design a working propeller with JavaProp and a CAD software that performed as calculated? If so, please share your wisdom.

Would be happy to tackle this with your help.

Cheers,

Sascha

[PowerGlider]

I face the same problem when opening the igs in fusion. I am not able to convert it into a body which i could combine with the hub. Javaprop stores it as a boundary representation brep and you can convert it in fusion to a kind of spline object or a mesh, but it does not help.
I think there is one option in MODIFY in javaprop to set the trailing edge thickness. Try setting it to 0.
I have still doubts if javaprop is able to generate the correct geometry, because its printing in cartesian coordinate looking like an airplane making linear movement, but it has to go in circle. It cannot produce an interface to the hub, just mess in this region. The output has not much to do with commercially sold propellers, question is, who is right? Commercially might be good but somehow outdated, while javaprop might not be optimized for water propeller design.
To make it worth printing my own props, there should be a better design and analysis available.

I use the aluminium prop gobbla tested, thank you gobbla! I trimmed the diameter down to 17cm on a lathe and use it in a duct. It needs lots of torque most motors cannot provide without a reduction gear. I think the diameter can be reduced further. I just asked Bruno from Alien if he can provide a 6384 with less kv, he agreed.
So, which kv would fit your needs best? At which velo do you want to end with 12s?
Is anyone keen on learning how to make such an outrunner waterproof? Shall i set up a new thread about this?

[Roboshack]

Yes, would be very intersting to learn how you make them waterproof.

[VeFoil]

We were drawing 98A from the looks of it, but the amp meter started flashing and we couldn’t tell for sure. Something is up with that expensive amp meter worth $7.99… not sure why

We just ordered the Eagle Tree eLogger with digital screen and accessories for proper inline Volts/Amps, Motor RPM, and GPS speed w/ mapping.

FYI HobbyKing has the complete Eagle Tree line of products saving $51 from regular retail prices the parts we just ordered:

[moggieuk]

Sascha, thanks very much for the walkthrough of JavaProp. You are ahead of me in the actual CAD work but I did notice that your parameter for water Kinematic Viscosity is off … should be around 1.5x10-6 (i.e. you are missing a zero). Not sure what difference that would make. This is a great program and I hope we can collectively learn how to leverage it better…

[Roboshack]

Hi Moggleuk,

thank you for your hint! I corrected it in my settings. Fortunately it didn’t make much of a difference. I’m a bit lost how to fix my problems regarding the further CAD design process. I’ve read in other forums, that more experienced makers managed to design and 3d print or CNC mill marine propellers with JavaProp, so it should be possible. So let’s keep digging into this.

Cheers,

Sascha

[pacificmeister]

Hey @Taylor, see ^^ … To help everyone with the CAD design here we should look into hooking your new parametric Fusion 360 prop setup to read blade shapes that come out of this JavaProp tool.

[Roboshack]

Hallo Meister,

would be glad to share a JavaProp blade with you and Taylor to hook it into the parametric Fusion prop.

Cheers,

Sascha

[LIftAss]

my friend has a CUDA underwater scooter with quite alot of trust. They use a very similar propp with adjustable pitch, I had some ideas to test it one day too.

Propeller Replacement Kit [010-kit-prop-system] - £135.00 : Deep Ideas Ltd,...

[VeFoil]

Wow ya thats amazing, and great to see that prop blade design else were as that is exactly what our prop software is showing us is the most efficient for the thrust and RPM we are looking to use. Thanks for sharing!

[LIftAss]

they seem to have made a gearbox for their new model too

Gears:
https://dive-xtras.com/wp-content/uploads/2015/11/019-1000-BOM.pdf

Prop assembly:

https://dive-xtras.com/wp-content/uploads/2015/06/propellerassembly.pdf

[LukePL]

It looks very promising but for low speed I think. I’ve got and info from them that the prop has around 200rpm in the water at lowest speed.

[keith75]

hi, its interesting, i could buy that propeller and shroud assembly and give it a test,and see the results, im still a bit away from testing tho, you said 200rpm is its speed, what do you think will happen putting 3200rpm through it, wonder if it could handle it, or would it warp with the stresses,

[keith75]

it seems so slim in its design, compared to an outboard engine propeller etc, does having a larger surface area help with thrust, i haven’t got a 3d printer, so im trying to source existing parts out there, all though a friend has a few laths and things, planning to make most of the parts with alloy

[pacificmeister]

We found the perfect prop! Don and I at Autodesk University

[Roboshack]

Hi PowerGlider,

I got in touch with Lars Christensen (Fusion 360 guru with an own Fusion 360 tutorial channel on YouTube). He came back to me with a very simple solution. Once you imported the hull as a *.iges file from JavaProp, you switch to the patch workspace…

After that you select “create/ patch”…

Then you select a boundary edge of the airfoil “hull” and click “ok” in the dialog box. (do this for both open ends of the airfoil)…

This enables you to transform it into a “closed” hull. Last step is to “stitch” the three surfaces together to one body. Just select “Modify/ Stitch”, select the three surfaces and click on “OK”.

The result is a regular Fusion 360 body that can be integrated in a propeller design.

I also got in touch with Martin Hepperle (author of JavaProp) and asked him some questions about hydro prop design. He confirmed, that JavaProp is able to design proper hydro props but under consideration of some basic conditions. It’s a very long reply with lots of propeller voodoo in German. As soon as I have figured it all out and translated it to English, I give you an update on this, if you like.

@pacificmeister / Taylor: Now we might also be able to incorporate JavaProp propeller blades into you parametric propeller design?

Cheers,

Sascha

[VeFoil]

Great Job @Roboshack !!!
Cant wait to test a prop specifically designed for the speed, RPM and torque each of our setups provide… !

[keith75]

hi everyone, its good to see a tailor made design in the works, brilliant*
has anybody ever tested one of these prop/duct assembly’s, i was thinking to test the 150mm model, and maybe try different props using the duct body, i don’t want to risk buying one if there no good for the job

[Hiorth]

the duct on those propellers look like kort-nozzles. (low performance) you should go for rice speed nozzle (high performance nozzles with airfoil cross sections, not straight).

[Jezza]

Actually with a efoil at max speed, a thin straight nozzle, purely designed for that would most likely be better. Both kort and rice nozzles are designed to give enhanced thrust at lower speeds. They do this by reducing tip losses. But eventually he shroud becomes drag at high speeds.