Sorry for the delay. Was busy with work and dealing with my boss.
I’m getting an error saying only pictures can be uploaded. As such you will find all the files needed from the motor back in the dropbox link provided. PLEASE NOTE all the files are designed to be printed on a Prusa i3MK2S in Polymaker PC-Max. I’m not sure what will happen if you print them in any other material or printer! Please pay attention to tolerances of your own printer**
Does anyone sand their 3D printed propellers? Having a smooth surface would be critical to efficiency, specially since they are spinning so fast. I sanded a test piece of PLA to 600 grit and it polishes up really nice! I’d love to hear about someone’s before and after test results (I’m not to that point yet).
Yes sanding does help. Hard to say how much but I believe I can feel the difference. My neighbour works in the jewelry business and he has some great sanding tools, give him my props and he brings them back super smooth
“To understand why most waterjets have the nozzle above the on-plane waterline, let’s take a look at where the thrust of a waterjet comes from.
Ignoring for the moment the internal components, a waterjet is a classic example of Newton’s laws at their simplest - for every force, there is an equal and opposite reaction force. Force is the product of mass times acceleration, or put another way, the rate of change of momentum.
To apply a forward force on the boat, the waterjet accelerates a large mass of water in the opposite direction. In early prototypes, with the output nozzle underwater, this posed a problem. Water is dense and incompressible, so the outlet stream quickly encountered a lot of back pressure from the surrounding water. It’s very hard to get a high flow rate at a high speed with the surrounding water resisting the output stream (momentum = mass * velocity). Thus it quickly becomes very difficult to give the water leaving the jet a significantly greater momentum than the water around it.
When we move the outlet above the water, this picture changes. Air is compressible and about 600 times less dense than water, and so presents very little back pressure. Now it’s not nearly so difficult to get the outlet flow to have both a high volume and a high speed, thus the change in momentum of the water through the pump is higher, thus the force is higher.”
The first time I saw an electric jetboard I though how fun it would be to put a foil on one. The design in my head was to suck the water up through the mast and out the back of the board. I noticed on my Waverunner that the water shoots out above the waterline so I figured it would work to have the water shoot out the back of a foilboard. Then I ran across this video which confirmed the idea would be possible:
It wasn’t long after that when I saw a video of the Jetfoiler and that concept looked more practical. But according to Simon there may be some benefits to shooting the water out above the waterline.
Hi Simon, my current values and speed come from my own personal arduino hacker set up and should be taken with a grain of salt. I’m pretty confident that the numbers I’m recording have alteast +/-10% accuracy. The prop was designed for me and my own setup to minimise slip and maximise efficiency. It will vary setup to set up.
Hey Guys, A backer of my Kickstarter Project found a really good program for wing foils and props both air and water. It helps you designed and test everything on the spot with JAVA based program. I have not yet read through the entire site but looks interesting.
You can even select the prop surface finishes…:
Smooth
Painted
NACA Standard
BUGS AND DIRT… yes, this is an option
Hi @Graystorm44. I didn’t calculate pitch. Maybe you can? Have a look at the CAD here. I have successfully used the 3 and 4 blade props created with this parametric prop setup and the default parameters. The Fusion setup was since improved by @Taylorhere. You can quickly adjust all the curves to modify size, shape, angles… resulting in pitch changes.
Have a look at the CAD