Electric Surf Board

[ropower86]

Wow, you are flying and putting this together pretty fast! Do you have some engineering background in the watercraft field or some sort? It had taking me a verrrrrrryyyy long time to put a jet drive together.

About your tig job you did pretty good, I use to be a top-flight in tig welding, I had the welds coming out like a roll of gold coins. But that was 13 years in the field but I opt out because I now have bad eyesight.

cheers. i dont have engineering background with watercraft. but i do have 20 years in automotive design manufacturing.

do you have some pics of some of your old welding projects? would be cool to see those perfect welds!

I have pictures but I have it on the flash drive stashed in my safe box in Florida. But I will check my computer for any pics.

[srn]

here my mould out of PE.

How many impellers have you made out of the PE's negative mold?

At the moment two. The second one has already the quality that I want for my prototype.

[Frizzo]

Hey ropo, here is a tutorial for designing a propeller in inventor:

https://www.youtube.com/watch?v=-iVDzhGvre4

for the cast, just do a boolean difference between the propeller and a block of the right size. then you could also 3d print or cnc machine the mould. If you 3d print it, then use ABS so that you can smooth cemically the surface. I´m planing right now to cnc it. Sadly I have not a cnc mill and no 3d printer. So my progress is really really slow, since I have tro wait for others to get my stuff done.

[srn]

I used PE because Epoxid Resin should not stick to it.

But because of a too rough surface, it is sticking like hell ..

For my second Impeller, I applied normal candle wax on the surface.
This worked very well.

[ropower86]

Hey ropo, here is a tutorial for designing a propeller in inventor:

https://www.youtube.com/watch?v=-iVDzhGvre4

for the cast, just do a boolean difference between the propeller and a block of the right size. then you could also 3d print or cnc machine the mould. If you 3d print it, then use ABS so that you can smooth cemically the surface. I´m planing right now to cnc it. Sadly I have not a cnc mill and no 3d printer. So my progress is really really slow, since I have tro wait for others to get my stuff done.

Frizzo, thanks for the video. Now I just have to make time to watch and learn. Yeah, it sucks not to have access to these wonderful machines. I had to get me a 3d printer and it is amazing just to print parts at home, I was paying a guy to 3d print parts for me and it adds up really fast it gets really expensive. I am in the same boat as you as it is a slow process making parts.

[ropower86]

I used PE because Epoxid Resin should not stick to it.

But because of a too rough surface, it is sticking like hell ..

For my second Impeller, I applied normal candle wax on the surface.
This worked very well.

You should use pva film that is used in mold release to make it a whole lot easier for you. By any chance do you share your cad file of the mold?

[chris_kline]

theres some pretty good advice, 3d printing moulds. i saw 1 guy who built a hydrofoil was just 3d printing his props and bolting them straight on. i had one 3d test printed, and i think if i beefed up the design a little, it would be strong enough to just use a 3d printed part

[chris_kline]

heres some pics of my mould, and the prop that came out of it before cleaning it up. pretty much the same thing as srn did with his pe mould.

[chris_kline]

i cant seem to add cad files here. am i doing something wrong?

[srn]

heres some pics of my mould, and the prop that came out of it before cleaning it up. pretty much the same thing as srn did with his pe mould.

looks very good

[chris_kline]

heres some pics of my mould, and the prop that came out of it before cleaning it up. pretty much the same thing as srn did with his pe mould.

looks very good

thanks

out of curiosity, what pitch did you put on your blades? looks good, im just curious if we ended up around the same ballpark figure

[srn]

thanks

out of curiosity, what pitch did you put on your blades? looks good, im just curious if we ended up around the same ballpark figure

My pitch is 57mm, diameter 60mm.

[ropower86]

About the 3d print impeller, Yes it does hold up pretty well in the water even with tremendous loud. The impeller has to be printed at 100% infill, in 0.1mm or 0.2mm and set as a high quality which takes longer. Yes, it was in PLA.

[Frizzo]

When do you actually upload the video at full trottle, ropo? I´ll be very interested to see what is possible to take out from your motor.

Also, I wrote to MHZ and ansked how much torque the Scorpion HK-7455-320KV has.... It has a 7,2 Nm Torque.

Here is the data table of my Lehner 3060/9

Lasttabelle 3060.png (20.54 KiB) Viewed 3464 times

If I don´t understand it wrong, I could get about 250 Ncm torque by ca. 45500 rpm out of it, right? If I then add a 3:1 gearbox, I should get about 750 Ncm =7,5 Nm from my motor and ca. 15.000 rpm, wich is exactly the rpmrange we are using for our jets. I could, in that way, obtain about the same torque of the Scorpion sold by MHZ without spending 1000 €.... Or am I somehow wrong?

Cheers

[chris_kline]

When do you actually upload the video at full trottle, ropo? I´ll be very interested to see what is possible to take out from your motor.

Also, I wrote to MHZ and ansked how much torque the Scorpion HK-7455-320KV has.... It has a 7,2 Nm Torque.

Here is the data table of my Lehner 3060/9


Lasttabelle 3060.png


If I don´t understand it wrong, I could get about 250 Ncm torque by ca. 45500 rpm out of it, right? If I then add a 3:1 gearbox, I should get about 750 Ncm =7,5 Nm from my motor and ca. 15.000 rpm, wich is exactly the rpmrange we are using for our jets. I could, in that way, obtain about the same torque of the Scorpion sold by MHZ without spending 1000 €.... Or am I somehow wrong?

Cheers

the logic is sound.

i wonder where MHZ or scorpian get/derive their figures though. 7.5nm @ 15000 rpm is 11kw of mechanical power output.
the mhz website says the hk7455-320kv has 22.4kw of power.

https://www.mhz-watercraft.com/shop/en/ ... t-80?c=114

and what the hell is current power -14 kw? does that mean continuous power? either way both figures are significantly more than 11kw.

not sure if maybe theres some subtleties to this electric power thing im not aware of (im new to it and here to learn) or if theres a little bit of BS going on?

in my opinion, i think 11kw should be more than enough power, if all the other factors come together, board/prop/jet efficiency etc.

i guess were gonna find out!

[ropower86]

When do you actually upload the video at full trottle, ropo? I´ll be very interested to see what is possible to take out from your motor.

Also, I wrote to MHZ and ansked how much torque the Scorpion HK-7455-320KV has.... It has a 7,2 Nm Torque.

Here is the data table of my Lehner 3060/9


Lasttabelle 3060.png


If I don´t understand it wrong, I could get about 250 Ncm torque by ca. 45500 rpm out of it, right? If I then add a 3:1 gearbox, I should get about 750 Ncm =7,5 Nm from my motor and ca. 15.000 rpm, wich is exactly the rpm range we are using for our jets. I could, in that way, obtain about the same torque of the Scorpion sold by MHZ without spending 1000 €.... Or am I somehow wrong?

Cheers

I did made the video of the open throttle but my phone crap out on me I couldn't even load any video from my phone. When I tried to retrieve the file from the mini sd card onto my computer the card keep rejecting itself. I had the video of me going full throttle which I was going around 9mph and keep in mind I weighed 220 pounds. So I bought me the Samsung edge with a bad ass camera to record a new video then the pool closes because somebody drowned I had no chance to test it again because now it is. Till this day I am really upset that I lost pictures and videos of this project.

What I've learned that with any jet boards there is a weight limit where 170 pounds is the maximum weight for you to see good speed, over that weight limit the boards slow down tremendously even if you have the right board volume. Unless you have a 15kw or more brushless motor.

When it comes to calculation or bench testing everything tends to sound good until you put it in the water. There will be a percentage power loss because of fluid load to the impeller. You can be right or wrong with your calculations the only way to find out the true answer is to test it in the water. Gearing it will work for sure!

I will need to learn how to load pictures on here so I can post.

[ropower86]

When do you actually upload the video at full trottle, ropo? I´ll be very interested to see what is possible to take out from your motor.

Also, I wrote to MHZ and ansked how much torque the Scorpion HK-7455-320KV has.... It has a 7,2 Nm Torque.

Here is the data table of my Lehner 3060/9


Lasttabelle 3060.png


If I don´t understand it wrong, I could get about 250 Ncm torque by ca. 45500 rpm out of it, right? If I then add a 3:1 gearbox, I should get about 750 Ncm =7,5 Nm from my motor and ca. 15.000 rpm, wich is exactly the rpmrange we are using for our jets. I could, in that way, obtain about the same torque of the Scorpion sold by MHZ without spending 1000 €.... Or am I somehow wrong?

Cheers

the logic is sound.

i wonder where MHZ or scorpian get/derive their figures though. 7.5nm @ 15000 rpm is 11kw of mechanical power output.
the mhz website says the hk7455-320kv has 22.4kw of power.

https://www.mhz-watercraft.com/shop/en/ ... t-80?c=114

and what the hell is current power -14 kw? does that mean continuous power? either way both figures are significantly more than 11kw.

not sure if maybe theres some subtleties to this electric power thing im not aware of (im new to it and here to learn) or if theres a little bit of BS going on?

in my opinion, i think 11kw should be more than enough power, if all the other factors come together, board/prop/jet efficiency etc.

i guess were gonna find out!

That 320kv more does produce a lot of power at the same token it consumes more energy to create that kind of power. Meaning you need a lot of batteries and a top quality ESC to handle the motor demand at 11-14kw. The 1.35 high-quality magnetic wire in this motor has very low resistance where it can handle high amps which will create less heat that equals to power gain. What is the kV on your motor? 11kw is more than enough for a surfboard.

Oh I forgot, mhz has there testing equipment check out the video

https://youtu.be/NrxSkkfGXlQ

[Frizzo]

The Lehner 3060/9 has about 778 rpm/V. Or at least that is what Lehner says. That value is in the Triangular configuration. In Star config. it has 1,73 factor less rpm/V = 450 rpm/V and gains 1,73 factor more torque = 240 Ncm/A in triangular = 415,2 Ncm/A in star... of course I have to test it since those are all theoretical numbers...

A 80 mm jet has an rpm of maximum 12.000 rpm. (discovered it only today. Should had done my homework better...) That means that if i take that motor in star config. at 59 V I would get about 26.550 rpm out of it. By adding then a gearbox in factor 2.2 I would get 12.068 rpm and 913,44 Ncm out of it.

But, again, those are all theoretical numbers...

And since I'm still a student, I'm kinda slow in developing my project... If there is someone in Germany building a surfjetboard too, give me a pm. It would be nice to cooperate and join our forces together.
It would be nice to discover if it would be possible to build a jetsurf with a simple gearbox instead of these really costly motors. (Lehner 7040 and Scorpion hk7455-320kv)

[ropower86]

[Frizzo]

to attach an image go here:

Screenshot from 2017-12-12 21-35-22.png (102.83 KiB) Viewed 2503 times

then, click on place inline

[ropower86]

to attach an image go here:

Screenshot from 2017-12-12 21-35-22.png

then, click on place inline

Are you kidding me!?!?!?! All this time I was struggling to add pictures for the longest since Ive been on here. I had never paid attention to the bottom.

[chris_kline]

Finished prop!

[srn]

Finished prop!

great work,
how did you make the screw thread ? Is this ready-to-buy part that you glued in ?

[Frizzo]

That's an amazing job!
Did you seal the edges with epoxy? How thick are the blades?

[chris_kline]

Finished prop!

great work,
how did you make the screw thread ? Is this ready-to-buy part that you glued in ?

thanks. the thread part is just an m10 stainless nut. the nut bolts into the mould before injecting the resin.

hand on ill take a photo of it