Timing Belt Reduction


@WNT, I have been efoiling with printed plastic 2 bladed props for many months without problems. I keep switching between 2, 3 and 4 blade props. That’s with my geared setup, not the belt yet. What setup are you using to efoil, can you share your rig?


To pacificmeister: I use scientific materials for propeller design - a special physical rule and special design and computational formulas. These subheadings are new, so they are not applied to any software.


To Just: If I see a good propeller somewhere, I’m very pleased to praise it. For example, I commended the impeller from Virus here - https://forum.e-surfer.com/t/diy-components-from-mhz/48/2


Hi @pacificmeister, How is it going with the belt reduction? Did you have a chance to test it in water already? I also have this SSS360Kv motor and 80mm aliexpress kort, as below. I will appriciate if you can share your design and part list (belt and so on…), since this kort is most efficient on 7000-8000rpm range, which is exactly your design, providing 180kv and 7560rpm on 42v. I would defenitelly try this system with my ordered kort.



I wish I had better news but my test this weekend didn’t go well. The belt slipped off and got chewed up. I think I know why, the pulleys were offset too much after I added a thrust bearing. The belt didn’t run in center anymore, likely partially off the pulley. Will mod and try again. Waiting for new belts now which will take another week. Maybe I’ll post a failure video in the meantime with build details.


Looks like your pulleys do not have flanges on them. Any reason why not? SDP-SI goes so far as to say that flanges are necessary in a timing belt system - see section 9.8 here

Also, it looks like your design uses 3d printed parts to locate the two pulleys. I’d be concerned about angular misalignment between the two since I don’t see any hard locating features (e.g. pin and hole) to keep the two halves aligned. In a perfect world I’d try to use machined plates to locate the timing belt assembly and then have a fairing that provides the seal around that assembly, that is decoupled from positioning of the timing belt.


Thanks @nmcma I appreciate your thoughts. I took the flanges off on oposite sides of either pulley, this allows me to have the pulleys only 1mm appart and minimize housing drag. Each pulleys remaining flange should keep the belt in check. Should work if they are aligned, on my skateboard I also don’t have a flange on the inner side of the wheel pulleys and it stays on. But you are right, shaft alignment may be an issue.


I just posted an update about my recent belt drive tests. No success so far but I am not giving up yet.


nice work! @pacificmeister


Hello Pacificmeister,

maybe you know already, but here you can find a calculation tool for toothed belt drive. It gives you everything like the shaft offset, max power …



So interesting to watch your video! I really like the belt drive idea!
Btw, Is Vitali your neighbour?


Love the setup and work you put into it but I’m building a efoil/board as well and im of the KISS type of method of keeping it simple stupid. but why not just use a SK3 6374 149kv outrunner direct drive? I know the outer can is I little bigger but with proper farings, the benefits v.s drag I think would pay off. The outrunner would have the torq needed.


What caused most of your leaks in the electronics housing, so we can avoid them?


Hi @Chris_wilson. Done it and it burned up in seconds. See here: For who try/have tried direct drive with outrunner. With a milled motor mount attached to an aluminum mast for better cooling this may work… but heat transfer is a problem, especially also because you will likely run this motor at max capacity to get up on the foil, if it even has enough power with its 2250W. But don’t want to discourage you from trying, I agree it would be fantastic if you get it working. I am all for KISS and cheap setups. Good luck and please keep us posted.


If your PLA prints leak like a sieve like mine did initially, look at my two posts here: 3D printing, how do you do it? (3D printing, how do you do it?)

I printed my ESC’s watercooler for today with those settings and glued it to aluminium stock. The test with an airpressure of 3 bars showed no signs of leakage. I can only recommend investing some time in a watertight print test, it easily pays pack in saved time for epoxy or paint coats.
If you are using Cura as Slicer for 3D printing here is my current watertight print profile for cura3.2.1

DIY Waterproof remote

I assume opening and closing the lid a lot damaged the seal. Nothing visible but it seems to get worse. I now put a lot of marine grease on the seal before closing. These electronic enclosures are not made for constant opening and closing, so not ideal for prototyping and testing. If I’d do it again today, I would use a Seahorse box for electronics, probably a slightly smaller one than what I use for my batteries. This box has kept a great seal and I open/close it a lot more than the electronics box.


@pacificmeister, thanks for the info I’ve accumulated a lot of motors, pumps and esc for a surfboard build, now i want to do a foil so the custom 68mm pumps wont work, the water cooled T20 is rated @5000W but has 720kv so need to gear it for a prop vs pump.


Dear Pacifc Mister,
If you wear this type of belt maybe you will not have any more problems.
Hope this helps,



A plain ribbed belt won’t have the “grip” to drive this kind of setup, it will almost definelty slip, a bit more trial and error pacificmeister and you’ll get it working.

You could try flanged cogs it’ll help with keeping the belt aligned


Hi, Chris_wilson, I finally see on the forum an impeller from high quality aluminum. It’s clear from the photos that you have almost everything to produce a quality jet propulsion. Only some components that are not too stressed can be printed from cheap material on a 3D printer.