Standup Zone Forum
The Foil Zone => Foil SUP => Topic started by: DavidJohn on May 03, 2019, 07:27:58 AM
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https://www.audi.com/en/experience-audi/inspiration-and-lifestyle/sports/e-tron-e-foil.html
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I like the coaxial thruster, but I fear that such a small duct4ed propeller will be much less efficient versus a bit larger open propeller. Safer though...
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I'd prefer to do a jet pump, it could be nearly as efficient once the board is moving and a lot safer, but to get equal thrust for takeoff when the water at the mouth of the intake is not moving requires higher power. The easy way to get more power at a reasonable RPM is larger diameter motors, but that means excessive drag. Smaller diameter motors would have to rev high and have substantial gear reduction. My plan was to connect a number of small diameter brushless motors inline--output shaft to input shaft and rev the crap out of them. Then add planetary gear reduction and a two-stage impeller. I did find a suitable reduction gear--but it's a couple of thousand bucks. Too expensive to smoke with some guess-and-cut engineering.
My current plan is four ducted fan RC plane motor/fan units arrayed two to a side in place of a fin. Total weight less than two pounds, drag=huge, but as soon as it comes out of the water it will just be a somewhat heavy weight at the trailing edge of the mast. Two pounds of battery will be enough for 20-30 liftoffs. No electronics other than the ESC's--just a push button to give full thrust. On or off. Yeah, sure I could do a wireless throttle with a couple of ESP32's, but the idea isn't to ride under thrust, it's blast off and then ride swells. And the cool part is, I've got all the bits in a junk drawer, leftover from a ducted fan drone project that turned out to have huge stability problems.
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Its going to be interesting to see where foiling innovations will take us over the next decade. Probably need to be a powerball winner to afford it....