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; maybe one of them would work on this hull....
They can't make something as small as I need. 
Gotta go fire up FE Calc and see what I can do with off-the-shelf stuff. The trouble is I need counter-rotating pairs, so that really limits the selection.
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Bummer! They can't make something as small as I need.
Gotta go fire up FE Calc and see what I can do with off-the-shelf stuff. The trouble is I need counter-rotating pairs, so that really limits the selection.A nation of sheep breeds a government of wolves -
Vid From Last Week
And it was running kinda slow....., but it WAS running.
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One of the challenging issues in building and running the micros is propeller selection. There aren't a whole lot of choices out there. So I fired-up my trusty old version of FE Calc and started toying with propellers. Small diameters with a high pitch gave the best calculated results, but real-world testing shows that kind of prop can be slow to "hook up". After toying with FE Calc it looks like a 27mm diameter prop with a 1.6 pitch ratio should do better than 31 mph (not bad for a tiny hull on 2S and under 20 amps). The numbers were well within the parameters of the motor and the ESC without the need for additional water cooling. A 3-bladed prop should help with hooking up out of the hole.
So where would someone find a 3-bladed, 27mm, 1.6 pitch ratio prop with a 1/8" bore?
As it turns out a 32mm prop with a pitch of 1.4 would theoretically travel 32mm * 1.4 = 44.8mm per revolution. A 27mm x 1.6 prop would travel 27mm * 1.6 = 43.2mm. Those are pretty close! 
Reducing the diameter of a prop doesn't change the theoretical distance per revolution so take a "432" prop and cut it to 27mm and Voila! You have a "627" prop.
I bought a pair of these: https://www.ebay.com/itm/uxcell-2Pai...72.m2749.l2649 because FE Calc gave good numbers for running them on my Micro Scat Cat Twin. They are made from quite rigid plastic that shapes well and will take a sharp edge. Could be just the ticket for sub-200 Watt boats.
I'll report results after next Monday, March 9.
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cant wait to see a vid of that round nose running with a good prop on it. one day I hope my sister will bring mine up here LOLComment
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Here's a vid of the very first run of the Short Circuit at Santee Lakes with a de-tongued X427. I posted it earlier, but it hasn't had many views yet. You can see it takes a bit for the prop to hook up, but after that it runs pretty good, but not blisteringly fast. More pitch should speed it up a bit.
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Did some more testing today. The 3-bladed "627" prop worked OK, but the motor got hotter than I like. I lost a motor mount screw in the Atlas so testing was cut short on it. I ran the Short Circuit several times, and while slower, it seemed to like the de-tongued Octura X427 the best. I tried a couple of X427s in my inventory and they all seemed fairly equal.
Here's a vid of the Short Circuit on 2S with the X427.
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Epilogue
I think it's time to call the research and development on the 1:20 scale hydro project done and move on to other projects.
It looks like I'll settle for the "adequate" speeds I'm getting with this setup. In order to keep temperatures within reason, I need to run really small props. On one of the Atlas tests, I let the smoke out of one of the little black boxes in the ESC; additionally, the motor was WAY too hot (155 degrees). Actually, it was just one of the FETs that had a "minor" puff incident, but it still rendered the ESC dead for future use. It was a different ESC from what I normally use; maybe that brand had a quality issue in one of the FETs. Furthermore, that smoke release happened when running a CNC 632 prop. The boat was wicked fast and loose with that prop though.
The solution to the speed issue is pretty obvious: Time to think about water cooling so I can turn that 632 prop without burning things up. The rudder I'm using has an inlet, so the prototype may soon go with a water-cooled inrunner, and I'll add water cooling to the existing ESC. The two running air-cooled boats will remain as-is. They're fun to run and super-stable, they're fast enough to impress spectators, and they look WAY COOL doing it. Maybe someday down the line I'll build the 1980 Dr. Toyota in 1:20 scale with a water-cooled 11XX Neumotor and do insane speeds with it. I don't know if the roundnose would like that much power. Perhaps I'll build the Hawaii Kaii sometime way off in the future and find out.
The air-cooled boats run a long time "as-is" with a 1.8 mah LiPo; and with the cut X427 prop, the motor temps stay within limits. This combination with the great stability it has would still be fun for deck-to-deck spec racing. The Short Circuit only needs a driver figure to be called done and the Atlas just needs a bit more paint and gluing all the scale detail parts together to be called done.
I'll post photos and vid links here if there's something interesting to show.
Stay tuned...A nation of sheep breeds a government of wolvesComment
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18 Months Later:...........
The summer flying season is over. Time to play with toy boats. The Evil Doctor has been busy, so stay tuned for lots of fun stuff. The paint "Aw$#!+" on the 1:20 Atlas has been fixed and a coat of clear shot on the deck. I'll do a bit more clear on the deck, sand it out with 2000 wet/dry then do the same on the bottom.
The Atlas should be ready to go soon.A nation of sheep breeds a government of wolvesComment
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While the paint is drying on the Atlas, there is one thing the Short Circuit needs.
Can anyone watch this vid and tell me what it is?
A driver of course. I'm working on getting some PROPER 1950's driver figures made. Here are some preliminary renderings; I want to move the head a bit to one side so he doesn't look like a stiff dummy.A nation of sheep breeds a government of wolvesComment
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First full-color mock-up. Still needs more clear and some cockpit work, but it's close.A nation of sheep breeds a government of wolvesComment
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Some refinements on the driver figure......
50s-hydroplane-driver_update.jpg
Might even make separate head/arms for better posing....
50s-hydroplane-driver_cut.jpgA nation of sheep breeds a government of wolvesComment
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Can you fit a 1.4g servo inside him to turn his head?Paul Upton-Taylor, Greased Weasel Racing.Comment
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Everybody knows you want to keep the edges on the ride surfaces as sharp as possible. At 1:20 scale, some of these can be a task to keep sharp. For example, the little step on the bottom of the sponson is only about 1/16" at its deepest.
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I discovered the best ever sanding blocks for this kind of fine detail. There are always sellers on eBay selling scrap Delrin from their shops. You can get a few or a lot.
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Simply use some spray glue to attach 320 grit wet/dry sandpaper to the block of the right size. You can trim the paper to a perfect sharp edge with an X-Acto knife.Last edited by Dr. Jet; 09-21-2021, 02:46 PM.A nation of sheep breeds a government of wolvesComment
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Well, I have more then enough 1:20 scale driver figures on their way. Stay tuned for a review.A nation of sheep breeds a government of wolvesComment
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