Who wants to build a semi-scale all-wood micro hydro?

[Dr. Jet]

Fall of 1971 [Eeek]- Wurtsboro Airport upstate New York

All I can remember is that when the towline drops off the silence is mesmerizing......

It's quiet with a sports canopy?

I traded my trusty H-301 Libelle for the venerable 1-26.

[old guy]

I used to go gliding when I was younger its lots of fun nothing like it

[Dr. Jet]

Hey OG, have you started building your shovelnose?

[old guy]

Hey OG, have you started building your shovelnose?

No its still at my sisters place not sure when i will see it

[TonyRomano]

Video of the very first run of the Short Circuit Shovelnose. There was a lot of grass in the lake and I wound up towing a lot of it around.

https://www.youtube.com/watch?v=pUECqAqElt0

Looks “zippy”! Is the idea with that hull less drag? (Contact with water)


Sent from my iPad using Tapatalk

[Dr. Jet]

Looks “zippy”! Is the idea with that hull less drag? (Contact with water)

That's the whole idea behind a 3-point hydro. The sponsons are just there to keep the hull level on the water. In a perfect world, only 1/2 of the prop would be in the water and the sponsons would "dance" on the surface just enough to keep things under control. The entire hull would ride on a cushion of air. It pretty much does that when running straight, but turning creates a lot of water drag. In the video, you can see it accelerate rapidly as it straightens out in the backstretch after turning.

The other idea with that hull is to make a semi-scale model of a full-sized boat.

[TonyRomano]

Thanks Dr. Jet!


Sent from my iPad using Tapatalk

[Dr. Jet]

I still have a handful of kits available......

[trialsguy]

I still have a handful of kits available......

Which kits are available? And what does the kit include? Thanks!

[Dr. Jet]

I may have a couple of each (Atlas and Shovel) left. They include everything but a receiver, a battery, and finishing materials.

[Dr. Jet]

I managed to run the Atlas Prototype and the Short Circuit today. The Atlas was blistering fast with good handling. All it needs now is some fine-tuning on the setup and it will be done. This thing is great.

I also ran the Short Circuit. It wasn't quite as fast as the Atlas as I used different props on each of them, but it too had impeccable handling and can easily do full-throttle corners. It too only needs a dialed-in setup to be a champion.

[old guy]

next time you take them out take a video for us thanks now you have them set up

[Dr. Jet]

I tried to get a videographer last time out when I first arrived, but everybody was preoccupied with flying their float planes. I think they suspected another slow and boring boat. Once I ran the Atlas, there was some jaw-dropping and an attempt was made to take a video, but he couldn't get his camera to work. I plan to go out again on Monday, March 9th and there may be more incentive to video this time out and I'll have him use my cell phone to take vids.

[old guy]

thanks what prop did you run on the atlas and will you be trying it on the round nose

[Dr. Jet]

The first time I ran the Atlas at Santee, I used a plastic X430 that I had de-tongued and cut down to 28mm. It actually ran pretty good. When at my new pond, I tried a bigger prop, 32mm I think. Things got kinda hot, so I'll try a smaller prop next time around. I tried the Short Circuit on a beryllium X430 that was cut and de-tongued. It would cavitate if full power was applied at a low forward speed. If you gradually accelerated, it would finally hook up and run pretty good, but not nearly as fast as the Atlas. That prop was too small. Next time out, I'll try some cut and reduced X632s.

I'm talking with one of the CNC prop manufacturers about having some "Special" props made for some of the new top secret projects under research and development at "The Stinkbugworks" ; maybe one of them would work on this hull....

[Dr. Jet]

........ I'm talking with one of the CNC prop manufacturers about having some "Special" props made for some of the new top secret projects under research and development at "The Stinkbugworks" ; maybe one of them would work on this hull....

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.

[Dr. Jet]

And it was running kinda slow....., but it WAS running.

https://www.youtube.com/watch?v=CK34...ature=youtu.be

[Dr. Jet]

thanks what prop did you run on the atlas and will you be trying it on the round nose

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.

[old guy]

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 LOL

[Dr. Jet]

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 LOL

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.

https://www.youtube.com/watch?v=q6ffpDiJ0Xs

[Dr. Jet]

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.

https://www.youtube.com/watch?v=fqKzuRaCiXk

[Dr. Jet]

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...