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acdii 04-08-2021 07:42 AM

Power for Duma Super Sport
 
I started building my kit, and want to put a brushless in, but don't know what motor to use. Right now I just have the framing done, getting the last pieces glued up before sanding. I figure if there are any mods I need to do, now is the time.

Retiredat38 04-10-2021 08:01 AM


Originally Posted by acdii (Post 12672257)
I started building my kit, and want to put a brushless in, but don't know what motor to use. Right now I just have the framing done, getting the last pieces glued up before sanding. I figure if there are any mods I need to do, now is the time.

Well, my first question for you is why a brushless for a boat like this? Nothing against it mind you but I consider a brushless as more of a performance motor. Not a pleasure craft motor. But to each their own.

While I am no expert so some of this could be off base. But given the response you've had so far (Why am I not surprised?......) I will attempt to get you going in the right direction.

On their web site Dumas recommends a motor/drive combo for this kit. While they recommend a brushed motor, it does give you a place to start. They show a motor that does 10,000 rpm unloaded and operates under load at around 8-10 amps. They recommend a 1.5" prop and a few pitches to pick from. I'd start by picking one or more props. The largest diameter with the greatest pitch will work the motor the hardest. And Brass ones don't flex like plastic will but they do cost more. So, where to next?

What voltage and battery type do you plan to run? Since weight or lack thereof = performance in a boat, I think I'd plan on a either a S2 (6.6 volts) or S3 (9.9 volts) LiFe.
Given the 10,000 rpm motor Dumas recommends, I'd start by looking for a brushless with a KV between 1000 (S3) and 1500 (S2). I'd be tempted to look for a 1200 KV and run it on the S3 battery. As for the specific motor, since Dumas lists a motor rated for 8-10 Amps I'd look for a brushless that runs in that general area on the voltage you select.
The speed controller or ESC. Given the 10 Amps Dumas lists I'd get an ESC rated at 20 Amps. Why double what Dumas shows? Safety margin is basically it. Plus the ESC won't work as hard and therefore run cooler. A 15 Amp would probably be OK but..................... Do you want reverse as well? Not as many brushless ESCs with reverse but they are out there and more all the time. Also get an ESC with the built in regulator for the radio receiver. Normally known as a BEC circuit. Last but not least, you can also go with water cooling on the ESC. If you get one with it, use it.

Hopefully this answers some of your questions. And probably raises more. Feel free to ask them. I'll do what I can for you.

acdii 04-10-2021 08:30 AM

I have a 30 amp ESC I was considering using, hence why an inrunner brushless came to mind. Now that I look around, a 20 amp brushed ESC with reverse aren't very expensive. I also was planning on Lipo for the power. I figured since brushless can dish out gobs of power I could use a smaller motor compared to the can Dumas used to save on weight.

mfr02 04-11-2021 12:46 AM

Inrunners tend to be good for high speed, low torque situations, i.e. a tiny prop spinning very fast. Most boats, even quite quick ones, tend to need torque to get them up to speed and then keep it. This often means outrunners driving a "boat size" prop.
Retiredat38's numbers look OK.

Retiredat38 04-11-2021 01:31 AM


Originally Posted by mfr02 (Post 12672603)
Inrunners tend to be good for high speed, low torque situations, i.e. a tiny prop spinning very fast. Most boats, even quite quick ones, tend to need torque to get them up to speed and then keep it. This often means outrunners driving a "boat size" prop.
Retiredat38's numbers look OK.

And from my understanding, all else being equal (or as equal as they can be) a lower KV means more torque. So that would suggest you'd want a lower KV motor and a higher battery voltage to get the operational rpm you want.

Now a shameless plug. My modeling experience has for years been the scale wooden sail boats for static display. I've only recently ventured into RC. That said I have had great dealings with a hobby shop in the UK. Cornwall Models

They carry a very broad range of boat bits and pieces for RC as well as static. Shipping usually isn't bad. Six days is my record and usually it's under ten. My main reason for mentioning them however is they have a new (to me anyway) line of brushless speed controllers for unbelievable prices under the brand name of Shark. I have no idea if they're any good or not but I intend to find out.

mfr02 04-11-2021 04:43 AM

Being an occasional customer of Cornwall, I agree. Postage from them to me is very reasonable, but then again, we are in the same country.
Just had a look on their site because a new range of anything is always interesting, but didn't see any "Shark" on the brushless ESC page.

acdii 04-11-2021 08:15 AM

For now the boat is still in the early stages, still have one chine left to glue in and then I can sand and sheet. In the mean time I will read ahead to the motor section, provided it has one and will use what is recommended now that I found some decent priced brushed ESC with reverse, I was thinking of using what I had on my shelf then forgot it could use a reverse function. This is my first boat, but not my first RC, I have nearly 2 dozen airplanes of various types I build and fly and was thinking of using something from my existing stash. .

Retiredat38 04-12-2021 12:40 AM


Originally Posted by mfr02 (Post 12672637)
Being an occasional customer of Cornwall, I agree. Postage from them to me is very reasonable, but then again, we are in the same country.
Just had a look on their site because a new range of anything is always interesting, but didn't see any "Shark" on the brushless ESC page.

Depending on my search phrase I get different results on their web site for speed controls. I think the Shark shows up when "ESC" is the search phrase. Or maybe "Brushless Speed Controls" or "Brushless ESC". I spent some time one day trying to get the MTronik brand to show up. But that is the only frustration I've had with their site. And I figure it has to do with us both using English! :)

I just checked and a search with "ESC" brings the Shark brand right up front. I also realized the brand is actually ZTW and Shark is the model. To early in the day to sort through that now. Anyway, here's a link to one of them: Shark ESC

Retiredat38 04-12-2021 12:48 AM


Originally Posted by acdii (Post 12672664)
For now the boat is still in the early stages, still have one chine left to glue in and then I can sand and sheet. In the mean time I will read ahead to the motor section, provided it has one and will use what is recommended now that I found some decent priced brushed ESC with reverse, I was thinking of using what I had on my shelf then forgot it could use a reverse function. This is my first boat, but not my first RC, I have nearly 2 dozen airplanes of various types I build and fly and was thinking of using something from my existing stash. .

Might be time to build a C-130 so you can use the reverse function. Just not in flight. :)

Boats make a nice change of pace. If scale you can get detail crazy few airplanes ever match. I find sailboats and submarines of particular interest.

acdii 04-12-2021 06:50 AM

Only thing is, it is easier to find a place to fly a plane, than to run a boat. I can walk to my back pasture to fly, but drive 20 minutes to my inlaws to boat.

Retiredat38 04-12-2021 06:10 PM


Originally Posted by acdii (Post 12672800)
Only thing is, it is easier to find a place to fly a plane, than to run a boat. I can walk to my back pasture to fly, but drive 20 minutes to my inlaws to boat.

And you're about 35 miles west of my wife's family.
But, boats don't fall under the FAA. :)
Most boats do not need an exceptionally large body of water to run in. I've run them on small ponds on golf courses before. The subs are quite happy in a swimming pool.
Maybe it's time to hang some floats on a plane?
And without prior knowledge I suspect were you to simply head out you'd find water long before you'd find a runway.
And every few years the 'J' class boats have their national regatta in Chicago. These sail boats run 100 inches long with 10 foot masts and weigh anywhere from 75 to 100 pounds. A sight to see.

Just yankin your chain! :)


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