Super Comet PT50, Need brushless suggestions and other thoughts - RC Groups
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May 21, 2017, 10:51 AM
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Gun Tech's Avatar
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Super Comet PT50, Need brushless suggestions and other thoughts


Okay, hopefully others that ride the short bus, will have some suggestions. By pure chance, I was at a friends house and even though I have admired the overwhelming diversity of RC boats he has, I was shocked to see a PT50 hanging from the rafters. As I have taken an unhealthy interest in the concept of hydrofoils, I inquired if he would part with it. He graciously was willing to sell it to me for a fair price as it is missing the front foil. The struts are still present and I fabricated a quick prototype, but will probably make another one.

However, the purpose of this thread is to inquire if any other owners, have practical experience with suitable motor/prop replacements. This one lacks a motor, the shaft is bent at the end and will need replacement and the propeller looks almost suitable for a fishing trawler. After quite a bit of digging, the obvious weak link in hydrofoils is weight, power and run time on the foils. I have never played with brushless motors, but they seem to be the best option for efficiency. Could anyone recommend a good choice for a brushless motor and would one of the modern "racing" props be more suitable to this type of boat? I am not looking for blinding speed, but would like a solid setup that provides a moderately good run time on the foils to showcase the design. I realize that there are other factors such as battery weight, ballast location and proper curvature to the foils to get one of these to run well and I don't expect results without some work to refine it. I already have narrowed down the fact that these were originally equipped with a 540 Mabuchi motor at somewhere in the 14,000-17,000rpm range and a 2200KV motor would be about the equivalent in brushless. Other than that, I don't know the first thing about brushless motors and would appreciate some guidance. Thoughts on replacing the propeller would be appreciated.
Thanks

Mark
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May 21, 2017, 11:20 AM
Sea Dragon-Lover
Umi_Ryuzuki's Avatar
I think you are already on the right track matching the RPM of the original Mabuchi.
The PT50s ran well as originally configured. Replacing the shaft seems to be your most critical issue.



Below are the only photos I have archived that shows the forward foil of a PT50.

.
Last edited by Umi_Ryuzuki; May 21, 2017 at 11:29 AM.
May 21, 2017, 01:51 PM
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Gun Tech's Avatar
Umi,
Thanks, for the input. Brushless motors are uncharted territory and I hope I can come up with a good match. I'll be interested to hear any thoughts on a different prop.

Mark
May 21, 2017, 07:06 PM
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Gun Tech's Avatar
As is standard interwebs protocol. It doesn't exist without pictures, so here we go.

Mark
May 21, 2017, 08:13 PM
boat butcher
the goon's Avatar
.

Mark
May 21, 2017, 09:43 PM
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Gravman's Avatar
Nice hydrofoil. What a great find. I noticed that there are no intermediate supporting struts on the shaft. Looks about the same size as the S8.
May 21, 2017, 10:34 PM
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Gun Tech's Avatar
Gravman,
Thanks for the compliment. I was amazed that it had been there hanging above my head on many previous visits and I never noticed it. The lack of the front foil did hide its heritage a bit, so that is my defense for my ignorance (and I'm sticking to it! LOL). It turns out he has a couple of other hydrofoils that are Radio Shack type toys that he drags out on rare occasions. He bought the PT-50 hoping to fix it up, but never got to it and figures I will be able to make the new foil and get it running so that's why he was willing to let me buy it. As for size, it's about 24" long with about a 5" beam and weighs 2-3lbs with no guts in it. I did find a gent in Germany that has a 1/25 scale VS-8 hull, deck and foils. Not cheap, but I might look into it further for a rainy day project. If I get more info, I'll share it here. Hopefully I'll get some more info during the week from a friend I work with that knows more about brushless stuff.

Mark
May 21, 2017, 10:50 PM
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Gravman's Avatar
Thanks Mark, please keep us informed on what you do on this build. The S8 is slightly larger so I am thinking perhaps what you use could be adapted for use on my model.
May 23, 2017, 10:45 AM
Registered User
The one thing about this type of surface piercing foil design is that you have to make sure you do not over power the design. Along with the increase of speed with this type of design is also an increase in lift of the fixed foils. This will lead to the hull becoming unbalanced and harder to control to the point that is will flop over on her side.

This is one of the reasons the foil borne craft have gone to fully submersible foil designs with computer/gyro trims which allow much greater control at much higher speeds.

Once the hull becomes foil borne you do not want to go to much more in speed without having problems.
May 23, 2017, 11:32 AM
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Gun Tech's Avatar
Frank,
I have seen that issue raised and realize I can't go nuts for power. I have found a unique brushless motor design called a Tazer Twin that incorporates the ESC into a single unit. It is identified as a 540 series replacement and only slightly higher RPM. I realize that a combo design leaves the potential for having to replace the whole unit if a failure occurs, but the reduction in bulk and complexity seems like a good match for this application. If I give it a whirl and it works out, it might turn out to be a good match for others looking to explore a brushless upgrade. If the efficiency of a brushless can optimize power consumption, then the use of a li-po battery may offer capacity and weight savings to allow a decent run time on the foils. Oh well, we'll see what experimentation gets us. What's the worst that could happen..... Never mind, don't answer that.

Mark
Last edited by Gun Tech; May 26, 2017 at 11:29 AM.
May 26, 2017, 11:01 AM
Sea Dragon-Lover
Umi_Ryuzuki's Avatar
Worst case scenario is that it makes a good blender for cool drinks pond side.

May 26, 2017, 11:27 AM
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Gun Tech's Avatar
Umi,
Bingo! If it fails as a hydrofoil, it can be a win as food processor As an update, a friend of mine was visiting last night and I was showing the PT-50 to him along with my brass prototype foil. He then asked if I wanted one out of tempered aluminum and reminded me that he works in an aircraft sheet-metal shop. So after a bit of discussion, he's going to form another one for me to tinker with out of something a bit lighter. I just need to start ordering parts and get this sucker running. Once I get it in the water, I can start to sort out any handling/performance quirks. From what I have dredged up on the Interwebs, these models were fairly trouble free and user friendly unlike the limited other choices out there. Gotta love a challenge! In regards to that comment I had made about a 1/25 scale VS-8, I placed and order. I'll let you know more in a bit more than a month (4 weeks to produce and it's in Germany), I don't plan to build it for a while as I have quite a few other projects already lined up, but I can at least let others know more about it.

Mark
May 26, 2017, 02:33 PM
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Gravman's Avatar
Looking forward to seeing what you get from Germany.
May 26, 2017, 02:46 PM
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Gun Tech's Avatar
So will I. I estimated the weight of the parts without motors or electrical for the 1/25 VS-8 at a bit over 10lbs, so that one will definitely need some serious thought for propulsion and props. I'll use the PT-50 as a learning guide. Might swing by a hobby store today to see what they have in stock to start putting some parts in the PT-50 while I wait for the foil my buddy is making. The rest of the long weekend will be spent on bodywork for my 10" long battleship (USS California BB-44). I am almost done restoring the hull and then I can reinstall the motors and steering. Once that's done, I can regain some breathing room in my shop and work on smaller stuff.

Mark
May 26, 2017, 04:51 PM
Registered User
MARK- Am I reading it right that you are making a 10 battleship, or should it be a 10 battleship?


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