Super Comet PT50, Need brushless suggestions and other thoughts - Page 2 - RC Groups
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May 26, 2017, 04:58 PM
Sea Dragon-Lover
Umi_Ryuzuki's Avatar
Quote:
Originally Posted by frankg
MARK- Am I reading it right that you are making a 10 battleship, or should it be a 10 battleship?
Both are possible...
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May 26, 2017, 05:45 PM
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Gun Tech's Avatar
Fat finger oops. Yes, that was supposed to be 10 feet.

Mark
Jun 08, 2017, 11:05 AM
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Gun Tech's Avatar
Well, after forming a curve, bending, drilling and riveting, we have a front foil! It's rough and a bit longer than it should be, but I can fine tune it if it looks like I am in the ballpark for lift. I wound up getting a Team Orion 540 brushless with the integral ESC, the size is perfect and keeps thing tidy, but I have some concerns about heat in the original plastic motor cradle. I probably will machine a brace out of aluminum and eliminate the plastic. This is getting interesting!

Mark
Jun 08, 2017, 11:28 AM
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Gravman's Avatar
Cool! Looking forward to the test run. How about a photo of the motor and mount?
Jun 08, 2017, 11:45 AM
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Gun Tech's Avatar
I'll try to take some pictures this weekend. I'm bad at documenting things while I do them, so I constantly have to remind myself that other people like to see "in progress" The original motor cradle is perfectly aligned when the motor sits in it, but after running the motor on the bench for 5 minutes with no load, I just don't feel like taking a chance at turning it into a molten blob. I'll figure out the height and angle then machine an "L" bracket with the necessary angle for alignment with the prop-shaft. That way the body of the motor will be suspended and allow better cooling. There is a small access port right above the motor and I may add an exhaust fan to promote airflow through the hull and around the motor. If all goes well, I might have it in the water in about a week and a half. A buddy of mine allowed me to raid his parts box for a selection of propellers for speed boats, so I have to sort through and see what will work best.. We both agree the original prop is ill suited for what this boat is designed for, so hopefully I'll wind up with something better matched for less blade in the water at full speed.

Mark
Jun 10, 2017, 06:50 AM
Boaters are nice people.
Quote:
Originally Posted by Gun Tech
after running the motor on the bench for 5 minutes with no load, I just don't feel like taking a chance at turning it into a molten blob.
Hi Mark,

Please read up on brushless motors and what you can and can't to with/to them...
Running it for a longer period of time on the bench without load, is not done, as things will heat up rapidly, as you'll have noticed.

This has to do with the fact that the ESC has to do a lot of switching at partial throttle (I assume you didn't run it full blast for 5 minutes?), which tends to heat up both ESC and motor.
As they are one unit in your case, the heating up will even go quicker.

Is this the motor/ESC combo you're talking about?
http://www.ebay.com/itm/Kyosho-1-10-...-/401049024981

Be aware of the fact this is a motor designed for a car, working on a geared down transmission.
In my experience car motors have to be used with care in boats, as they can't deliver the torque required to turn a decent size prop, they tend to overheat and die.

Apart from that, an appropriate outrunner with a seperate ESC can be purchased for a lot less...

Regards, Jan.
Jun 10, 2017, 08:30 AM
Registered User
Gun Tech's Avatar
Jan,
I appreciate the input. When I said 5 minutes that was push the throttle forward to the stop and let it run, it was a battery test, not a motor test. It didn't get dangerous hot, about hot car in the sun level. You could handle it, but holding it was a bit less than comfortable. As for power, this motor is pegged as a brushless upgrade for applications with 540 motors. Spinning the original 37mm prop or one slightly smaller plastic replacement better not pose an issue, since I have other boats with smaller can motors spinning big brass props direct drive and high rpm. Outrunners just have too much diameter to nestle down in the hull for alignment with the prop shaft. I realize that I could use a pulley setup to offset, but for the moment we'll stick with simplicity. It's going together this weekend and should be ready to test soon. And yes, that is the model I got for a motor.

Mark
Jun 10, 2017, 03:46 PM
Boaters are nice people.
Hi Mark,

I have never seen a PT50 in the flesh, but I imagine the motor is held in a vacuum formed plastic cradle of some sort.
This makes the use of an outrunner a 'challenge', to put it mildly, as the outside can of this type of motor turns.

A 36 mm motor should be a direct drop in, but you'd have no way of watercooling it, which for the majority of brushless inrunners is a must, to avoid overheating.

A watercooling jacket around a 36 mm motor would increase the to about 42 mm, which would mean modification to the motormount.

An outrunner is mounted on a bulkhead style mount and would also mean mofifying the existing cradle.

Let us know how the testruns work out.

Regards, Jan.
Jun 10, 2017, 06:25 PM
Registered User
Gun Tech's Avatar
It's mounted and water tested, courtesy of the wife's fountain in the back yard. Water cooling is unfortunately not an option, but this motor is for 1/10 scale cars and they manage on air alone, so I'll see what happens. I have to retract my original statement that the prop was a simplistic design. When I held the stern in the water and applied power, I was a bit shocked how much thrust it produced. Under a brief full power run, I would say it was well over 5lbs of force. I'm going to get a servo in it and try to test it Monday since I have a weekday off to play.

Mark
Jun 11, 2017, 06:55 PM
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Gun Tech's Avatar
Crappy one handed camera work, but it has taken flight! Took very little practice to figure out where the power was matched for a steady run. I even tried a few passes at full throttle. Conditions were very windy, but she was very well behaved. I hope that this video will show up.
https://www.facebook.com/mark.shaw.7...4133489340365/


Mark
Jun 12, 2017, 12:08 PM
Sea Dragon-Lover
Umi_Ryuzuki's Avatar
No video,...


Please stand by

Blues Brothers - elevator music (2 min 42 sec)
Jun 12, 2017, 05:12 PM
Registered User
Gun Tech's Avatar
Sorry about that. It was a Facebook post. Here is a second video from today on YouTube.

Second run with the PT-50 Hydrofoil (1 min 18 sec)


Mark
Jun 12, 2017, 06:58 PM
Registered User
Gravman's Avatar
Man that is really neat! She runs great!
Jun 13, 2017, 08:52 AM
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Gun Tech's Avatar
Thanks, I wound up taking the plunge and bought a pair of 5200mah 2S Lipo's with a charger. The two of them weigh the same as the Nimh battery and they snuggle right into the hull between the bulkheads. Hopefully, I will get a chance to run again this weekend.

Mark
Jun 13, 2017, 09:22 AM
Registered User
Gravman's Avatar
I have been reluctant to go with the LiPo batteries. You hear a lot of horror stories about those packs. Mostly from operator error. I am prone to duffusoidal tendencies and you have to have your mind on the game to use those packs.


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