Brush to Brushless

[Bob Bighinatti]

I thought I saw a thread here some place on how to size brushed motors to brushless motors. I can not find it. I am looking to change out a 700 and a 550 motor to brushless with a little more power. Thanks .
Bob Big :) :)

[fgroza]

Bob,
Did you want to go inrunner or outrunner? Outrunners have the torque for scale, inrunners have the speed for direct/gearbox type of running. A 36mm inrunner is a replacement size for 550 type motors. However the KV of the motor has a bearing on the type of running you want. Amp draw, battery size/type also need to be addressed. Some people base what motor to use on watts needed/wanted for performance. In a fast electric for example, we usually stay around the 2000kv mark for the 36mm motors we run on 4 cell lipos. There are specs on mfg. sites that will help try to give you the info you need. As for the 700 size motor, try a large outrunner from Eflite or possibly a Feigo inrunner in the 45mm size. Ofshoreelectrics carry some large motors for boats. I'm not a expert on this matter, however this info is what we have used in the past with good results.
Frank

[Shaun Hendricks]

If you use watts as a standard, you need to look at the 'efficiency' of the watts. Brushless are far more efficient than brushed, it's not even a contest. The lowest separation I've seen is 10% efficiency and it goes way up from there.

So, look at the datasheet on the motors and pick a brushless motor with the same effective watts rating.

For example, if a brushed motor has 500 watts of power maximum handling capability at 50% efficiency, it's actually a 250 watt motor. If a brushless motor is 90% efficient then it only needs a maximum watt rating of 278 watts to match the shaft power of the 500 watt brushed motor.

That's just a 'rough' comparison but it's a decent place to start.

Simple truth is, the two motor types aren't perfectly comperable since they have internal strengths as well. Brushed motors tend to have a little better 'start' torque but chew up more juice to get it. Brushless motors are smoother in operation and don't 'slam' their speed controllers as bad as brushed do. Etc. etc.

Toss in outrunners and you have a whole new wrinkle to the mix. Throw in propeller options and you get the mess the boat side of the hobby is in right now. The aircraft guys have it down to a science, the boat side... not so much. Seems more art than science to me at this moment.

So, best idea is to put forward a good set of specs of the boat you are trying to propel and let the experts here give you an idea of where to start. Many are using brushless motors in scale and the FE field is dominated by them.

[Rex R]

the aquacraft super vee motor(1800kv) and proboat's blackjack motor(1500kv) are both a pretty good match for a 700sc. but at half the weight. usually you need to consider what voltage you want to run and how many rpm, availible space is also an issue.

[pkboo]

Bob, inrunners are more easily cooled than outrunners and like Frank says you get more revs out of an inrunner. If your motor is properly cooled (jacketed = inrunner) it will go all the revs (volts) you give it (rpm = volt * Kv) and you will need a higher amp ESC than what your internetshop recommends. The bigger the prop the more heat development, the higher the amp draw. Your batpack will suffer depending on the rpm/speed you want, brushed motors want their amps :p and fast :cool: I'm a starter of one "of the many" Shaun is talking about :D got three smokeless ESC to prove it :( ...!Boo

[Bob Bighinatti]

Well the 700 is going in a Monaco 100 with stright shaft with a 3 blade Octra437 prop about 42mm. The boat weights about 15 lbs without batts.
The Aristo-Craft 540 is going in a Miss Adventure that I am building at this time. It has a stock prop 3 blade at 1 inch . I looking at inrunners, with lipo's.
I hope this helps. And thanks for the help.
Bob Big :) :)
I will be using a 3s lpo 12volts. thanks . :) :)

[Rex R]

big boat(monaco) think I would go for a feigao 540 xl(36-74) 10t. hth
rex
edit
for the 'Miss Adventure' methinks a feigao 540 L (36-60) 12t would work nicely. I'm guessing that you would rather have a 'cool running' boat as opposed to some thing that can only run for 2 minutes before an extended cool down period.

[tigerbay]

A thought is running in my head. I am not an expert so could be wrong.

Do brushless motors may need a different type of ESC to brushed motors???

[gobigkahuna]

A thought is running in my head. I am not an expert so could be wrong.

Do brushless motors may need a different type of ESC to brushed motors???

They sure do. If you use brushless motors, you'll need an ESC designed for brushless motors.

[fgroza]

Bob,
As mentioned, the Fieago motors do the job at a good price. We run a 540XL 9 turn with the X437 3 blade prop on 4 cell 2200 lipos. We use 2 packs in series on a Blackjack cat. The price is around $70 for a 540 from Offshoreelectrics. You can get these motors in several different winds/KV ratings. Rule of thumb, lower wind, higher kv, smaller prop. Try to stay around the 2000 kv rating for your Monaco. I have a Mini EV in mine running the stock prop on 7 cell nimh packs. I also have a 10 cell pack I use on occasion. You should put a water jacket on whatever motor you use as it gets hot really fast without it. Proboat makes a nice water outlet fitting for a few bucks.
Frank

[Bob Bighinatti]

Thanks guys . Sorry i did not respond faster . I have ben without cable since
Friday due to an inc storm . Have a genrator running nonstop. Thanks agian.
Bob Big :) :)

[Bob Bighinatti]

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5145&Product_Name=TR_28-45_3600kv_Brushless_Inrunner_(WaterCooled)

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7360&Product_Name=Turnigy_Marine_60A_Brushless_Boat_ESC

Found these. What do you all think? It will be for my Monaco 100.
Bob Big :p :p

[Rex R]

motor: only if you don't mind running a tiny prop w/ a slow top end. just not big enough for such a large boat. the 700 series motor is rated at approx 420-480 watts...you'll be wanting about 550-650watts, and a kv rating of about 1800kv(for a 12v power supply)
edit
size 36-74 is the size I'd pick for that boat.

[Bob Bighinatti]

Thanks .
Bob Big :) :)