Technical, Techniques, Hints, and Tips > BRUSHLESS Motors and Speed Controllers

Brushless Herecy

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Shipmate60:
I have been watching with amusement the way brushless motors are set up in a model boat.
I am looking at this with a purely engineering bent.
As stated brushless motors are aprox 15% more efficient and require less maintenance. (I have been working with these motors being a lot larger for 20 yrs).
 Assuming the 15% efficiency gain why do tug outrunners need 100 amp plus ESC? A brushed motor would use a 20 amp ESC.
Most users use Lipo batteries which are expensive and light then add copious amounts of lead for ballast.
To me if the motors are more efficient then shouldnt the ESC's be a lower or the same rating.
It just doesnt seem to make sense for cost or efficiency.


Bob

Subculture:
Why do tug outrunners need 100 amp plus ESC?

They don't. Many marine modellers ludicrously over motor their boats. Aero modellers have a much better understanding generally, where weight is very important.

Most users use Lipo batteries which are expensive.

Depends where you buy them, but generally speaking they're now the cheapest form of battery, especially when you take into account cycle life and performance.

then add copious amounts of lead for ballast

Which can be placed in the best position to make the boat handle well. Rather than dictated by a big lump of a battery.

Shouldn't the ESC's be a lower or the same rating.

Yes. But beware of inflated specs.

canabus:
Hi All
Many years ago I was using the standard wet cell batteries in a boat but changing to gel cell it fitted into the boat better.
Yes I had to add more lead but with the weight lower in the boat the handling improved greatly.
The same thing today the lipo batteries put out more power and are lighter.
As for brushless motor for the size they are far more powerful than the brush motors.
EG. a 540 motor 35mm is general about 90 Watts and in brushless motors can be up to 2000Watts.
All my boats are running brushless motor which are cheaper than brush motors.
The Lipo batteries are a bit dearer, so it balances out.
My cordless drills the batteries die and I replace them with Lipo batteries.
I found running the brush motors on Lipo's work very well and a lot longer between recharging.
Canabus

JimG:
Why use a an esc with a current rating much higher than needed?
In my case it was only slightly more expensive, I had used one in a fast boat and found that it had good slow running control, not all lower current escs do. I had a programming box for it so could easily program it to adjust the motor power to suit the boat. (Motor more powerful than needed but I already had one so more than made up for the extra cost of the esc.)

Jim

Shipmate60:
I can understand the use of brushless in fast boats but I still don't understand the need for huge ESC's and Lipos (the chargers are far more expensive) in scale boats or tugs.
My large tugs have large batteries which double as ballast, yes in the right place and run all day.
It still seems an anathma for the change. Not a dinosaur just don't understand the boat modellers way of using them.


Bob

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