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View Full Version : Opinion on using brushless motor (direct drive) on scale boat.



JCAustralia
12-08-2012, 10:17 AM
Hi guys

This is my latest addition to the fleet: Aquacraft Atlantic Tug.

I bought it during my visit to Hawaii and carried it all the way to Australia:biggrin:

Being a scale boat it has a brushed motor.

I was wondering whether I could use a brushless motor (1800 KV) and a 2s lipo that would give me about an RPM of 13000 max.

Being a scale boat I would probably use mainly quarter to half throttle for the scale drive.

Is it ok for a brushless motor to run at such low RPM?

I read in several post that it is better to run brushless motor at full throttle than at say half throttle....:confused1:

Thus I am also wondering whethere a brushless motor can be run safely at such low RPM with frequent acceleration and deceleration?

Thanks a lot.

srislash
12-08-2012, 10:26 AM
I believe the main issue is the ESC only running part throttle full time.My LHS has got some ESC's in from the UK, I believe, that are made for the scale community.I'll get the name of them when they open.This LHS specializes in the scale stuff and sponsors these guys.


http://www.youtube.com/watch?v=zjC6CdSt7yQ

siberianhusky
12-08-2012, 10:35 AM
I'm building a lobster boat, planning on running an outrunner about 800kv on 4s, figure if I use a cheap 450 sized one it shouldn't heat up much at all.
Might buy one of even lower KV at the same time, they are only about 15$. I want a low enough KV so I can have a good scale top speed at full throttle.
A larger can size will/should have more than enough torque at lower kv to turn a scale prop. I hope!
The props I'm looking at are all pretty low pitch, according to the scale boat guys you want a large diameter low pitch prop at low rpm for pulling power.
It's going to be my new rescue tow boat so I don't want it to go fast, going to mount a pole on the transom and tow a line with a grapple hook of some kind.

Southwest
12-08-2012, 11:54 AM
Thanks for the video!!!! That was really NEAT!!!!

mtbenjamin77
12-08-2012, 12:50 PM
I used a 2877 kv motor on 7.2V with a fan cooled car esc in the aqua tug and it worked great. The only problem was the motor is so low in the hull it was sitting in water most of the time which caused the bearings to rust and finally locked up. I built the tug for one of the guys at the lake who didn't maintain it very well and the motor mount is a pain to get to in that boat so the bearings were never oiled. It was used as a recovery boat which put a good load on the motor. The ESC was a 35amp car from hobbypartz about $35.

Doby
12-08-2012, 12:57 PM
I use a pair of 9XLs on 3S in one of my scale boats with 2 Turnigy 120's with no issues.

srislash
12-08-2012, 08:46 PM
And these are the guys I was talking about http://www.mtroniks.net/details1.asp/ProductID/740/sid/1/g2hydra50.htm

JCAustralia
12-09-2012, 07:59 AM
Thanks.

Looks like you all had positive experience : )

Its just that i keep reading in some old posts that brushless need to be run at full throttle for max efficiency....

Hope its allright with less than full throttle and reverse.....

I am considering buying a car esc for my tug, use one of the FE motor lying around and a 2s lipo. Any opinion?

Thanks

JC

srislash
12-09-2012, 01:05 PM
Just use a cooling fan(a good one) and you should be fine.I use a Traxxas' in my little NQD jet.The small VXL ESC gets hot but the normal VXL3s is fine with no fan.It is just a 380 can size motor so not too hard on things.

lenny
12-09-2012, 02:07 PM
Hi,:tiphat:
You could also use a water pump of some kind,
To run water to the motor and esc.
If using a outrunner motor, Use a water cooled motor mount to help keep it cool.
The outrunner can handle temps in the 160f to 200f rang with no problems.

tsenecal
12-10-2012, 11:32 PM
being a tugboat, you want the max rpm of the propeller to be about 4000-5000rpm. I would buy an outrunner of 40-45mm diameter and 400-600kvm, with an esc with forward and reverse, rated for 35-45amps and then you will be able to run the boat at a scale speed without killing the ESC.

something like this:
http://www.hobbyking.com/hobbyking/store/__14740__Turnigy_L3040A_480G_Brushless_Motor.html

and this:
http://www.hobbyking.com/hobbyking/store/__7377__Turnigy_Marine_35A_Brushless_Boat_ESC.html

don't worry about the amps, at 7.4 volts, you will be lucky if you pull more than 10 amps at full throttle. you will, however want/need reverse, and the ability to remove the brake function/neutral bump... you will want to be able to slam from forward to reverse without having to sit in neutral.

in all honesty, the biggest problem you will have is getting a universal joint to go from the larger diameter motor shaft to the original propshaft...

for that, go here:
http://www.cornwallmodelboats.co.uk/acatalog/couplings-modular.html

and build it from the three pieces C8000 and C8008 and C80-- for whatever size the propshaft is.