Model Boat Mayhem

Technical, Techniques, Hints, and Tips => BRUSHLESS Motors and Speed Controllers => Topic started by: Garabaldy on September 22, 2008, 12:21:07 pm

Title: Brushless motors help
Post by: Garabaldy on September 22, 2008, 12:21:07 pm
Well im about to buy some motors for the fireboat 39 as the hull is progressing and will be ready to recieve some hardware in a week or so.  I have changed my mind a couple of times about motors now, i have been advised that the graupner speed 600 would be better than my original choice which was torpedo850.  But after reading that brushless motors are more efficient and you can get longer run times i was wondering if this would be a better option?  Can anyone advise me of a reasonably priced brushless motor which would be of roughly equivilent power to the graupner speed 600 motor?
Title: Re: Brushless motors help
Post by: Sandy Calder on September 22, 2008, 01:43:54 pm
Hi Garabaldy,
The efficiency you get is dependent on the load you put on a motor.
You can get 50 to 60% on a brush motor if you fit the correct propellor.
    Consider the low speed characteristics your motor/esc gives to the boat.You may find what you might gain in motor efficiency is lost in the speed control so your duration of sail may not improve unless you throttle at 100% for the duration.
   I would never recommend a Torpedo 850 motor to any model boat user. Furthermore,if vendors and shopkeepers sat a technical exam on the relative merits of 800 and 850 motors then the 850 motor would be deleted.
Sandy Calder
Title: Re: Brushless motors help
Post by: Garabaldy on September 22, 2008, 02:26:08 pm
Thanks sandy,

I have a tendancy to go full throttle most of the time anyway.....  I have heard nothing but badness about the torpedo 850 motors!

Can anyone reccomend a brushless motor which would suit my needs?  To ensure i have a reasonably quick boat ;D   And i generally fancy getting into this brushless malarky, its all very interesting stuff.
Title: Re: Brushless motors help
Post by: nick_75au on September 23, 2008, 10:19:23 am
Might be able to help , can you point me in the right direction as to what the boat looks like and size etc.
Title: Re: Brushless motors help
Post by: Garabaldy on September 23, 2008, 11:58:51 am
nick_75, you have a pm
Title: Re: Brushless motors help
Post by: Tug on September 23, 2008, 09:14:11 pm
Nick, don't keep it all to yourself,, tell us all the gory details,
maybe someone has a rich uncle¿  Tug
Title: Re: Brushless motors help
Post by: Garabaldy on September 24, 2008, 12:39:52 am
Tugs right, i just passed the boat info over the pm....

Is there any word on a marine specific brushless motor hitting the market?  maybe there already is a range and i just havent seen it yet?  On some of the more powerfull brushless motors i notice you get around 300kv so if you run that on 12v you end up with a good speed for some tugging power.   Would this be a more efficient set up than a standard brushed motor with just as much if not more torque?  Allbeit an expensive alternative to a standard brushed but its still interesting.  Im just thinking out allowed here.  Hopefully im not the only person thinking these things...
Title: Re: Brushless motors help
Post by: nick_75au on September 24, 2008, 06:48:48 am
Hi Garabaldy,
I reckon that the setup that I use in the Springer will work well on 6 volts, If its not fast enough up the volts But watch the amps rise exponentially, I tried it once on 12 volts and it drew close to 15 amps lots of wash but being a springer tug not much faster.

My set up is a 1000 KV KA22-20L motor with a Pulso/X-power reversible speed control for boats,  40 mm Raboesh prop, it draws 3.5 amps holding the boat still and can tow our 11 foot rescue tinny. With your slippery hull It would move along quite nicely. You could go for a lower Kv motor for 12 volts .

The motor I have has spun a 75 MM prop but not recommended. the Speed control wouldn't drive it at low rpm and the current approached 30 amps.
If you put a larger than 45 - 50 mm prop on it I think the next size up usually 36 mm motor diameter would work, these would be closer to equivalent power of the 600 motor and will most likely be available in lower kv than the 28 mm diameter motor.

Browse through the Hobbycity website on the outrunners they have a massive selection.

Hope this is a start for you

Title: Re: Brushless motors help
Post by: Garabaldy on September 24, 2008, 08:33:24 am
Cheers nick,  this is good stuff.

1 motor i was looking at was this one > but i suppose it would probably be too quick on 12v, or is it more of a personal choice to speed?  When reading the current on brushless motors,  when it says 30amp, is this just what the electical contacts are rated to rather than what current the motor will actually pull?  Also if i used a 1000kv motor on 12v this would produce 12000rpm where as the graupner 600bb has a 17000 or somthing.  Wouldn't the graupner be faster or does the rpms on the graupner drop radicly when loaded?

Ohhhh so many questions, so much to know!

Thanks again,

Title: Re: Brushless motors help
Post by: nick_75au on September 24, 2008, 09:48:48 am
My motor is closest to the thumper 2830 motor, I think the 3648 would be good although if you load it with enough prop its equivalent to a .40 two stroke.
The motor will only draw what the load demands.

I think that the graupner will drop off fairly quickly from the no loaded speed, It still will be fast though :)

The thing I've found is the rpm doesnt drop much at all, the 75 mm prop although grossly overloaded still allowed the motor to spin at 2500 rpm from a theoretical 6000 rpm, the 40 mm prop drops the rpm by about 500.

There are some marine specific motors with water jackets out there but all are go fast types, there is a fella over on RC groups who has converted to brushless on his Mr Darby with 660 kv motors and 4:1 belt gearing.
there is also a Finnish fellow with similar kv (500) motors in a very fast patrol hull and 40mm waterjets only difference is the voltage.

Its all abit of a learning curve still. Some experimenting with voltage will be required I think.
Title: Re: Brushless motors help
Post by: Garabaldy on September 24, 2008, 10:24:19 am
i was also considering the 3530 as its cheaper although a slightly higher rpm.  I would probably be using a 45mm prop.   Il be ordering the motors in a couple of days so i can think about it some more.  How is your speed controller?  I did a quick search on google but couldnt find much.  I was looking at the mystery ones on ebay, they seem a reasonalbe price.  I also found a water cooled boat specific controller on ebay too which looked good.   

The only reason im opting for 12v is because i already have the batteries but i believe your right, some experimentation with voltages is a good idea.

Title: Re: Brushless motors help
Post by: Martin [Admin] on September 24, 2008, 11:24:33 am

At last we are getting some real information about Brushless Motor for use in model boats!  O0

This is the problem - Pick one from this lot!?!?!?

A few points to note: (and I stand to be corrected....)

Brushless motors need brushless speed controllers - you can't use normal DC ESC's, (Electronic Speed Controller).

Most brushless ESC are non reversing - Reversible and Reversing are NOT the same thing when reading the advert!

Brushless motors rev considerably higher than the "equivalent" brushed motor.

Brushless motors are "more efficient" than brushed motors but only when motor, load (prop) batteries, correctly balanced.

Brushless motors don't like to run slowly unless you have a "sonsored motor and controller" - which I understand to be
considerably more expensive that the "standard / non sensor" types we are discussing here.

Many brushless ESC can be "programed" and certain parameters (such as battery type) can be configured via the transmitter
or a special programming card.

Numbers game - This "lifted" from the Mtroniks site....
"Brushless motors are rated by either a number of turns or a 'KV' rating. 'KV' basically stands for rpm/volt, eg. A 2000KV
brushless motor when running a 7.2V battery would theoretically give (2000 x 7.2) = 14400rpm
The lower the number of turns, the more powerful the motor- The higher the KV rating, the more powerful the motor." (

As much as we want to, you can't take out your Speed600 etc, and pop in a brushless equivalent.... well yes you can but find
what motor is the "proper" equivalent is like defining a length of string. So far very few manufacturers or retailers have ventured
"This motor is equivalent to a Graupmer Speed600 at 12v" or "This motor will turn a 500mm 'scale' propeller in a displacement hull."
Closes I've seen so far (please include others you've seen...) are:

The SF 3000 is a 3000KV 400 can size 6 pole outrunner in a can that is perfect for use in light aircraft and especially
good when used together with Duct fan units. (

P2 features
Standard 540 can size and weight
User friendly solder tabs for easy and neat connection to the speed control
Re-buildable design to help keep the motor clean and running at highest possible performance
High performance, low friction ball bearings
Hardened 3.17mm motor shaft to match all existing standard pinions. (

Some listed on the Horizon Hobby site but no "equivalents" stated: (

Feigao 380 Size Motor in the "L" length for Micro Boats.
Product ID: fei-540S - Feigao 540 S Sized Brushless Motor
Product ID: fei-540L - Feigao 540 L Sized Brushless Motor
Product ID: fei-540XL - Feigao 540 XL Sized Brushless Motor
Product ID: dh-blcomboaq - AquaCraft Motor & Esc Power Package (

Powerful BRUSHLESS motor for model boats such as the B-28 and 20 cells. Suitable propeller approx. 42 to 45 mm Ø.
Identical fixing hole pattern to SPEED 600 motors: hole spacing 25 mm, 2 x M3 threaded holes. (

See also: ( (

Title: Re: Brushless motors help
Post by: nick_75au on September 24, 2008, 12:54:29 pm
About 70 % of brushless motors are not suitable for SCALE boats I think, rule out anything over 1500 Kv unless its a small fast boat. Ones designed for RC cars strike off the list immediately unless its a rock crawler motor. Scrub the ones that look like a curved metal bell (not enough torque). I would almost say scrub all inrunner motors unless its geared and watercooled( someone will pipe up about this one im sure ;D) FE is a completely different matter ;)

Most brushless ESC are non reversing - Reversible and Reversing are NOT the same thing when reading the advert![/font]

Brushless ecs with reverse, the top one is the same as the one I have.

Brushless motors rev considerably higher than the "equivalent" brushed motor.

it depends on the Kv of the motor, a lot of outrunner motors and some inrunners are able to direct drive without a gearbox
The rpms I've seen are from 120Kv to over 7000+ kv on 6 volts that means from 720 rpm to 42000+ rpm, outrunners can be physically much smaller than an equivelent power brushed for the same torque and not require a gear reduction.

My springer motor turns over at 500 rpm at lowest throttle, the ESC has to kick the motor for a second at a higher rpm to sense it rotating but will tick over the motor after the initial burst.

I sort of don't agree with the statement from mtronics, yes the higher kv has more power but the torque drops way off requiring the use of a gearbox. Low Kv means high torque which is what we want for our scale boats

I almost think its easier to select a brushless motor, example Raboesh 60 mm prop max rpms 5800 rpm, 12 volt system, 5800/12 = 480 Kv  or if a gear reduction is required multiply the kv by the ratio 2:1, 2*480 = 960 kv  obviously only needs to be ball park an 1100 kv would work fine.

3.5 amps compared to 6 amps, same kv motor brushed spec was 11500 at 12 volt so KV 960,  brushless motor supposed to be most efficient at 17 amps. Im fairly sure the brushless setup is efficient, it generates so little heat I don't even water-cool anything, the brushed motor needs cooling.

Im not an expert at brushless by a long shot just a lot of reading learning what the numbers mean  and jumping in with a couple of small setups.


Title: Re: Brushless motors help
Post by: Garabaldy on September 24, 2008, 01:20:52 pm
it was the sea king speed controllers i saw, its possible i wont need water cooled ones though i guess....

another good place to read about brushless is the pt boat site here

Title: Re: Brushless motors help
Post by: debssnal on October 01, 2008, 06:31:17 pm
 i would fit a Tornado Thumper 4250 Brushless motor - 720 watt motor, 600 kv. @£29.99 and a
this will give you more power than you running at scale speed you will get a long running will also have a lot more power for some fun running.also you can run a 50mm prop four can run on gel cel batterys ok as well.i have just put a brushless in a fishing boat and on 6v 7ah battery it ran for 3 1/2 hours on sunday. when i had the 600 eco brush motor in it i could only gat 1 hour running time
take a look at this
kind regards
Title: Re: Brushless motors help
Post by: Garabaldy on October 01, 2008, 07:02:38 pm
cheers debssnal but its too late - my motors arrived today!  I ended up getting the c3530 1100kv x 2 for 19.99 each.  heres hoping for a speedy boat!
Title: Re: Brushless motors help
Post by: debssnal on October 01, 2008, 09:46:17 pm
Hi no probs,let us no how you get on
kind regards
Title: Re: Brushless motors help
Post by: Martin [Admin] on October 03, 2008, 09:44:31 pm
Want a torquey, 'slow' brushless motor setup?
How deep are your pockets?

Title: Re: Brushless motors help
Post by: nick_75au on October 04, 2008, 12:27:24 pm
Neither of those motors are Torquey they are high RPM car motors that need a high ratio to work properly, just ask Toesupwa, with his Seahornet.
this is torque

Title: Re: Brushless motors help
Post by: Martin [Admin] on October 09, 2008, 11:24:04 am
Still not knowing anything about brushless motors but wishing to experiment, a search on fleabay for
Brushless + Truck + combo brings back some interesting results!

These are "standard" 540 size and listed as replacement motors for RC cars / trucks etc.
At lease I don't have to worry about "have I got the right ESC", "is this motor too hot or the right type", etc.
I know what a 540 motors is and these are "equivilents!"

It's a starting place , well for me anyway!
Title: Re: Brushless motors help
Post by: Garabaldy on October 09, 2008, 11:57:35 am
martin im no expert but when it says the same "size" as a standard 540 motor i believe it means physical size.  On that first motor/esc combo the motor has a kv rating of 4300 so if you ran 6v through it you would end up with excess of 25000rpm.  Of course it depends on the type of boat but i think for a scale boat 25000rpm is a little excessive unless you are gearing down of course.  Im personally not a fan of gearbox's as its making things a little complicated.  As Leonardo da Vinci said "Simplicity is the ultimate sophistication"  Of course i am learning here too and i stand to be corrected on this.   Im in the process of installing my motors in my boat at the moment and they have 1100kv rating.  They are tornado thumper motors.  As soon as i get some proper sea trials done i will do my best to report back in detai.  I have to say though, for the money i paid for them i am really impressed how they came.  They come in a proper plastic box with some kind of rubber composit cushion cut to fit the motor with spare connectors and allen key.  They are tiny!  Build quality seems far supperior to the last motors i bought (torpedo 800 for £25) so far im a happy modeller.  Im hoping my speed controllers will arrive in the post today too.

On one of the other forum theres extensive postings about brushless motors and brushless ESC but its mostly car heli and plane orientated.  Very little info on boats but its still interesting reading and helps with getting familiar with terminology/manufactures ect..

Would it be usefull if there was a brushless specific section on the forum to help make this area of model boating less grey?  Maybe it would help make people less fritened in a little brushless experimentation.  Im terrified my boats going to go up in smoke! haha

Title: Re: Brushless motors help
Post by: roycv on October 09, 2008, 01:31:16 pm
Hi all, The postage costs are a bit of a rip off.  I see one of the items was p&p £12 odd.
I paid £12  last year p&p (motor, gearbox and brushless ESC cost £6.82) and the jiffy bag came covered in stamps $15 worth.  It was only while I was in Hong Kong that I realised that the exchange rate was $15 to the pound.

I think they could still make a profit if given away and rely on the p&p charges.
The one I dealt with has since reduced their charges and are easy to find on ebay.
So watch out for the hidden costs.

No doubt they are produced in China.  I know of for instance a Security camera system that was on sale in A***S a while back for £149.00 that came into the country from China for under £20.00.
So you can assume that the seller in Hong Kong did not pay very much at all for the product he is selling.

regards and watch your backs!

Title: Re: Brushless motors help
Post by: Martin [Admin] on October 09, 2008, 01:54:04 pm

Roy: Yes your right about the postage on the eBay items but that the world we live in. Also the prices from any UK supplier (if there was actually one that knew anything about brushless motors in model boats) start at 3 times the eBay prices....

Gary: Yes, I should have stated, ' brushless for use in a sports, speed or race type boat'. I too hate the use of gearboxes.... nosiey, whiney, power hungry things.... USE THE RIGHT MOTOR!     ( Sits back and puts crash helmet on!  ;) )
Title: Re: Brushless motors help
Post by: andyn on October 09, 2008, 04:11:42 pm
If you wanted to go supersonic-like I'm sure Clever Trevor (code name ok2) at our club would have something.

Tornado Thumpers are very good motors, quite cheap too.

I very much reccomend Robotbirds. Superb service and cheap prices.

Motors: (

Title: Re: Brushless motors help
Post by: steamboatbob on October 10, 2008, 02:13:25 am
In my small knowledge the only way to get decent torque out of a brushless motor would be to use a gears to reduce the revs and thus increase the torque but i have not seen a setup for a geared brusless motor that i like.

Brushless motors are to be quite honest useless in a scale boat as they have high current draw so a high end ESC is required, even though they are very efficient they will drain a battery in no time flat. most people i know that run brushless setups dont get more than 15-20 mins out in one run at full power on a twin battery in parrallell.

i had a paddlesteamer that i ran on a 12v 7Ah Gell cell battery and it would run for 4-5 hours with lights, Smoke unit, and fog horn being used at the same time, but my new boat which i have run the motor a few times 5070 KV 6 turn Feigao 540L will run a 7.2V 4200mah battery down in around 8-10 mins

Yes Brushless are more efficient at using power but they have an extremely high current draw so most batteries do not last long. The motor i have to be placed in my Slo-Mo-Shun has a current draw listed at around 80-90 Amps. this means also that i will have to go for a lipo battery as nicd and nimh batteries will not cope with this type of current draw.
Title: Re: Brushless motors help
Post by: David_S on October 10, 2008, 05:44:04 am
To the best of my (also limited) knowledge, there is no reason for brushless motors to be more current-hungry than brushed motors, in fact the opposite, it is simply that the motors currently available are sold on the basis of their high power output, for the boat/car racer types and model fliers. I have two small brushless motors in a couple of planes, each appears externally identical, but on the same battery pack, one is a low-revving, torquey motor and the other is higher revving. Each is suited for its particular purpose. Perhaps there is simply not a strong enough demand for low-revving, efficient brushless motors for scale boats to make them a financially viable option for the manufacturers?

Having played a little with larger brushless motors a few years ago (in model planes that would take a glow engine of .40-.60), I can assure you that low kv brushless motors do exist, but that good ones are not cheap.
Title: Re: Brushless motors help
Post by: Garabaldy on October 10, 2008, 08:27:59 am
There are hundreds of low kv motoros out there but like david_s says they are not cheap.  going by memory the lowest kv i have seen is 380kv i think.  Steamboatbob did you read what nick_au said regarding his current draw in his springer?  I am hoping to get at least 40 minutes out of my set up using a 12v 7amp battery but time will tell.  Perhaps its a little early to be making bold statesments about brushless motors being useless in scale boats.  Or maybe i am just saying that as i have sunk a chunk of money into doing it!  My understanding of the high current draw which is stated in the brushless motor specs is not what the motor will draw all the time but more the max it will draw when loaded with the maximum size of prop(aero).  I am speculating more than i should so i'l stop.

If i get 40mins run time out of my set up i'l be happy :-)
Title: Re: Brushless motors help
Post by: steamboatbob on October 10, 2008, 09:31:19 am
the setup he is running sounds good 12v with a 1000kv motor will give you a 12000 rpm at the prop and running on a gell cell would give you a very good run time when measuring the current draw on my boats i use my biggest esc i have an old 50 amp from proboat that never goes wrong, i wack the multimeter on it and purchase a esc on the values i get but with brushless is the easy part go to the manufacturers home page and 90 percent of them will tell you what the current draw will be with no load then just try and factor in enough room for the power lower kv moters are good dont get me wrong on this but i just prefer to not to run them in a scale boat as our scale beasties do not need to be seen going quicker than the guys doing their lapsround the circuit lol

this is an article i found to be a very good read By Jay Turner;col1

these are some data sheets from feigao about their motors and you can see the various amp draw for each type of motor which should help you decide
just remember that the Kv rating is the revs per miniute per voltand you should be fine



Title: Re: Brushless motors help
Post by: nick_75au on October 10, 2008, 10:06:41 am
I run the Springer on 6 volts, still enough power to pull our 11 foot rescue dingy with man on board and 3.5 amps draw, motor specs say it draws 17 amps. Like I said the motor will only pull as much as asked of it.