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[Manfjourde]

I'm building a fairey swordsman and am going to go brushless in it. Thinking a 540 can and 26-3500kv with 2s lipos. What amp rating should I be looking for on ESCs? I have a 25a available that I'd like to use but think it may be on the wimpy side. Thanks! Ill try to get some pics up soon, I am bad at documenting my builds.

[Martin (Admin)]

 Yes, I would say 25amp is pushing the limits, aim nearer 50 but if you can afford to loose the 25's, try them out first! Use fuses!

[Manfjourde]

Thanks. I guess it depends in the motor too. Would a brushless 380 be enough to push this boat?

[triumphjon]

think we could do with a little more information , size of boat etc in order for recomendations for motor .

[Manfjourde]

It's essentially this boat, these are the plans I am using and following what bluebird did to build as well. It is 24" long, made from light-ply 3mm and birch ply 1.5mm. Other than that I don't know what else to say. I don't want to deck it out with a bunch of hardware, seats, etc. Just get it on the water and play.

http://www.modelboatmayhem.co.uk/forum/index.php/topic,9791.0.html
http://www.modelboatmayhem.co.uk/forum/index.php/topic,7668.0.html

[pompebled]

Hi Manfjourde,

With a hull that size, aim for about 10.000 rpm under load, to avoid having to run ridiculously small props and have a disappointing performance.

A brushless motor with 2600 - 3500Kv on 2S will give you way more revs than is sensible...
You'd have to run less than half throttle all the time, which will cause both motor and ESC to overheat and die, watercooling won't help.

In my M.A.S., roughly half the size of your Swordsman, I'm running an 800Kv outrunner on 4S, the 10.000 rpm under load propells it over 50 km/h....
http://www.modelboatmayhem.co.uk/forum/index.php/topic,34033.0.html

Please do consider a lower Kv motor.

If you go for a sufficiently large ESC, you'll get away with out having to watercool it, depending on your motorchoice and speedwishes, a 25A ESC even watercooled may be pushing it.

Regards, Jan.

[inertia]

In my M.A.S., roughly half the size of your Swordsman

Sorry. Can't argue about brushless motors but your MAS is 75cm while the particular Swordsman being built is only about 60cm.
The prototype had a 540 brushed motor running on 7.2v at about 12,000 RPM with no load and a 3-blade 35mm brass prop.
DM

[pompebled]

Hi DM,

If you take the time to read the entire topic I linked to, you'll see the 75 cm is my test hull ( prototype) and the build log is about the 110 cm version (with the brushless outrunner)...

The 12.000 rpm on a brass threeblade prop sounds about right, under load that's the 10.000 you should be aiming for.
On 3S a 1000Kv motor would be the ticket, on 2S that would be a 1500Kv motor.

Regards, Jan.

[Manfjourde]

Thanks for the input - I think I may go with a 1500-2000 for a bit more pep. Would a 380 size be fine? A guy on YouTube has a 25a esc with a 3900 kv and his swordsman goes well

[pompebled]

Hi Manfjourde,

I assume you mean this video:
http://www.youtube.com/watch?v=CJQuwqAi-gA
The set-up mentioned is a compilation of mismatches...:
Leopard brushless motor 3900KV, Hobbywing EZrun 25amp ESC, 7.2v NIMH 2000mah, M4 35mm sports prop.
- the only Leopard motor I can find with 3900Kv is this one:
http://www.ebay.com/itm/ePacket-to-USA-Leopard-RC-540-3650-3900KV-4-Poles-Brushless-Motor-for-Car-Boat-/281013315896?pt=Radio_Control_Parts_Accessories&hash=item416db2e938
It's rather big (overkill springs to mind...) for the boat in the video.
Its rated at 1300W, thats a decent motor for a 80 cm surface piercing drive monohull (not competition material, as the can is too short, but very fast).
- On 7,2V NiMH 2000mAh that would mean a max ampdraw of 180A.
No way a NiMH pack can deliver that kind of current, the result is in the video, the motor is severely bogged down due to the limitation of the NiMH, which are struggling to keep the motor running.
At the end of the video, you seen the ESC cutting off, as the batteries are fully depleted (and hot!).

The 25A ESC only survives, because the NiMH can't deliver the current the motor will try to draw.
Put in a Lipo packet that cán deliver and the ESC will go up in smoke.

The prop is no match for the Leopard, hence the modest speed.

To be honest, a 3900Kv motor on 2S gives you the rather ridiculous 25.000 rpm under load, that's a blender...

If the 380 size is an outrunner, you'll have plenty of 'pep'. An Inrunner that size only has a tiny rotor and relies on revs, in stead of torque.

Gearing down 2:1 would allow for a 'normal'(=efficient) size prop without overloading the (high revving) motor.

Too much revs on a submerged prop only results in cavitation (foam) without the matching speed.
If the prop eventually does bite, the boat will ride so high, it'll topple from side to side, or (most likely) run on the right side and half the bottom due to the torque of the prop.

Needles to say controlling it will be a gamble at best...

Regards, Jan.

[Manfjourde]

Thank you for the advice and help - being new to boats this is all good! So for model runabout sport boats is the 10,000 rpm a good standard to go for?

The motors I plan to use are in runners so I may need a 540 and bigger esc.

Here is the video link
http://youtu.be/CJQuwqAi-gA

I like the speed of the boat in the video, being able to go a bit quicker at times would be perfect.

[pompebled]

So for model runabout sport boats is the 10,000 rpm a good standard to go for?

Hi Manfjourde,

Yes it is, that's why I mentioned it.

Regarding your wish to use an inrunner; the motors that size are completely overkill when you look at the power required for a model your size.

A 24" Deep Vee with a submerged prop runs perfectly 'scalish' with a Speed 600 motor on 6 cells NiMH sub-C.
This motor puts out between 150 and 200W, depending on the model selected.

For the sake of argument, you're going for a 540 size brushless like this:
http://www.hobbyking.com/hobbyking/store/__17735__XK3674_1650KV_Brushless_Inrunner.html
This fourpole inrunner is capable of delivering over four times the power required to run the boat!
Granted, on 2S Lipo you're in the sweetspot with about 11.000 rpm under load, but the weight of that motor will upset the balance of the boat, as it's more than 100 gr heavier than an average Speed 600.

Running on the lighter Lipo's you'll need to adjust the layout to get the CoG right, or the running attitude will suffer (badly).

Such a Ø36 mm motor is completely overkill in my opinion.

The problem is the  fact that there are very few low Kv inrunners available which have a sensible power output.
This Emax is one I have tested myself:
http://www.bidproduct.com/more/cartview.php?id=7312
It's a two pole and runs nicely on 2-4S.
Again weight is an issue.

An alternative would be an outrunner, lighter, available in the desired Kv range and still immensely powerfull.
As an example of what not to buy:
http://www.bidproduct.com/part/Product_view_BRUSHLESS%20MOTOR_396.html
Running on 3S and a 42K prop in surface piercing set-up this motor makes my 65 cm ARPRO run over 55 km/h.
Not the kind of power you would want in your scale Swordsman, as the torque may flip it when full throttle is applied.

Something like this is going to work much better:
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8505
A Ø 35 mm can for sufficient torque and not ridiculously overpowered for this type of hull, still, be carefull with going full throttle.

Realistically you should also get away (fast) with something like this in the 1860Kv version on 2S:
http://www.bidproduct.com/part/Product_view_BRUSHLESS%20MOTOR_394.html

The smaller Ø motor makes for a shallower propshaft angle, which gives you a better running attitude.

Confused, baffled?

Keep the questions coming.

Regards, Jan.

[Subculture]

A 540 brushless moor will be no heavier and usually a bit lighter than a brushed version. The motor you linked to is more the kind of motor for a 1/8th scale car, with gob loads of torque and low(ish) KV.

HK do a 21 turn 500 size inrunner, sensored- http://www.hobbyking.com/hobbyking/store/__21954__Turnigy_TrackStar_21_5T_Sensored_Brushless_Motor_1855KV.html

Weight is no greater than a 500 brushed motor, and that will swing a 40-45mm prop all day long on 2S. Partnered with their 60A sensored controller (which is great BTW) you will have excellent throttle control, every bit as good as a brushed equivalent.

http://www.hobbyking.com/hobbyking/store/__28375__Hobbyking_X_Car_60A_Brushless_Car_ESC_sensored_sensorless_.html

[pompebled]

Hi Sub,

The reason I never considered a car motor/esc combo for a boat is because I mainly run fast electrics where car motors don't last very long due to overheating.

In a scale application, the motor and ESC you suggested should work very nice; if you don't overprop, you may get away without watercooling of some sort.

To be on the safe side, I'd use a watercooled motormount, so at least some of the heat build up will be cooled away.

I tried getting away without cooling in my M.A.S., but had to add it, as the ESC would cut out due to overheating (but only after an hour and a half of partial throttle in the burning sun).

Regards, Jan.

[Subculture]

Not hard to add watercooling (always helps) just get a 540 coil , and fit it with a pick-up tube behind the prop blades, job done.

[Manfjourde]

Thanks for the good info and points on the motors and ESCs. My background is with cars so I was planning on a car motor with a boat esc. I am fascinated with water cooling as well so am planning on that.

My question is would a 380 size motor fit the bill? Something like this
http://www.hobbypartz.com/96m280-2848-1800kv-22t.html

[pompebled]

Hi Manfjourde,

That motor is a two pole, less torque and hotter running, this fourpole has more torque and runs cooler:
http://www.hobbyking.com/hobbyking/store/__17725__XK2845_B_2000kv_Brushless_Inrunner.html
It does need a cooling jacket, as there's no airflow in a quick boat.

Regards, Jan.

[Manfjourde]

Thanks for pointing that out - I was actually looking at that motor as well! One of the comments on it says water would get in the screws with a jacket - would I need a shorter jacket to keep water out if that's the case?

[pompebled]

Either that (= less cooling surface), or sealing the screw with a dab of silicone.

Regards, Jan.

[pompebled]

Hi Manfjourde,

With a 40 mm cooling jacket I don't see any leaking issues.
http://www.ebay.de/itm/Leopard-28mm-dia-Motor-Water-Cooling-Jacket-LB28WCJ-40MM-lenght-for-RC-Boat-/140918584076?pt=LH_DefaultDomain_0&hash=item20cf66f30c

I'm running a 3674 motor from the same series and I can fit a 65 cm jacket on it just fine, just make sure to put the jacket on from the smooth end of the can, to avoid damaging the O-rings when passing it over the screws...

Regards, Jan.

[Manfjourde]

Thanks again for the info and link! I'm out of town at the moment and will look into it a bit more when I return.