Brushless motor help

[AssociatedParticipant @associated]

hi guys I know this has been covered times in the past and have read a article on motors I still not sure what kva rating I would need . Also the inrunner and outrunner I assume it's a inrunner I want but would also like to water cool it vial a coil around the motor .

The boat is of ply construction and is 26" long .

Thanks

[AssociatedParticipant @associated]

[Dave MilbournParticipant @davemilbourn48782]

I would suggest you read the thread by Harry Smith on his Sea Hornet, which sounds very similar to your model. **LINK**

In my opinion Harry tends to go for the hotter end of motor/prop/battery combinations but it's a good place to start!

Dave M

[AssociatedParticipant @associated]

Sorry Dave should explained a bit better , already got a motor all Installed in the twinkler . But been given a kit by a friend of mine , His dad unfortunately passed away and he has been clearing out his flat .

[Dodgy Geezer 1Participant @dodgygeezer1]

If you are trying to chose a suitable motor for a particular kit, it would help us to know the name of the kit…

 

Almost all kits come with some motor recommendations. Have you checked the instructions? 

Edited By Dodgy Geezer on 12/04/2016 13:53:57

[AssociatedParticipant @associated]

It's the river police launch by vintage model boats .

Like a bit of speed but not ott, thanks

[Malcolm FraryParticipant @malcolmfrary95515]

With any brushless motor, inrunner or outrunner, it isn't the rotating bit that needs cooling, it is the static bit with the coils on it. With an inrunner, a coil works because the coils are outside, but for an outrunner a flat plate added to the motor mount does the job just as well. OTOH if the right combination of motor and prop is fitted, no cooling should be needed unless there is a strong, if irrational, need to have a source of potential leaks into the hull.

[AssociatedParticipant @associated]

Malcolm I'm not sure which a in runner or out runner is but surely a coil type cooling would be suitable for both ? How do I calculate what size propeller to use to not cause motor to get too hot ? Is it critical to cool a brushless motor ?

Been doing a bit of reading would this motor be suitable ?

**LINK**

Matt

[Dodgy Geezer 1Participant @dodgygeezer1]

An inrunner motor is physically like a brushed motor.
An outrunner had the outer case rotating with the shaft.This means that you cannot put a coil around it.

Inrunner usually rotate very fast indeed, and are good for racing boats. Outrunner run slower with more torque, and are usually better for sports boats like yours. The one you have picked is an outrunner.

It looks good and powerful – perhaps too powerful, and certainly rather expensive for me.  I note it has a 5mm shaft –  I would tend to go with a 4mm shaft and a 4mm prop-shaft – perhaps  something like this, which should provide lively but not extreme performance:

http://rclife.co.uk/Brushless-Motors/Brushless-Outrunner-Motors/C3548-1100KV-Brushless-Outrunner-Motor?sort=p.price&order=ASC

Brushless motors are odd things – they have no brushes, and brushes tend to limit the power you can put into a motor. Without brushes, you can keep putting more and more power into a motor until it melts. So specifying the maximum power a brushless motor can develop depends rather a lot on the cooling you can provide.

Outrunners tend to cool themselves better than inrunners, and for most sports boats the trick is to run the motor at a sufficiently low power to mean that extra cooling is not needed. The motor you picked, for instance, can take around 40A at 15v – I'm guessing you might think of running it at 10A/7.2v?  100W should be fine for an Aerokits  River Police, though I would defer to the motor specialists for a better guess.  The motor you picked is 600W max – my other suggestion is 500W…

I would think you would not need to cool the motor if running at 7-10v.  Just make sure that it's in a reasonable-sized engine compartment, and perhaps allow a little ventilation? If you need to cool an outrunner, it's an odd exercise – the outside rotates and there's a small section which stays static and is used to clamp it to the motor mount. The motor mount itself is then cooled 

Edited By Dodgy Geezer on 12/04/2016 23:30:01

[Dodgy Geezer 1Participant @dodgygeezer1]

(Whoops! pressed return before I finished!)

If you want to see what outrunners with cooling look like – here's a video:

**LINK**

[AssociatedParticipant @associated]

Thanks a lot , makes more sense so I know unless sport / racing a outrunner it is . What size esc would I go for ?

If running at 3cell (11.1v) and do a bit of ohms law I come out with 45.04. Do I go with a 50 a esc ? Or do I go higher still ?

[AssociatedParticipant @associated]

Also do I have to go for a boat esc ? Or can I use a aircraft type at same rating does it need to be water cooled also ?

[ashley needhamParticipant @ashleyneedham69188]

A. That is a good question and one which depends on so many things that there is no easy answer. I would get an ESC rated above the motors advertised maximum current draw and then use a wattmeter on the boat to actually check the actual current consumption physically. You will not be able to calculate the current draw by using maths.

It is more likely that the ESC will be the thing that needs cooling if it is 40, 50 or even 60A. A fuse here is essential with such large currents. A wattmeter should be purchased straight away if tinkering with motors this powerful, and an array of props also will be required, two blade plastic S and X pitch will do nicely, to get the best speed/power consumption mix.

Ashley

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Associated on 13/04/2016 00:26:10:

Thanks a lot , makes more sense so I know unless sport / racing a outrunner it is . What size esc would I go for ?

If running at 3cell (11.1v) and do a bit of ohms law I come out with 45.04. Do I go with a 50 a esc ? Or do I go higher still ?

The short answer is that you get an esc which can take the amps you are going to draw.

The middle-length answer is that your amps draw depends on lots of things which are not precisely known, so people usually like to have a bit of extra clearance. And the cheaper the esc is, the more likely it is to not actually support its maximum claim…

The longer answer starts by talking about your actual expected amps draw. You have suggested a 3-cell lipo and 45A, which seems rather a lot to me. The figures given for your proposed motor choice are maximum figures using an air propeller – so they are pushing the motor limits (as has to be done for an aircraft) and expecting the motor to be in a strong downdraft of cooling air.

Boat modellers don't get the advantage of being given example figures – our usage is much more unpredictable. I would expect you to run this motor considerably down-rated – perhaps on a 7.2V NiMH pack drawing maybe 15A? You could always up the voltage later should you wish.

I tend to go for the 'cheap unreliable Chinese' escs and over-spec the unit to 60A or above – but you will find many on this forum singing the praises of better quality Western gear where 45A means that it will happily do 45A! One thing that may be useful is a watt-meter, which will tell you what you are ACTUALLY drawing rather than guessing…

Any brushless (non-sensored) esc will drive your motor. But aircraft escs won't have reverse. Do you want reverse?

Edited By Dodgy Geezer on 13/04/2016 09:03:08

[AssociatedParticipant @associated]

I was intending to run this on lipo but can go for 2 or 3 cell does not matter . When mentioned cheaper Chinese esc a friend of mine has used turnigy motors and esc with great success, I have some of there batteries and a charger with no problems either . But I take it I could use a aircraft esc? Only one way to find out !

Regarding watt meter and fuses . Where would the fuses go ? Between battery and esc I guess ? Is there any kind of watt meter I can get that's a smart type of meter that records watts pulling while in middle of the pond ? Even if you was to hold the boat at the side would this be acurate enough ?

Thanks

[Dave MilbournParticipant @davemilbourn48782]

This is a pretty small model [26"] and isn't a very fast planing hull. I think the 35mm motor suggested would be over the top. I'd personally use the same set-up I have in my Huntsman i.e. 2822/17T 1050kv motor and 30A Fusion Hawk marine ESC, but using a 2S LiPo instead of 3S. A 35mm S-type 2 blade prop would be a good place to start but, as Ashley says, if you lay in a stock of different sized plastic props you're not going to break the bank. If the model needs more speed then you can increase the voltage to 11.1v (a 3S LiPo).

I use this wattmeter – it will record maximum voltage and current during a run and goes up to 100A. http://www.4-max.co.uk/wattmeter-budget.htm

Dave M

Edited By Dave Milbourn on 13/04/2016 09:30:27

Edited By Dave Milbourn on 13/04/2016 09:31:50

[AssociatedParticipant @associated]

Briliant Dave ! Am I guessing the less kv on a motor the more torque and less speed it has ?

That's a good idea get a selection of plastic props . Does it matter what way I turn my motor as long the prop turns correct way ? As I know with a brushless you can wire them up anyway and just swap 2 wires over and should turn the other way ?

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Associated on 13/04/2016 09:33:33:

Briliant Dave ! Am I guessing the less kv on a motor the more torque and less speed it has ?

That's a good idea get a selection of plastic props . Does it matter what way I turn my motor as long the prop turns correct way ? As I know with a brushless you can wire them up anyway and just swap 2 wires over and should turn the other way ?

Are you asking if brushless motors have a 'preferred' direction of rotation? The answer is that they don't.

Brushed motors might have their brushes offset in some way for greater efficiency. But brushless motors have their commutation handled by the esc, and this can perform any offsetting necessary no matter which way the motor is turning…

[AssociatedParticipant @associated]

Not exactly I know you can switch rotations I meant is it best to have a clockwise or anti clockwise turning prop ?

Dave , what size was your huntsman?

[Dodgy Geezer 1Participant @dodgygeezer1]

Props can turn either way – there is no efficiency issue. I like mine to turn anti-clockwise viewed from the stern, because then drag tends to tighten up the standard thread while they are running.

Props unscrewing and falling off never used to be much of a problem when electric motors were generally low-powered. Nowadays the torque available is such that a rapid acceleration (or reverse!) can easily unscrew a prop. So lock-nuts on the prop have become much more common…

[Malcolm FraryParticipant @malcolmfrary95515]

Air ESCs rarely have reverse since planes rarely need to go in reverse. Truck ESCs usually have reverse, but often have a brake facility on the way to reverse. In a boat, reverse is the brakes and when you want to avoid denting a concrete bank, you want it in a hurry, no faffing about with brakes that only exist in theory.

[Dave MilbournParticipant @davemilbourn48782]

Dave , what size was your huntsman?

24" O/A [1/16 scale]. See Model Boats Jan and Feb 2016 for full plans etc.

[AssociatedParticipant @associated]

Nice model that is Dave .

Ah yes good point no reverse on planes so a marine esc it is then , uh there's a bank full reverse and should save my skin ! Guessing you don't need to set the brake on ? Just full reverse on program.

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Associated on 13/04/2016 11:37:41:

…….. there's a bank full reverse and should save my skin ! Guessing you don't need to set the brake on ? Just full reverse on program.

Select full reverse with no lock-nut on the prop and you could well hit the bank anyway because your prop might fall off!

Actually, many boats do perfectly well without reverse. Racing boats tend not to need it – fast sports boats can do without it – it's practically essential on displacement hulls, especially manoeuvring ones like tugs…

[AssociatedParticipant @associated]

Would this be a more suitable motor and esc ?

Fusion 2815/24 1100kv outrunner and hawk bl 30a speed controller

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