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Help finding the right brushless motor

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ERIC DODSWORTH 120/01/2020 08:18:33
5 forum posts
4 photos

I have just bought a second hand crash tender /launch type boat I was going to fit an mfa marlin brushed motor but have been told it might not be up to the job

So as the title suggests I am thinking of going brushless but only seem to be able to find silly high kva speed boat motors

My boat is 45 inches long single prop (55mm) haven't weighed it but it's not overly light any suggestions welcome

Malcolm Frary20/01/2020 09:08:41
895 forum posts

Googling for "1000kv brushless motor" gives lots of hits. Picking one with the right power characteristics out of the many is another story. As is picking the other half of the motor, the ESC.

Dave Milbourn20/01/2020 10:10:56
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4011 forum posts
282 photos

I'd be looking to fit something like this one, using a 6S LiPo pack and a 120A speed controller Leopard Brushless Motor

Dave M

Charles Oates20/01/2020 11:21:54
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570 forum posts
46 photos

If you put aerokits 46. Into the search box, you'll find a post from a couple of years ago where Harry Smith put a brushless into the same model. He mentions his choice of motors and props and they seem spot on to me. He posted

The brushless motors I have in stock are a D3548/4-1100kv 910 watts or the 3648-1450kv 1600 watts.

The post is worth a read.

Chas

ERIC DODSWORTH 121/01/2020 19:53:34
5 forum posts
4 photos

my boat is very similar to the aerokits the 6s might just turn it into a bit of a missile might try it on less cells first and see how it goes

boat2.jpgboat1.jpg

ashley needham22/01/2020 09:06:04
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6666 forum posts
160 photos

Eric. What batteries do you have available? And if buying new batteries (especially 4+s lipos) would you have a use for them in your other boats?

No one has more than 3s on the pond and some of the boats are large and fast.

The usual question....how fast do you want to go!!

55mm prop...of what style? Is there a motor fitted at the moment and if so have you tried it in the water to see how it goes? 

 

Ashley

Edited By ashley needham on 22/01/2020 09:07:47

ERIC DODSWORTH 122/01/2020 18:55:45
5 forum posts
4 photos

at the moment it is a bare shell i have some 3s 2200 from my aircraft that i can parallel or series up to mak a decent 3s or a weedy 6s i can do the same with some buggy pack 2s to give a decent 4s it has been suggested to give a decent level of perfomance as an ic it would have had a 10cc motor so i was trying to get a prop speed of 10-15,000 rpm it is just what size of motor would manage that

brushless tend to make there power at low revs on a big prop what we have found with aircraft is to ignore the watt rating and stick with kv rating and battery size

10cc is around 900 watts but if that comes with a shaft speed of 5000 rpm on a 70mm prop it's pretty useless

the answer to how fast is enough to get it onto the plane i dont want to get it right out of the water as i have always been told with my planes slightly over is better than under when it comes to power you can always throttle back

Malcolm Frary23/01/2020 09:40:55
895 forum posts

Prop diameter is only one parameter. Among may others, pitch is important in determining how much water is going to be moved and how far in a given time, and there is always going to be a trade off between speed and accelleration.

ashley needham23/01/2020 22:23:13
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6666 forum posts
160 photos

I will just throw this in.

my MFA Fantome (1200x300) goes well on two much derided 800 mfa units on 12v. Possibly 70 watts each? X50 props.

i would imagine if I used a 35mm outrunner of about 900-1000kv on 3s with the same prop and say 300watts it would go very nicely.

Ashley

ERIC DODSWORTH 123/02/2020 13:41:08
5 forum posts
4 photos

after a long wait for the weather went to the local tarn this morning armed with a few batteries and a bit of optimism the motor fitted was a 4250 800kv a 3s 4400 battery (2 2200 3s in parrallel) and a 4s 5000 was going to series the 3s batteries but 22oo just wouldnt give the amperage. The boat went almost scale like but was full chat nearly all the time try again next time with 6 cells it is going to take a bit of power to get a 14lb model onto the plane on the plus side it was very planted on the water not affected too much by the wind

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