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Author Topic: Can a 5 brushless motor power a fast electric boat?  (Read 458 times)

Martin [Admin]

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Can a 5 brushless motor power a fast electric boat?
« on: August 14, 2020, 11:04:57 pm »


From Facebook:


https://www.facebook.com/photo.php?fbid=1737639643056030&set=pcb.1247612252243758&type=3&theater


Can a 5 brushless motor power a fast electric boat? - Neil McGrath‎

I was keen to find out so purchased one of these: https://www.banggood.com/Racerstar-BR2212-1800KV-2-4S-Brushless-Motor-For-RC-Models-p-1085434.html?rmmds=search&cur_warehouse=CN

I also picked up a 40A brushless controller for less than 10 from the same supplier. 
https://www.banggood.com/Double-Sides-Brushless-ESC-20-or-30-or-40-or-50-or-60-or-80A-Underwater-Thruster-RC-Car-Boat-Parts-p-1649988.html?rmmds=search&ID=516805&cur_warehouse=CN

My local boating lake is fairly small so I was not after mind blowing speed but would be happy to trot around at 15-20mph in my submerged drive deep vee.
The motor spec states that it should be capable of delivering over 200 watts at 11.1 v.  This would be much more power than I had  available in my fast electric racing days back in the 90s, so I had high hopes.
My battery of choice is a 2200mAH 3 cell pack which my local model shop is selling for just 11.99 and I predicted would provide about 5 minutes of run time.
The motor was mounted on an L shaped aluminium bracket with a U shaped aluminium tube attached to provide water cooling.
During the first trip to the lake the motor coupling could not take the strain and worked loose almost immediately.
On the second trip with a new coupling I managed about one fast lap before the same thing happened again (at least the motor has plenty of torque!).
I then invested in a collet style coupling, ground a flat onto the motor shaft and used plenty of thread locking compound to secure the grub screw - success!
On the third trip to the lake I did a couple of slow laps then opened it up. The boat was immediately up on the plane and was certainly giving the local IC boats a good run for their money. After a few laps I brought the boat in to check everything was OK. It did smell a bit warm and if I licked my fingers before touching the motor there would be that distinctive sizzle as the spit instantly boiled on the surface.  The rest of the time at the lake was spent driving a couple of laps then allowing time for the motor to cool between runs. The ESC was getting quite warm but nowhere near as hot as the motor. The batteries stayed cool throughout the exercise.
With the final battery pack installed the boat was back shooting across the water but this time it was starting to stutter. It was then  dead in the water and had to be recovered. Back on dry land the ESC shrink wrap had split open and my time at the lake was over. 

After returning home, I ordered the 80amp version of the ESC then went out to the garage to dry off the boat. Once everything was dry I decided to see if there was any life left in the batteries. To my surprise, the motor burst back into life and everything was working perfectly. I was sure that the ESC was toast, but at least I can now carry out some further testing while I wait for the new one to arrive from China.   
After this test it was clear to me that the boat was over propped. I was using a 35mm plastic propeller that is really meant for surface drive. The motor cooling was also clearly inadequate. I have now fitted a water cooled motor mount from Prestwich models, which should do a better job than the old L bracket with a bit of aluminium pipe attached. The next test will be with a 29mm prop which I hope will allow the motor to spin more freely, draw less amps and help keep the temperature down.

Watch this space. I will let you know how I get on.



I picked up the test hull at a boot sale so I am not sure what it is. I think it was probably an RTR boat originally. I would be grateful if anyone can identify it. The brushless gear will easily fit in the smaller GT400 boat, so it should really be a pocket rocket! John Gaze can you suggest any KV/prop combinations that work well for you?








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RST

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Re: Can a 5 brushless motor power a fast electric boat?
« Reply #1 on: August 15, 2020, 12:07:28 am »

Interesting post.
For me it's a bit different though I'n not an FE guy:

I woud rather pay more for mail order through a UK distributor any day than order direct out of the country.  That said, I am biased -I tried ordering a good few things direct from far east over the last years and almost every single thing was faulty/fake/failed or broke etc.  It was a disaster and money lost most times.  Never ever knowingly doing it again!  I have no problem with products being made in far east -it's been that way for a LONG time but I know through work, cheap is quite obviously cheap for a reason and exceptions are there, but few and far between.

Our UK mail-order shops seem far superior compared to when I am in Europe and order from European suppliers.  Apart from the price being MUCH higher so far -most Eurpoean suppliers have not packaged items properly and I received damaged products.  Something I find much rarer here in the UK.

...I have no doubt a cheap chinese electronic R/C product will work, perhaps something more to judge it on is the ratio of folk who say they fail compared to they are OK?  The odds are certainly not stacked in cheap imports for modellers from what I see, but like I said in opening I would still rather buy one European product than a cheap import and have it burn out and have hassle or just buy again.
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zooma

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Re: Can a 5 brushless motor power a fast electric boat?
« Reply #2 on: August 15, 2020, 09:34:23 pm »

Hi Martin,


I use exactly the same motor mount as you have just bought in my Rapier where it successfully cools a much larger 3648-1450 motor  - and that is after the water has already passed through a 180amp SeaKing speed controller!


One note of caution though, is that the first one I bought was not water-tight (!) and unknown to me it was pumping water into my engine bay as the boat was happily charging around the club lake on its otherwise successful maiden voyage.


Before sending the boat out for the first time, hold onto it firmly and open the throttle wide open.  You will then be able to see if the mount has any leaks while it is still easy to recover and before any damage can be done.


It is also a good idea to check the water inlet and outlet nipples to make sure that they are tight and if they move at all, seal them with 24 hour Araldite on the screw threads whilst the mount is still dry.


My second mount (exactly the same again) has been OK, but I could not return my first faulty mount as the two epoxy side plates are stuck in the hull with 24 hour Araldite and then secured with chopped glass matting and resin!


For the price of a new replacement I was not going to have the the hassle of cutting out these side mounting plates - so I just bought another one!


It looks like you have had a good buy with your brushless motor - the water-cooled mount would have cost you more!


Stay safe.


Bob.






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chas

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Re: Can a 5 brushless motor power a fast electric boat?
« Reply #3 on: August 15, 2020, 11:51:32 pm »

No need to order from China, it's surprising what appears on the dreaded Amazon sometimes. I recently got 2 x2212 brushless motors with f/o 30 amp speed controllers for 22 euros. I wanted  something cheap and chearfull for an experiment. They arrived in 36 hours and work perfectly. Actually they seem identical to turnigy motors with a different label.
Chas

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Tug Fanatic

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Re: Can a 5 brushless motor power a fast electric boat?
« Reply #4 on: August 16, 2020, 08:03:43 am »

The Bangood Racestar br2212 motors have a good reputation. I have flown a 1400kv version & found it very good for the money

Cooling in model boats is always an issue. Aircraft have nice big cooling fans on the front and those holes in the front of the motor are there to let cooling air through the motor. In a boat they don't do much.

I am told that with outrunner brushless motors it is pretty useless considering the heat from any part of the motor that rotates - which is exactly where many modellers touch to judge motor temperature. The heat from an outrunner brushless motor disipates from the static parts which the coils are attached to, and to which you cooler is attached. Unfortunately the heat build up in the coils to damaging levels can be very rapid and if that excess heat spreads to the magnets then their performance deteriorates a little more each time and never recovers. It is important to keep your motors cool. The magnets used in high quality motors are generally made of material that will withstand higher temperatures than those of cheaper motors.

Given the above I always try and over specify my motors so that the amount of heat that I was trying to dissipate per gramme of motor was as low as possible. Arranging cooling is more expensive than buying a bigger motor although mounting on an aluminium plate will always, I think, be worthwhile. For model aircraft use I generally work on the basis of no more than 3 watts per gramme of motor weight but for general hobby model boat use I would prefer 2w/g. The 200W that your motor is rated for is a) a Chinese 200W and b) probably assuming good cooling. Personally I would say that, at 52g weight, it was a 160w motor in a model aircraft and a 75-100w motor is an unvented uncooled model boat.

I have no idea how efficient your cooling system is but I wait with interest to see if other modellers agree with me.
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imsinking

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Re: Can a 5 brushless motor power a fast electric boat?
« Reply #5 on: August 16, 2020, 09:26:12 am »

I use outrunners in my boats, for the torque, my solution to cooling is a small computer fan rotor , stripped out of its casing and drilled to need forcing over the splines on a hucco coupling , must be accurately drilled or there's vibration, there would be ways and means of attaching one to any coupling set up .

You could even put a complete fan assembly near the motor , their only 5 volts tho' .
Even constant flat out running barely get warm . . .
Bill
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Fastelectrics

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Re: Can a 5 brushless motor power a fast electric boat?
« Reply #6 on: August 23, 2020, 07:08:09 pm »

As the poster of the original piece on Facebook. I thought you may be interested to see how my brushless experiment has progressed.


Swapping to a 29mm prop and improving the water cooling has helped keep the motor and ESC cool.


Here is a video of the boat in action. It still need some trimming but the speed is great for such a low cost set-up. 


https://www.youtube.com/watch?v=Aqt-Pq3QHD4



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Martin [Admin]

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Re: Can a 5 brushless motor power a fast electric boat?
« Reply #7 on: August 23, 2020, 09:10:52 pm »

 
Great stuff! - Can you get the batteries any further forwards?
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Fastelectrics

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Re: Can a 5 brushless motor power a fast electric boat?
« Reply #8 on: August 23, 2020, 10:32:08 pm »

There is a bit of space in front of the motor but I would have to cut out some of the internal hull moulding to make it fit.
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