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Author Topic: RoMarin/Robbe/Krick Najade Brushless set up question  (Read 174 times)

davejay

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RoMarin/Robbe/Krick Najade Brushless set up question
« on: May 09, 2021, 07:01:13 pm »

Hi all,
I've just ordered myself a RoMarin Najade having just eventually finished my AeroNaut Jenny. I'm wandering which is the best set up for the Najade. I'm thinking along the lines of a 36mm brushless inrunner (not sure what is the best kV to have), watercooling, running on lipo (not sure of the difference between parallel and in series!....bit thick on sparky bits!). I dont want the boat to turn the water to steam when its got its bottom wet but I dont want it to be a slouch either. I've seen some brushless motors online but the either seem to be always from China and the scary import taxes etc, out of stock, out of production, crap reviews or inexplicably expensive. Really need some help on this to get the best set up for the boat without breaking the bank!
Also any advice on building the Najade would also be very well received.


All the breast,
Dave
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malcolmfrary

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Re: RoMarin/Robbe/Krick Najade Brushless set up question
« Reply #1 on: May 10, 2021, 09:42:57 am »

running on lipo (not sure of the difference between parallel and in series!....bit thick on sparky bits!).
Series, all of the cells are in a row like a string of sausages and you get more volts.  For the same motor, this means a much faster spinning motor, but with proportionately less run time.
Parallel, all of the positives are connected together, all of the negatives are connected together.  Same voltage, but lots more AH so it runs longer.  Again, same motor considered. 
Different motors, that is motors intended for the voltage that you are going to give them, different considerations apply.
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kinmel

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Re: RoMarin/Robbe/Krick Najade Brushless set up question
« Reply #2 on: May 10, 2021, 11:55:23 am »

Model Shop Leeds recommends a 3652-06 brushless motor.
I personally prefer a Turnigy Aero outrunner motor around 1000Kv, available from Hobbyking's UK warehouse.  An outrunner will run cooler than an inrunner and you will probably not need water cooling.
I suggest 3S Lipos as a starting point.
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davejay

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Re: RoMarin/Robbe/Krick Najade Brushless set up question
« Reply #3 on: May 10, 2021, 12:10:27 pm »

Model Shop Leeds recommends a 3652-06 brushless motor.
I personally prefer a Turnigy Aero outrunner motor around 1000Kv, available from Hobbyking's UK warehouse.  An outrunner will run cooler than an inrunner and you will probably not need water cooling.
I suggest 3S Lipos as a starting point.


Thanks Kinnel. The only problem is that I think that the motor mounting within the Najade is favoured towards a brushed motor version and hasn't been updated to allow for mounting a outrunner but more for mounting an inrunner, not 100% sure of the set up as I haven't yet got my sticky mitts on it yet.
Ironically it's Model shop Leeds where my Najade is coming from!

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davejay

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Re: RoMarin/Robbe/Krick Najade Brushless set up question
« Reply #4 on: May 10, 2021, 12:15:28 pm »

Series, all of the cells are in a row like a string of sausages and you get more volts.  For the same motor, this means a much faster spinning motor, but with proportionately less run time.
Parallel, all of the positives are connected together, all of the negatives are connected together.  Same voltage, but lots more AH so it runs longer.  Again, same motor considered. 
Different motors, that is motors intended for the voltage that you are going to give them, different considerations apply.


Thanks Malcolm for making that a whole lot clearer. Mentioning strings of sausages made me hungry!
So, if I was to have two six cell 11.1v 5000mAh batteries connected via a 'Y' harness would give me 22.2v but still 5000mAh or would that give me 11.1v still but 10,000mah? I understand the fact that volts give you the power/oomph and mAh give the duration!


Regards,
Dave
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davejay

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Re: RoMarin/Robbe/Krick Najade Brushless set up question
« Reply #5 on: May 10, 2021, 12:36:56 pm »

I've been looking at the Hobbywing SeaKing set up consisting of a Hobbywing Seaking 3660SL inrunner 3180kv and a Hobbywing SeaKIng 120a speed controller.....both watercooled. An expensive set up at around 150 but I would like the best for the Najade as I intend to make it as the best boat I've built.....a stand out model which has the wow factor for not only myself but for anyone that sees it. I just don't want it to be overpowered as I have heard that the Najade suffers a tad from digging in on tight turns..........I don't want an offshore racer but a good scale performer (scale speed is a big thing for me.....I hate seeing scale warships etc doing a scale 70knots......same with model railways, an 8F steamer doing 150mph scale speed!)
Its the 3180kv that worries me......thats 3180rpm per volt right, so on a 11.1v lipo that motor will spin at about 34,000rpm at full throttle which seems a crazy amount, I know there will be a reduction when the prop is in the water but its still going to be about 30,000rpm at full throttle. OK I could back of the throttle a tad and run at 3/4 throttle but dont brushless motors work more efficiently at full bore?
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malcolmfrary

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Re: RoMarin/Robbe/Krick Najade Brushless set up question
« Reply #6 on: May 10, 2021, 04:23:37 pm »


Thanks Malcolm for making that a whole lot clearer. Mentioning strings of sausages made me hungry!
So, if I was to have two six cell 11.1v 5000mAh batteries connected via a 'Y' harness would give me 22.2v but still 5000mAh or would that give me 11.1v still but 10,000mah? I understand the fact that volts give you the power/oomph and mAh give the duration!


Regards,
Dave
Depends on the type of harness, you can get both series and parallel.
If it is a series Y harness, 22.2 volts with 5000mAH.  The voltages add up.
If a parallel harness, 11.1 volts with 10000mAH.  The mAH capacity adds up.
And, of course, 11.1 volts is the result of 3 cells in series.  2 packs in series, 22.2 volts.  2 packs in parallel, twice the mAH stored thus longer run time.
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