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Author Topic: Brushless motor for Model Slipway Maggie M  (Read 488 times)

clockworks

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Brushless motor for Model Slipway Maggie M
« on: August 11, 2019, 02:35:57 PM »

Kit should be arriving in a couple of days, so I'm thinking about the parts needed for the build.


Finished model is 850mm long, displacement about 10 kilos. It comes with a 50mm brass prop and an M4 shaft. It's a fishing boat, so not looking for crazy speeds.


The motor recommended by Model Slipway is a 540 with a 2.5:1 gearbox on 6 volts, but I want to use a brushless setup. I already have a couple of 5000mAH 2s LiPos, so I will use those in parallel.


I'll be buying the motor and ESC from Hobbyking. Obviously I need a motor with a fairly low kv, but what size?
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ANDY
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Taranis

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Re: Brushless motor for Model Slipway Maggie M
« Reply #2 on: August 11, 2019, 04:00:21 PM »

I should have said I could not find anything suitable at hobbyking
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ANDY
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clockworks

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Re: Brushless motor for Model Slipway Maggie M
« Reply #3 on: August 11, 2019, 04:20:54 PM »

Thanks for the links. I can't find anything suitable at Hobbyking either. All their slower-revving motors are for 4s minimum. I could wire my two 2s packs in series to satisfy the voltage requirement, but then it would rev twice as fast.


The website you linked to doesn't give much info on the motor specs. Are they OK on 2s, and what's the max current?

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Taranis

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Re: Brushless motor for Model Slipway Maggie M
« Reply #4 on: August 11, 2019, 04:34:29 PM »

For 2s I would look at the 400kv


I collect mine tomorrow from post office so may be able to offer more info
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ANDY
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coch y bonddu

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Re: Brushless motor for Model Slipway Maggie M
« Reply #5 on: August 11, 2019, 04:36:15 PM »

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clockworks

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Re: Brushless motor for Model Slipway Maggie M
« Reply #6 on: August 11, 2019, 04:42:43 PM »

That Component Shop motor looks ideal - thanks
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Taranis

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Re: Brushless motor for Model Slipway Maggie M
« Reply #7 on: August 11, 2019, 04:53:10 PM »

Look very good  :-))
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ANDY
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DaveM

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Re: Brushless motor for Model Slipway Maggie M
« Reply #8 on: August 11, 2019, 05:46:23 PM »

I can certainly testify to the performance of that 30A speed controller - I have three.
DaveM
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unbuiltnautilus

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Re: Brushless motor for Model Slipway Maggie M
« Reply #9 on: August 11, 2019, 07:26:43 PM »

Thanks for the links. I can't find anything suitable at Hobbyking either. All their slower-revving motors are for 4s minimum. I could wire my two 2s packs in series to satisfy the voltage requirement, but then it would rev twice as fast.


The website you linked to doesn't give much info on the motor specs. Are they OK on 2s, and what's the max current?


I wouldn't worry too much about the recommended voltage. That voltage is intended to pull an aircraft off the ground turning a big aircraft prop, not drive a scale boat. Brushless motors obviously start up at a low voltage, you then rev up to full speed. I have used not many but some brushless, and am planning more, for scale and fast scale models. I am usually looking below the normal suggested voltage range to get the performance I need at the prop.
Saying that, it's Component Shop over Hobbyking every day of the week and three times on Sunday!
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Re: Brushless motor for Model Slipway Maggie M
« Reply #11 on: August 12, 2019, 09:16:53 AM »


I wouldn't worry too much about the recommended voltage. That voltage is intended to pull an aircraft off the ground turning a big aircraft prop, not drive a scale boat. Brushless motors obviously start up at a low voltage, you then rev up to full speed. I have used not many but some brushless, and am planning more, for scale and fast scale models. I am usually looking below the normal suggested voltage range to get the performance I need at the prop.
Saying that, it's Component Shop over Hobbyking every day of the week and three times on Sunday!



I thought that ESCs worked by switching the full battery voltage, rather than by reducing the voltage? Pretty sure that brushed ESCs vary the pulse width, and brushless ESCs vary the switching frequency between phases, but always apply full battery voltage while "on".


If the voltage applied to a brushless motor is too low, it won't turn at all - not enough "pull" from the energised coil to overcome the magnets. They will quite possibly work at a lower voltage than the recommended range, but will a motor specced for 4s to 6s work on 2s?
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malcolmfrary

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Re: Brushless motor for Model Slipway Maggie M
« Reply #12 on: August 12, 2019, 09:46:57 AM »

Good question.
With brushed motors, the ESC and motor can be checked out separately, but not so with brushless, where the ESC and motor are effectively part of the same package.
Or does the motor technically work when presented with a lower voltage in that it rotates but actually operates in a semi-stall mode at much reduced efficiency?
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Taranis

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Re: Brushless motor for Model Slipway Maggie M
« Reply #13 on: August 12, 2019, 10:48:52 AM »

To my understanding the motor and ESC will work within the range of the voltage presented to them.
The voltage does not vary the speed but it will dictate the maximum possible speed.
The speed is controlled by the ESC adjusting the timing of the phase changes rather than varying the voltage

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Re: Brushless motor for Model Slipway Maggie M
« Reply #14 on: August 12, 2019, 01:20:10 PM »

This is why we test things, too much theory, not enough practice!
I did a performance chart when setting up my Precedent Perkasa, over on the Warships bit, (Perkasa to Brave Swordsman). I started at 4.8v both in and out of the water. The Leopard motor was listed as a 2 to 4S designed, while the Ripmax Quantum II 20 was listed as a 4S. So starting at just above 1S, both motors were happy to fire up and rotate both in and out of the water, with torque.
So, I don't know if my description was materially accurate, but I stand by the 'in the water' tests disproving this voltage thing. I still stand by my thoughts that the recommended voltages of most of these motors are aimed at getting an aircraft off the ground with the recommended prop. Even the Component Shop listing is recommending suitable aircraft prop sizes, even on the low Kv one listed a few posts back. A very large prop I might add, lots of useful boaty torque!
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Re: Brushless motor for Model Slipway Maggie M
« Reply #15 on: August 12, 2019, 02:15:49 PM »


If the voltage applied to a brushless motor is too low, it won't turn at all - not enough "pull" from the energised coil to overcome the magnets. They will quite possibly work at a lower voltage than the recommended range, but will a motor specced for 4s to 6s work on 2s?
In my ST Cruiser I used a low Kv aircraft motor intended for 6s on a 3s pack, more than enough power. In fact I had to reduce the esc output to keep the speed down. In the plane around 40/50A, in the boat around 4/5A. I don't have a high capacity 2S pack or would have tried that.
Jim
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clockworks

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Re: Brushless motor for Model Slipway Maggie M
« Reply #16 on: August 13, 2019, 08:51:26 AM »

I've ordered the motor and ESC from Component Shop.
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