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Author Topic: brushless help  (Read 7749 times)

bill stafford

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brushless help
« on: May 30, 2015, 01:11:49 PM »

dear gents,
I need some help, for a change.
I read on this site were some people were using brushless to drive 60mm props, via 6V battery, a hobby king SK-3 motor, but little mention of there speed control
I am about to try brushless for drive motors ,and the other mayhem members seemed to know all about these motors in tugs,so I wish to ask about speed controls
what do you use, are the hobby king ones any good for scale tugs?? are the hawke any better.
I have a rc car/buggy version to play with, but it tends to be "lumpy", and not briliant ,for scale tugs.I intended to use brushless w 3:1 gear boxes, home made , to make them "throttle" better
thanks for any help
bills
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Calimero

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Re: brushless help
« Reply #1 on: May 31, 2015, 01:46:03 PM »

Go direct drive, please. No need to use the dreaded gearbox with BLDC motors.

What prop exactly are you going to use ? What manufacturer (Prop Shop, Raboesch ...) ? What type and what pitch ?

I'd go with a 500kv motor under 6V. If your tug has 60mm props, I assume you could fit a couple of nice big 6V SLA batteries.

Here's a big nice SK3 motor at HK : Turnigy Aerodrive SK3 - 5045-500kv Brushless Outrunner Motor

There's also a 450kv version of the same. Might be even more suitable.

ESC-wise we've used these with great success once programmed with the right settings:
HobbyKing® ™ Brushless Car ESC 45A w/ Reverse
HobbyKing® ™ Brushless Car ESC 60A w/ Reverse

There's also the Trackstar 1/10th 60A car ESC which works great but is currently out of stock.

Smooth throttle response. Very low rpm start. Standard forward/reverse with no brake.
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Calimero

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Re: brushless help
« Reply #2 on: May 31, 2015, 01:47:28 PM »

Oops didn't notice your were down under and put links to the UK warehouse. But you should be able to find all that stuff either from the Aussie warehouse or their international/HK warehouses.
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mermod

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Re: brushless help
« Reply #3 on: May 31, 2015, 01:58:19 PM »

I use the Hawk speedies and love em, do get the programmer though.


Phill
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Re: brushless help
« Reply #4 on: May 31, 2015, 02:03:24 PM »

If you get a chance have a look at my stan tug build, i used hobbyking sk3 motors and hawk esc's, plenty of low end control but i do run them on 12volt. http://www.modelboatmayhem.co.uk/forum/index.php/topic,42633.200.html
I know the importers of Hawk in Aus and they have excellent backup as far as warranty, if you have trouble getting Hawk then the new range of OS esc's are exactly the same and use the same hawk programmer, might be worth a look here....http://www.worldhobbies.com/home_rc_radio_control_models_os_engines_castle_page.html.

Phill
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bill stafford

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Re: brushless help
« Reply #5 on: June 01, 2015, 02:04:58 PM »

gday gents ,
     thank you so VERY much , this info was exactly what I was asking for, its hard to beat experience!!!
I will get some of these motors+probably the Hawk s/c soon.
I have my own drawing for the ocker white tug, approx. 750/800mm loa, 1/32 scale , that I have drawn up ,simplified ,aimed at beginners, that will make a nice test bed,as its not a copy of the other tug,I called it " ocker white".
Phil  I love you tug, so much detail!! I have also built your white tug in the back ground, mine has 55 mm 4 blade prop+decerperm for power,but I'm not over happy w its power, I feel it needs 2 props, what drives it
regards bill


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bill stafford

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Re: brushless help
« Reply #6 on: June 01, 2015, 11:42:22 PM »

ps page , sorry gents , i mucked up the repley,
tug name is knocker white , as the original tug ,my version , i have tear  dropped the hull form, simplified hull shape and drive area,but I had low detail on the engine casing area+stern,so I took a bit of a guess?? it is aimed at a intermediate beginner , looks like a tug ,so must be a tug LOL most details /hard ware home made
I was originally intended to go w 545 drive , via tooth belts of 3:1 ratio , to nozzle w 60mm brass prop, plenty of grunt!!
i also use brass props on my models , Raboesch breed , more pitch and bite than plastic props
on my current G Guest paddle tug, im building a becker rudder, to help turn the beast
regards bill s
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Calimero

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Re: brushless help
« Reply #7 on: June 02, 2015, 12:42:05 PM »

The Raboesch #174 prop gives great pull. I'll use two of them, 55m dia, in Kort nozzles in my next twin screw springer.
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mrlownotes

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Re: brushless help
« Reply #8 on: June 02, 2015, 08:56:36 PM »

Don't the SK3 aero motors need any sort of cooling, being contained in the hull ? I'm assuming that in their 'airborn' function they would be in a very good airflow.
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Bintur Ellenbach

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Re: brushless help
« Reply #9 on: June 02, 2015, 09:09:14 PM »

If you run them at 6V and props < 70 mm definetly no  {-)
At 12V with 100 mm Prop yes
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regards

Tobias

mrlownotes

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Re: brushless help
« Reply #10 on: June 02, 2015, 09:16:55 PM »

If you run them at 6V and props < 70 mm definetly no  {-)
At 12V with 100 mm Prop yes

Hmmm, I thinkI should forget about running them on a 5S Lipo (18.5V) with a 50mm 3blade propshop prop. It may get  a bit warm in there.
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Bintur Ellenbach

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Re: brushless help
« Reply #11 on: June 02, 2015, 09:53:33 PM »

Well, a 40" tug boat can reach a speed of 2.8 mph. It won´t get faster!!! no matter what you do (extreme overpowering to bring it to planing excluded :} )

On a "usual" 50 mm brass prop with pitch ratio of around 1 you´ll need exactly 2150 rpm to reach that speed.
You will want to add around 20-30% to that to create a giant bow wave on the hull --> 2800 rpm.
Any higher rpm will just increase the current (and slightly the waves created by the hull) but do NOTHING ELSE.

On 5S the motor would need 150kv or with the given kv of 500 you should run the SK3 motor on around 6,2V to reach the 2800 rpm (free wheeling rpm * 0,9 to get rpm under load).

With the 40" tug at estimated 40-50 pounds weight  I estimate the current draw:
at 6V around 10-15 Amps --> around 60W outgoing power on the prop
at 5S at least 30-50 Amps --> at least 600W drawn out of the battery  {-)
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regards

Tobias

mrlownotes

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Re: brushless help
« Reply #12 on: June 02, 2015, 10:16:57 PM »

Thankyou Time Bandit. I've got my head around it now.
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Bintur Ellenbach

Calimero

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Re: brushless help
« Reply #13 on: June 02, 2015, 10:51:03 PM »

Any higher rpm will just increase the current (and slightly the waves created by the hull) but do NOTHING ELSE.

Well you'll probably get more bollard pull which is nice on a tug.


Quote from: Time Bandit

With the 40" tug at estimated 40-50 pounds weight  I estimate the current draw:
at 6V around 10-15 Amps --> around 60W outgoing power on the prop
at 5S at least 30-50 Amps --> at least 600W drawn out of the battery  {-)


Probably more than that. Propeller type is as much a factor as is the diameter, I suspect.


A 45mm #174 prop on a SK3 3542-800kv under 6V draw around 10.5A (66W).


Under 11.1V (3S) current is around 29A and we're way past the max rpm suggested by Raboesch.
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Time Bandit

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Re: brushless help
« Reply #14 on: June 03, 2015, 02:33:03 PM »

Well you'll probably get more bollard pull which is nice on a tug.



Probably more than that. Propeller type is as much a factor as is the diameter, I suspect.


A 45mm #174 prop on a SK3 3542-800kv under 6V draw around 10.5A (66W).


Under 11.1V (3S) current is around 29A and we're way past the max rpm suggested by Raboesch.

Bollard pull is not affected too much by rpm, the prop starts to cavitate pretty soon during bollard pull tests, normally way below the rpm for "hull speed" is reached. Main factor here is the prop itself (blade area...)
You´ll see that if you measure the bollard pull at different rpm, it has a maximum somewhere and the get´s lower again if you increase rpm.

A "usual" displacing hull needs between 2W and 3W per kg of the boat´s weight (output power not input) to reach hull speed and a "nice" bow wave, IF the rpm and prop pitch (diameter is not such a big factor) match the possible hull speed of the boat.
That´s why I came up with the 10-15A.
If the rpm is too high the current increases to create "waves".

Not sure about the "5S current", could be way more, but I intend to believe that the prop will not have enough grip to produce currents over 50A.

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regards

Tobias

Calimero

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Re: brushless help
« Reply #15 on: June 03, 2015, 03:03:54 PM »

Well, under 5S it would probably be useless.


I'll try and check BP at various engine speeds. I have only measured it at full throttle (which is below max recommended RPM) so far
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bill stafford

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Re: brushless help
« Reply #16 on: June 04, 2015, 02:29:33 PM »

hello gents,
 what uni`s do you use on brushless,I notice the damen tug has a different version , to what im used too seeing.
 if I use a 12V battery+50/65mm prop , do I have to water cool motor ?? and what about speed control , I read some s/c units need cooling
in the motor section of the SK-3, there is a water cooled mount, radiator+water pump, any good??
thanks for all your help,
        regards bill s
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Calimero

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Re: brushless help
« Reply #17 on: June 04, 2015, 02:59:29 PM »

It goes the other way around.

What tug are you building ?  What scale ? --> what is the original props' diameter ? --> get the right props from Prop Shop or Raboesch --> choose the right motor/battery

You won't need water cooling on a tug.
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bill stafford

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Re: brushless help
« Reply #18 on: June 05, 2015, 08:42:59 AM »

gday calimero,
 thanks for your help, I havent decided on the next project yet,but I want to try brushless.
I have self drawing for the knocker white tug ,approx 750mm loa, 50/60mm prop in a nozzle, in 1/32 ,and this will probably be the test bed for the brushless drive, props.[size=78%] raboesch[/size]
i do most of my models in 1/32, typically 50/65mm props, some twin ,some single,so I`m trying to get some ideas for a future model , using brushless for power , in the past 545w 3:1 tooth belt gear-boxes
hope this makes sense
regards bill S
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TugCowboy

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Re: brushless help
« Reply #19 on: June 05, 2015, 09:31:03 AM »

Depending on the weight of that model, Bill, you should be absolutely fine with an SK3. But possibly think about 6v rather than 12. Those brushless motors have a lot of torque and will give a very scale performance at 6v unless the boat is very heavy.

Alex
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Calimero

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Re: brushless help
« Reply #20 on: June 05, 2015, 09:59:27 AM »

thanks for your help, I havent decided on the next project yet,but I want to try brushless.
I have self drawing for the knocker white tug ,approx 750mm loa, 50/60mm prop in a nozzle, in 1/32 ,and this will probably be the test bed for the brushless drive, props.[size=78%] raboesch[/size]


For a 60mm prop, I'd go with a 400-500kv outrunner under 6V
For a 50mm prop, you could go a little faster. There's a 620kv 42mm outrunner in the SK3 range.


I was actually going to use two of those 620kv 42mm outrunners with 6v SLA batteries in my twin screw springer tug (with 55m #174 Raboesch props). I even already have the motors (nicely built, as are usually the SK3) but I've changed my mind and will switch from SLA batteries to 9.9V LiFePo4. Those 620kv motors are then of course too fast.


Thanks to the drone guys HobbyKing now has small and slow brushless outrunners. I got a 360kv 35mm motor in the mail to test it. So light I'll be able to completely forego any motor mount. I'll replace the motor shaft with ... the propeller shaft and be done with it. No alignment problems !
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tsenecal

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Re: brushless help
« Reply #21 on: June 05, 2015, 05:50:15 PM »


With the 40" tug at estimated 40-50 pounds weight  I estimate the current draw:
at 6V around 10-15 Amps --> around 60W outgoing power on the prop
at 5S at least 30-50 Amps --> at least 600W drawn out of the battery  {-)


with approximately 540W of the 5S setup being sent out of the system as heat.
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bill stafford

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Re: brushless help
« Reply #22 on: June 06, 2015, 02:55:59 AM »

gday gents,
 tug weight ,im guessing a bit , but,4.5/6 kg approx. ??
it is only 750mm loa,draws about 65mm of water , typical thames river tug ,w limited/non sea going duties, its a bit hard to be more accurate[size=78%],as its not built yet[/size]
all of my other models are 12 v battery , so plenty of 12 V chargers , not so in the 6 V area, so I would prefer to use 1 battery , of the 12 version ,but I am flexible
thanks for all the help , I have read EVER word , and am taking it all in
bill S
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Time Bandit

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Re: brushless help
« Reply #23 on: June 06, 2015, 09:54:00 AM »

if you want to stick to 12V you should get a 300kv Outrunner.

Like the Robbe Roxxy C35-30-45 with 300kv. Has enough power for a 10 kg boat.
The SK3 seems to big for such a boat anyways.


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regards

Tobias

bill stafford

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Re: brushless help
« Reply #24 on: June 06, 2015, 01:19:47 PM »

gday tobias,
 i dont trhink I can get robbe motors out her , in australia, but hobby king is available
most brushless are to high in Kv revs,aimed at model planes ??, but i will look around.
I think there were some low kv at hobby king,but for helo`s. but B IG bucks !!I am price shy,at this stage ,as I havent got brushless to compare too,what I do have are for planes.
alimero, were are those quode motors at hobby king?? and what part no.??
most have large shafts through motor,and 4/5mm prop shafts couldnt be mounted easily to them
I am ordering 2+SK-3 w500Kv ratings, I will play w them ,soon to get hawk 50A s/c +card
that will give me a starting point, either 6 or 12V SLA batteries , but if I can avoid saddle pack batteries, I will
regards and thanks heaps bill s
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