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>> Home > Forum > Electrical Related > Brushless motors (again)
Brushless motors (again)
(464 views)
Author Message
steve-d
(Lieutenant)





Forum Posts: 35
28th Oct 2018 18:00  
>> Permalink
mdlbt.com/47525

Again, as not wanting to nick someone else's thread.

Huntsman 31 currently has a geared (belt) brushed motor which was probably quite a good spec. many years ago. I don't remember how quick it was but having watched brushless boats running this morning in Southsea I have decided now is the time for change before I start painting.

I've been reading various threads and gleaned some info but it is still a minefield. Whilst this boat (original) is twin screw I am not yet ready to go that far so will stay single screw.

A thread suggested 3639 -1100KV which is fine as a spec. but there are a zillion different makes and models for that spec.
Cornwall models seem to offer 6 or 8 so I am looking for more specific advise for make and model of each piece of the power system...motor, ESC, battery, charger.

I'm not going to say 'money no object' just that I don't 'need' to buy bottom spec.

I suspect there will be as many different suggestions as 'Cornwall' have motor makes but something good will come out of it.
Many thanks
Steve


Attached Files - Click To View Large

canabus
(Fleet Admiral!)





Forum Posts: 126
29th Oct 2018 05:22  
>> Permalink
mdlbt.com/47539

Hi Steve
I started with the Hobbyking 3639-1100 kv in my Huntsman with a 2 blade 40mm prop, 3S 5800mah Lipo and a car 60 Amp ESC.
Upgraded to the 100Amp car ESC and a straight change over to the 3648-1450 motor.
All from Hobbyking.
Good units and have no problems.
Also a the price will not break the bank book!!!
Note, change the uni-joint to metal as the plastic ones will not handle the power and break.
Canabus

steve-d
(Lieutenant)





Forum Posts: 35
29th Oct 2018 12:12  
>> Permalink
mdlbt.com/47545

Any specific reason you refer to a 'car' ESC?
What size (dia.) shaft should I use?
Will I need to cool that motor?

Cheers
Steve

Haverlock
(Fleet Admiral!)





Forum Posts: 499
29th Oct 2018 16:57  
>> Permalink
mdlbt.com/47551

depending upon the type of motor cooling it can be a problem. Most brushless motors are out runners so the case rotates! In runners are usually for higher speed applications (or driving a gearbox). If you have an idea as to the size of IC engine the boat was intended to have then this list may be a help


.049 or .051 = 100 watts

0.10 = 200 watts

0.15 = 300 watts

0.25 = 500 watts

0.32 = 640 watts

0.40 = 800 watts

0.45 = 900 watts

0.51 = 1020 watts

0.61 = 1220 watts

0.75 = 1500 watts

0.91 = 1820 watts


Since Watts are Volts * Amps ( I know this is not accurate for a reactive load like an electric motor but its a rule of thumb)

This gives you a ball park next point is the KV ( revs per volt) of a motor. The higher the KV the smaller the prop. Finally buy a Watt meter they are not expensive and give you a chance to " fine tune" a setup.

https://www.ebay.co.uk/itm/FT08-RC-150A-Hight-Precision-Watt...

Car ESCs ( usually) have a reverse function while the airplane versions do not. They are generally cheaper than boat specific ESCs.


"that's not a bug its just an undocumented creature."

Sir Terence David John "Terry" Pratchett, OBE (28 April 1948 - 12 March 2015)
steve-d
(Lieutenant)





Forum Posts: 35
29th Oct 2018 23:06  
>> Permalink
mdlbt.com/47562

Boat was designed for 5cc = .32 = 640W = 58A

Bought the watt meter.

Both the motors mentioned above are back order.

onetenor
(Fleet Admiral!)





Forum Posts: 451
30th Oct 2018 05:21  
>> Permalink
mdlbt.com/47565

Seen this====https://www.designnews.com/automation-motion-control/small-c...

Haverlock
(Fleet Admiral!)





Forum Posts: 499
30th Oct 2018 05:26  
>> Permalink
mdlbt.com/47566

This looks like a BEAST https://www.rapidrcmodels.com/ntm--4248-650kv-v2-brushless-o... run it on a 4s battery ( ok go 5s and a smaller prop)


"that's not a bug its just an undocumented creature."

Sir Terence David John "Terry" Pratchett, OBE (28 April 1948 - 12 March 2015)
onetenor
(Fleet Admiral!)





Forum Posts: 451
31st Oct 2018 21:52  
>> Permalink
mdlbt.com/47625

Certainly see👍ms a good spec.

steve-d
(Lieutenant)





Forum Posts: 35
1st Nov 2018 12:20  
>> Permalink
mdlbt.com/47634

Will need to put this on hold for a bit as I have just discovered a guy working in the next industrial unit to mine is into boating and has offered to give me a motor and ESC that he has 'outgrown'.

In the mean time I need to replace the propshaft as it is not man enough plus a metal U/J. Bit of hacking required.