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Author Topic: Brushless motors??  (Read 3383 times)

Lt. Raen

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Brushless motors??
« on: December 05, 2009, 12:24:58 AM »

G'day

  New to the forum here so sorry if i ask lame questions. Anyway i have decided to scratch build a model speed boat and am looking at a method to power it. After looking at some rather confusing info floating around i think i have settled on going brushless for their increased efficiency (and therefor runtime????)
  I am looking at the Team losi 1/18 scale motors (http://www.losi.com/Search/Default.aspx?SearchTerm=1/18%20brushless) or dynamite c4 (http://www.dynamiterc.com/Products/Default.aspx?ProdID=DYN3715) from http://www.rchobbies.com.au/store/index.php?cPath=339_29&page=1&sort=4a&osCsid=9ca3e845610bd5afc6ef5a17ed1f4550 but cant work out which Kv to go for.
Any recomendations??
Plus what esc would i need for these i was thinking of going with the team losi one but i think these were built for cars.

Cheers Tim
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Ivor Bittle

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Re: Brushless motors??
« Reply #1 on: December 05, 2009, 03:34:03 PM »

Do you have any genuine figures for the actual increase in efficiency of a brushless motor over a brush motor? If you have, share them with us. I thought that brush motors were up in the high eighty percents so there is not much room for large increases.

Ivor Bittle
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stallspeed

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Re: Brushless motors??
« Reply #2 on: December 05, 2009, 05:37:50 PM »

Tim,if you want really efficient motors then,by all means, go for brushless coreless motors but the operative word is coreless,not brushless.
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Lt. Raen

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Re: Brushless motors??
« Reply #3 on: December 06, 2009, 07:18:42 AM »

 :o Ahhh right i thought that all brushless motors were the same
seems i have fallen into the old "assuming" trap  :((
My understanding was that as brushless motors used electromagnets with Alternating Current (provided by the ESC) to create the core to spin, this would provide large benefits (i would have thought) when compared with normal brushed DC motors due to a decrease in frictional forces present. Of course i have likely gotten this hole affair warped in my mind :D
In this case what size DC motor should i go for and would a DC motor not make an ESC irrelevant as a potentiometer connected to a servo would be able to serve as a rather simple (and crude) ESC with the only drawback being size and a lack of reverse (and reverse doesn't seem to be a feature of all ESC's anyway"

Thanks from a rather confused Aussie, Tim :)
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FullLeatherJacket

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Re: Brushless motors??
« Reply #4 on: December 06, 2009, 08:44:24 AM »

Tim
This should answer a few questions about how ESCs for what you call 'DC motors' work.
http://www.action-electronics.co.uk/pdfs/ESCs.pdf
The problem at the moment with brushless motors is the difficulty in obtaining one which will reverse the motor - not terribly important for out-and-out speed but essential when fitting one into a workboat model (e.g. tug). If you can live with that limitation for the time being then there are a lot of brushless motors and speed controllers out there.
I'm sure Mr Speed means well but don't beat yourself up trying to find a coreless and  brushless motor; go with the herd! There's plenty of relevant stuff on this forum.
FLJ
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stallspeed

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Re: Brushless motors??
« Reply #5 on: December 06, 2009, 12:41:48 PM »

Tim,what you assume about better efficiency of brushless due to the elimination of the brushes is true to an extent but the benefits in brushless motors are seen in aircraft and fast boats where the brushless motors are more tolerant of a hammering.
For endurance,though,peak motor efficiency occurs when the iron losses equal the copper losses so if you have low iron losses you have a high efficiency peak.
This is a recent article
on such motors but it points out where the efficiency gain comes from.
Brushed coreless motors can be obtained but ones suitable for a speedboat cruiser? {:-{
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andygh

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Re: Brushless motors??
« Reply #6 on: December 06, 2009, 01:47:42 PM »

Quote
The problem at the moment with brushless motors is the difficulty in obtaining one which will reverse the motor


Huh?  {:-{
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stallspeed

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Re: Brushless motors??
« Reply #7 on: December 06, 2009, 01:59:39 PM »

Huh?  {:-{
Why not just list a selection for him?
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andygh

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Re: Brushless motors??
« Reply #8 on: December 06, 2009, 03:11:14 PM »

No problem, a selection of what?
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stallspeed

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Re: Brushless motors??
« Reply #9 on: December 06, 2009, 03:33:58 PM »

FLJ was talking about escs so that was the context.
It was a valid point too.Within a reasonable budget,there isn't the same broad choice as reversing brushed escs.
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andygh

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Re: Brushless motors??
« Reply #10 on: December 06, 2009, 04:09:15 PM »

I sort of agree, you do have to shop around a bit.
There are a few here http://www.giantcod.co.uk/boat-escs-c-21_166.html and the odd one elsewhere in the UK.  If you're prepared to deal with companies in the Far East there are plenty of choices and cheap too, for now.
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red181

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Re: Brushless motors??
« Reply #11 on: December 07, 2009, 11:39:38 PM »

castle creations in USA do reversing esc's for brushless applications, offshore electrics are a supplier, and have their own forum, which you might find useful, also rcgroups.com have a section dedicated to castle creations, very good, but, very expensive :-))
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Lt. Raen

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Re: Brushless motors??
« Reply #12 on: December 08, 2009, 07:42:06 AM »

well i can live without reverse for now but how can i compare the performance of a brushless motor to a brushed motor using just the listed specifications?
Also with the ESC's would one of these be suitable (http://www.rchobbies.com.au/store/product_info.php?cPath=341_30&products_id=4588&osCsid=484e948543c099795cc0216a56e22fe4) or am i better off with something like this (http://www.rchobbies.com.au/store/product_info.php?cPath=341_30&products_id=2314&osCsid=484e948543c099795cc0216a56e22fe4) plus how can i work out what motors these aer rated to?????

man this is a lot more confusing than i thought it was going to be :D

I also forgot to mention that at this stage the model will most likely be 350 mm long approximately

Thanks again for all the advice

Tim
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stallspeed

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Re: Brushless motors??
« Reply #13 on: December 08, 2009, 01:33:26 PM »

Quote
BEC / Electric power supply of the receiver   5.0V
Set-up Procedure   yes
Fail Safe System   yes
Weight   19.0g
Size   26.0 x 26.0 x 15.7mm
High frequency   yes
Motorlimit   over 18 Turns
Multi-Protection-System   yes
Voltage Input   4.8-7.2V
Connectors   Standard Tamiya Stlye
Rated Current   60 A
Typical Voltage Drop @20A   0.144V
forward/brake/reverse   yes
Waterproof   yes
I've never used it but I can spot an esc with a misleading current rating when compared against data.Here,I mean the 60 amp with the Vdrop of 0.144.I can't see the cooling for the power loss generated.
I have done an 18" and a 24" speedboat with a standard brushed AUD$10 540 & 7.2 pack supplying more than enough power for both.
Is it really duration you want or speed?
Either way,you can scratch a zero off your budget and it is probably a wise thing if it is the first boat.The boat is so small I think it is actually worthwhile starting with el cheapo 400 size brushless.

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HS93 (RIP)

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Re: Brushless motors??
« Reply #14 on: December 08, 2009, 01:35:55 PM »

I've never used it but I can spot an esc with a misleading current rating when compared against data.Here,I mean the 60 amp with the Vdrop of 0.144.I can't see the cooling for the power loss generated.
I have done an 18" and a 24" speedboat with a standard brushed AUD$10 540 & 7.2 pack supplying more than enough power for both.
Is it really duration you want or speed?
Either way,you can scratch a zero off your budget and it is probably a wise thing if it is the first boat.The boat is so small I think it is actually worthwhile starting with el cheapo 400 size brushless.



Can we have it in English please  >:-o

peter
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stallspeed

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Re: Brushless motors??
« Reply #15 on: December 08, 2009, 01:39:44 PM »

It's in English hobbyspeak.
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Lt. Raen

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Re: Brushless motors??
« Reply #16 on: December 09, 2009, 08:10:08 AM »

Speed is definitely the higer priority but i dont want a boat that lasts 5min and then i have to wait an hour to recharge
hmmm i think i might go a cheap motor and work from there thanks for the advice guys :)
now i just need to get building lol
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