Model Boat Mayhem
Technical, Techniques, Hints, and Tips => BRUSHLESS Motors and Speed Controllers => Topic started by: Lt. Raen on December 05, 2009, 12:24:58 am
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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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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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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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: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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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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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 (http://eetweb.com/motors-drives/efficiency-coreless-servomotors-20091001/) 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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The problem at the moment with brushless motors is the difficulty in obtaining one which will reverse the motor
Huh? {:-{
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Huh? {:-{
Why not just list a selection for him?
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No problem, a selection of what?
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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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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 (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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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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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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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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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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It's in English hobbyspeak.
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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