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Author Topic: what brushless motor would replace a brushed 700 motor  (Read 14249 times)

Dekan

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what brushless motor would replace a brushed 700 motor
« on: August 04, 2010, 10:18:52 PM »

I am thinking of building a traditional style british cabin cruiser

What I wanted to know is how big a brushless motor you would need to replace the suggested speed 700 and whether there was some formula or rule of thumb in comparing brushed and brushless motors when used in a boat
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Prophet

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Re: what brushless motor would replace a brushed 700 motor
« Reply #1 on: August 04, 2010, 10:39:40 PM »

bigger motors faster they go :) I'm currently building a huntsman cabin cruiser that will run twin props i will be working up to twin Graupner 800's but will start with my current spares 2 540's.
difference betwee brushed and brushless motors is that brushed motors offer better performance but at a price to regular brush replacements at cost 5 a set for good quality.

Brushless well thats answers itself good all round motors less maintenance but will heat up a lot not only the motors but the battery's too!!

what size is the cruiser?

36", 48"? bigger? for either of these sizes a 700 would be more then adequate to obtain a nice plane 800 would achieve it better.

if your going to use twin props

possible use twin 600's twin 700 or 800 ''MIGHT'' be a tad insane and very unstable on the water.

depends what you want to achieve i guess a nice smooooooooooooooth plane reasonable speed go with the 700 or twin 540's - outright speed go with the 800 or twin 600's maybe 700 if your sure you can control it

remember using 700 or 800 motors you may need a 40 amp esc check motor requirements but typically you looking around the 50 mark for 1 esc, 600's would normally need the 25 amp esc at 25 there abouts so if costs a deciding factor bare this in mind ...

also if your using twin props and rudders u will want to concider the use of a v tail mixer to help with turning (actions P40c).. adding a further 27 to the budget...

check out actions website for details on esc's mixers etc...

I would personally recommend Action Esc's and mixers or for the twin prop and mixer system Actions P94 that does all the jobs in one go ... but at a cost of 78 and only can take 20A so your limited to max of twin 540's ( please correct me if im wrong there)

http://www.action-electronics.co.uk/mixers.php
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Dekan

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Re: what brushless motor would replace a brushed 700 motor
« Reply #2 on: August 05, 2010, 07:42:19 AM »

Thanks for the info... 36", or there abouts, cabin cruiser ...single motor.... not too interested in speed. As it's just required to trundle around a smallish pond, as its owner's eye sight is not great..

It's a shame that there is so little info out there on boat brushless motors....No such problems for model airplne guys...
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FullLeatherJacket

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Re: what brushless motor would replace a brushed 700 motor
« Reply #3 on: August 05, 2010, 07:57:15 AM »

I would personally recommend Action Esc's and mixers or for the twin prop and mixer system Actions P94 that does all the jobs in one go ... but at a cost of 78 and only can take 20A so your limited to max of twin 540's ( please correct me if im wrong there)
http://www.action-electronics.co.uk/mixers.php

OK!
Firstly, that 20A figure is for each motor, not the total current for the unit. We have several customers who use 12v Speed 700 motors with the P94, and a few who use MMB900 motors (Speed 900 equivalent). We also have one customer who has a 1/12 Severn lifeboat with two MMB900 motors and a P94 which he runs on 24 volts! Ref the cost, just price up two 20A ESCs and a proper marine motor mixer and then see which is the most expensive option. Like they say, 800+ customers can't all be wrong  :-))
In answer to Dave's original question about a brushless equivalent, I've made a comment on the other thread about this model. I hope it's of some use to him.
FLJ
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steamboatbob

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Re: what brushless motor would replace a brushed 700 motor
« Reply #4 on: August 05, 2010, 08:38:24 AM »

easy way to figure out what motor will suit

find out the rpm of your speed 700 motor

then divide that number by your battery voltage

then look for a motor with a KV value close to the results

eg

graupner speed 700 Race = 19,000 rpm

if you were running 7.4 V

19000/7.4 = 2567

so you would look for a brushless motor with a KV of 2567

Hope this helps

Cheers

BOB
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nick_75au

  • Guest
Re: what brushless motor would replace a brushed 700 motor
« Reply #5 on: August 05, 2010, 11:44:07 AM »

Speed 700 TURBO   9.6v      4.8-14.4v   15000   1562 Kv
Speed 700 BB TURBO   9.6v      4.8-16.8v   13000   1354 Kv
Speed 700 RACE     9.6v      7.2-9.6v           19000   1979 Kv
Speed 700 BB TURBO   12v      7.2-19.2v       11600   966 Kv

Kv is a constant, it does not change with voltage ok2

Nick
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Proteus

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Re: what brushless motor would replace a brushed 700 motor
« Reply #6 on: August 05, 2010, 01:02:28 PM »

bigger motors faster they go :) I'm currently building a huntsman cabin cruiser that will run twin props i will be working up to twin Graupner 800's but will start with my current spares 2 540's.
difference betwee brushed and brushless motors is that brushed motors offer better performance but at a price to regular brush replacements at cost 5 a set for good quality.

Brushless well thats answers itself good all round motors less maintenance but will heat up a lot not only the motors but the battery's too!!

what size is the cruiser?

36", 48"? bigger? for either of these sizes a 700 would be more then adequate to obtain a nice plane 800 would achieve it better.

if your going to use twin props

possible use twin 600's twin 700 or 800 ''MIGHT'' be a tad insane and very unstable on the water.

depends what you want to achieve i guess a nice smooooooooooooooth plane reasonable speed go with the 700 or twin 540's - outright speed go with the 800 or twin 600's maybe 700 if your sure you can control it

remember using 700 or 800 motors you may need a 40 amp esc check motor requirements but typically you looking around the 50 mark for 1 esc, 600's would normally need the 25 amp esc at 25 there abouts so if costs a deciding factor bare this in mind ...

also if your using twin props and rudders u will want to concider the use of a v tail mixer to help with turning (actions P40c).. adding a further 27 to the budget...

check out actions website for details on esc's mixers etc...

I would personally recommend Action Esc's and mixers or for the twin prop and mixer system Actions P94 that does all the jobs in one go ... but at a cost of 78 and only can take 20A so your limited to max of twin 540's ( please correct me if im wrong there)

http://www.action-electronics.co.uk/mixers.php

can I ask where have you got your information about brushed motor out performing Brushless motors ? because they don't, brushless are far more efficient.they are also just as cheap these days go in giant cod and look at the brushless on there and speed controllers yow will get bout 20% more power for the same price and same power usage.
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steamboatbob

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Re: what brushless motor would replace a brushed 700 motor
« Reply #7 on: August 05, 2010, 01:58:22 PM »

Speed 700 TURBO   9.6v      4.8-14.4v   15000   1562 Kv
Speed 700 BB TURBO   9.6v      4.8-16.8v   13000   1354 Kv
Speed 700 RACE     9.6v      7.2-9.6v           19000   1979 Kv
Speed 700 BB TURBO   12v      7.2-19.2v       11600   966 Kv

Kv is a constant, it does not change with voltage ok2

Nick



Yes but if you know how to apply the formula and find out what the rpms are that you need then you can get comparable brushless motors  as brushless motors are sold with a KV rating or RPM/V just make sure that you know what the amps are that the motor draws and get a good esc
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Dekan

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Re: what brushless motor would replace a brushed 700 motor
« Reply #8 on: August 05, 2010, 02:27:23 PM »

With model aircraft... we have a basic formula of a 100W per pound of All Up weight (AUW) this includes battery...This is good for most sport flyers/gliders.

I just figured that there would be some kind of  similar rule of thumb for boats 
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Prophet

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Re: what brushless motor would replace a brushed 700 motor
« Reply #9 on: August 05, 2010, 02:41:41 PM »

i used to race rc cars years ago at compteition level .. i always found that a brushed 20 turn motor would pound a similar car running a brushless 20 turn. thin g to remeber is that .. a brushless motor will heatr up the batterys .. a burshed motor wil lheat up itself and expand slightly freeing up the motor more giving you a better rate or rpm hence go faster :)

however i do stand to be corrected if im worng im wrong... but that what i was TAUGHT .....
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Dekan

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Re: what brushless motor would replace a brushed 700 motor
« Reply #10 on: August 05, 2010, 06:19:32 PM »

Not my in my experience brushless motors, when used in model planes are much more efficient than brushed motors...Brushed motors are only used in ready to fly or beginners model plane kits nowadays 
 
All the fast boat guys are using brushless in their racers.... so I guess this applies to boats..
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Proteus

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Re: what brushless motor would replace a brushed 700 motor
« Reply #11 on: August 05, 2010, 07:27:38 PM »

i used to race rc cars years ago at compteition level .. i always found that a brushed 20 turn motor would pound a similar car running a brushless 20 turn. thin g to remeber is that .. a brushless motor will heatr up the batterys .. a burshed motor wil lheat up itself and expand slightly freeing up the motor more giving you a better rate or rpm hence go faster :)

however i do stand to be corrected if im worng im wrong... but that what i was TAUGHT .....

so all the RC car boys have gone over to brushless motors so they can go slower ?

brushless motors are more efficiency subsequently you can use more power to go faster (bigger prop) for the same power used.
the closer the com to the magnets the better it is
HOT MAGNETS KILL THE SPEED OF THE MOTOR.
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iDENTITi

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Re: what brushless motor would replace a brushed 700 motor
« Reply #12 on: August 05, 2010, 07:34:22 PM »

I run a 24" FE jet boat with a 540L feigao motor.  I'm thinking probably a low-ish kv 540 short would do the trick, though I'd be tempted to go for the 540L or even XL depending on what size prop you're running, how many blades, etc.  And what voltage are you running at?  As for speed controller, I'd go for Hobbywing 35 or 90, depending on what voltage you run at really as to how many amps you need.  Brushless motors are inherently more effeciant if you run them size-for-size with a brushed.  My jet boat runs about 20-40mins on a 7.2v 4700 nimh pack just as an example.  It was specced to run on 11.1v LiPo, but have not got around to running it on them yet.
Hope this helps a bit.
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Dekan

  • Guest
Re: what brushless motor would replace a brushed 700 motor
« Reply #14 on: August 05, 2010, 10:51:32 PM »

boats with a big steam prop

Whats a steam prop?
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Proteus

  • Guest
Re: what brushless motor would replace a brushed 700 motor
« Reply #15 on: August 06, 2010, 12:20:44 AM »

big pushy props look on prop shop, you can get away with just a large bladed prop , but brushless motors with low KV have bags of power and to utilise this with lower revs (so less volts) you use a big bladed prop with a lot of pitch

Proteus
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tiggy_cat

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Re: what brushless motor would replace a brushed 700 motor
« Reply #16 on: August 06, 2010, 01:14:13 PM »

Hi,
 I asked the same question of Allan at Astec.  He recommended a Feigao 540L 13 motor with a 37mm prop as a starting point.

Got one on order but not arrived as yet. This is for a Challenger 31" hull. As I already have a similar boat with a 700BB running on 14.4v nimh pack, the comparison should be interesting.  That uses a Hughey mechanical 3 speed esc.   

Will be visiting Giant Cod for a brushless ESC for the new one
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Dekan

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Re: what brushless motor would replace a brushed 700 motor
« Reply #17 on: August 06, 2010, 05:37:10 PM »

Hi guys I posted almost the same question over on the RCG Boats forum... the answers were very sparse and nothing really useful was said ...I thank you for all your help but:-Obviously any boat brushless motor info is on a need to know basis... as I have had very little response since I posted the question.. My take on the situation some what tongue cheek is...

That either model boat builders know very little about brushless motors or they are just not telling :D

If posted a similar question about brushless motors for airplane, on an aiplane forum, I would have to beat the replys off with a stick...:)

It's a shame but it doesn't help the view that most boaters are a bit stuck in the past and not quite up to speed compared with the car and plane guys... :o   ;)

Thanks Proteus for the Prop Shop info looks very interesting
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iDENTITi

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Re: what brushless motor would replace a brushed 700 motor
« Reply #18 on: August 06, 2010, 06:20:41 PM »

Hi guys I posted almost the same question over on the RCG Boats forum... the answers were very sparse and nothing really useful was said ...I thank you for all your help but:-Obviously any boat brushless motor info is on a need to know basis... as I have had very little response since I posted the question.. My take on the situation some what tongue cheek is...

That either model boat builders know very little about brushless motors or they are just not telling :D

If posted a similar question about brushless motors for airplane, on an aiplane forum, I would have to beat the replys off with a stick...:)

It's a shame but it doesn't help the view that most boaters are a bit stuck in the past and not quite up to speed compared with the car and plane guys... :o   ;)
Thanks Proteus for the Prop Shop info looks very interesting

I'm probably going to get slated for this, but I think you're pretty much right there... Brushless is the way to go (unless you're on a budget)...
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Dekan

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Re: what brushless motor would replace a brushed 700 motor
« Reply #19 on: August 06, 2010, 07:04:25 PM »

Even on a budget theres very little excuse.... http://www.giantcod.co.uk/boat-stuff-c-224.html
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Dekan

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Re: what brushless motor would replace a brushed 700 motor
« Reply #20 on: August 09, 2010, 07:35:21 PM »

 I posted a similar question about brushless motor on RCG............. this was one of the responses. I dont know if anybody else would find this interesting   http://www.rcgroups.com/forums/showatt.php?attachmentid=3402635&d=1281223672
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mattycoops43

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Re: what brushless motor would replace a brushed 700 motor
« Reply #21 on: August 09, 2010, 11:38:26 PM »

I don't think people are being unhelpful on purpose. Aircraft have used brushless motors for years, so there is a general bit of understanding about standard sizes as equivelent for an ic engine. I don't think they are currently as well used in boats, so there is no benchmark. They are excellent for boats, but what type you want will totally change with what speed/type of boat you want.

A good way to compare to motors is to look at wattage. I don't know what watts a brushed motor produces, but most brushless motors are sold with a watt rating. it is a given that you will get a massive power jump with brushless motors, so you can go much smaller than the brushed motor you were using and still get more performance.

Small Outrunner motors, generally go down to approx 1000Kv, which is ideal for boats. They can't really be water cooled, but don't run hot anyway, unless your drawing too much current through it. if you want lower Kv again, it only comes with BIG motors, the washing machine equivalent ones will go down to 300 kv or lower, but are so powerful they would be complete overkill, and also be expensive.

Inrunners typically go from 2000Kv up to silly figures, and are easier to water cool, hence being ideal for high speed boats, they will run equivalent to a good ic engine. But no good for scale stuff unless you want to use a gearbox.

handy hint, Brushless motors are usually given  a nunmber which equates to size, so a 3612 will be 36mm dia and 12mm long (a pancake motor) while a 4652 will be 46mm dia and 52mm long.

It's only a rough guide but I would say a 540motor is less powerful than something like this

http://www.rctronics.co.uk/power-hd-hd283012-brushless-motor-980kv-662-p.asp

Hope that helps
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Dekan

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Re: what brushless motor would replace a brushed 700 motor
« Reply #22 on: August 10, 2010, 09:04:18 PM »

Thanks Matty.. Lots of info, but all of kinda vague nature... as there isn't enough sport users to provide a decent pool of info

What we have so far is a big low Kv outrunner is ok. That in it's self is not very helpful as a low Kv version can be available fo some quite small wattage motors ...

Nobody, it seems, can say what the wattage should be for different hull sizes...Maybe the only way currently is to relate the motor to the various different IC motor sizes... there has been some work here in the model aircraft crowd....
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mattycoops43

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Re: what brushless motor would replace a brushed 700 motor
« Reply #23 on: August 11, 2010, 03:26:22 PM »

I know brushless motors, but I am very new to boats, that is why I am a bit vague! I think some of the guys on here who know what they are doing will be able to give much more precise info. If we can get an expected power useage in watts, or Amp draw, we can narrow down motors.

Don't forget though, it is vague because the end use is vague. Any boat can have a tiny motor and put put round, or have a monster and fly round like a jet boat. Whether it looks right or wrong is another question.

You need to know what you want, if it's speed, then it's down to cost as the faster you go the more it costs, if cost is the issue, get the most power for your buck, if it's scale, you want to know the correct speed and the right sort of prop, from one of our "friendly experts"

There is no such thing as the "right motor" for a certain hull.
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DickyD

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Re: what brushless motor would replace a brushed 700 motor
« Reply #24 on: August 11, 2010, 04:16:14 PM »


You need to know what you want, if it's speed, then it's down to cost as the faster you go the more it costs, if cost is the issue, get the most power for your buck, if it's scale, you want to know the correct speed and the right sort of prop, from one of our "friendly experts"


Sarcasm ?  {:-{
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Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk
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