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Author Topic: hot motors  (Read 8230 times)

portside II

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hot motors
« on: August 22, 2009, 05:54:30 pm »

The SDM tug i have been building is going fine except--
http://www.modelboatmayhem.co.uk/forum/index.php?topic=18556.msg183732#new
After a couple of runs on the pond i found that the 6v motors were realy hot running on 12v through two electronise fr15 esc's , so i changed them to two 12v 540's and guess what they still run very hot but i dont have the power that i did with the 6v motors , i have a pair of 4 blade brass 50mm props and was wondering does anyone have any sugestions ? .
daz
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stallspeed

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Re: hot motors
« Reply #1 on: August 22, 2009, 05:59:33 pm »

12 volt 540s on 12 volt with 30mm props
or 6 volt 540s on 6 volt with 30mm props
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FullLeatherJacket

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Re: hot motors
« Reply #2 on: August 22, 2009, 08:43:01 pm »

i have a pair of 4 blade brass 50mm props and was wondering does anyone have any sugestions ? .
daz

That'll be the problem, Daz. You have the model equivalent of a Mini engine connected directly to a tractor wheel.
The props are too big for direct-drive 540s, which rev far too fast for them, so the motors are being worked too hard and so get hot (wouldn't you?).
Fit a pair of 720 Torque motors on 12v, or fit gearboxes onto the 540s. Either those or, as Mr Speed suggests, fit smaller props. My rule of thumb for d/drive says the props should be no larger in diameter than the motor case.
Works for me.
Suit yourself.
FLJ
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nick_75au

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Re: hot motors
« Reply #3 on: August 23, 2009, 04:50:59 am »

Dare I suggest maybe some high turn motors such as the rock crawler builders use 55, 65, 75 turns, sometimes known as commutator lathe motors in the Buggy world
Nick
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stallspeed

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Re: hot motors
« Reply #4 on: August 23, 2009, 05:15:53 am »

More turns means higher voltage,not necessarily more torque.
A 555 would be just shy of 60 turn motor with about 70% more torque.
That would be a marginal improvement meaning 40 mil props could be used.
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nick_75au

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Re: hot motors
« Reply #5 on: August 23, 2009, 05:52:13 am »

The buggy high turn motors are designed for 7.2 volts, they are designed for low rpm, not higher voltage. Spinning the props slower will reduce the current .
Or Dumas do a six volt motor that is reputed to spin 75 mm props with ease.

What voltage are you using?

 FLJ's rule of thumb is sound.

Me, well a couple of low KV brushless motors would work ;D

Nick
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stallspeed

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Re: hot motors
« Reply #6 on: August 23, 2009, 05:59:25 am »

Well seeing as they are 35mm props should work well then :}
Nick
You noticed too! :}
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nick_75au

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Re: hot motors
« Reply #7 on: August 23, 2009, 06:10:22 am »

I edited because in the original thread they were 35's, now they are 50mm brass, according to this thread (where's the confused emoticon?)


Nick
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stallspeed

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Re: hot motors
« Reply #8 on: August 23, 2009, 06:55:11 am »


What voltage are you using?
12 volts.
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portside II

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Re: hot motors
« Reply #9 on: August 23, 2009, 07:12:45 am »

Hi guys , i was using 35mm plastic race props in the first place when i was doing trials but as they were more efficient in one direction than the other and due to the wat the the drives are setup i decided to replace them with brass.
looks like bigger motors are required
daz
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stallspeed

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Re: hot motors
« Reply #10 on: August 23, 2009, 07:28:11 am »

Not bigger motors.Motors with greater torque
or reduction gears/pulleys or smaller props.
Take your pick.
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nick_75au

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Re: hot motors
« Reply #11 on: August 23, 2009, 07:41:50 am »

Oh I missed that as well :embarrassed:
It s not a race boat so I would try the 12volt motors on 6 volts as a trial, it may just work, half the RPM, 1/4 the power but the motor wont be trying to spin the props at ridiculous rpm. They definitely wont get hot :}
Nick
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portside II

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Re: hot motors
« Reply #12 on: August 23, 2009, 02:52:45 pm »

That's what i meant , if it was just the case of fitting bigger motors i have a pair of fast reving 900's on the shelf , but i would probably run them too hard and set fire to the boat.
I am just deliberating the following:-
higher torque motor's with the 50mm prop's
same motors with new 30mm prop's
same motors with gear's and 50mm prop's
There is probably a few more configurations , but dont want to make it too complicated  %% .
daz
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Rubdown

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Re: hot motors
« Reply #13 on: August 23, 2009, 03:17:51 pm »

Why not try a Pair of MMB 900 series motors,having seen them in action on various boats from Tugs to Stav's looney Mtb and they will easily throw your props with ease.
Make your own mind


Rubdown
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malcolmfrary

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Re: hot motors
« Reply #14 on: August 23, 2009, 08:44:17 pm »

A 540 was being used in a situation where a 545 would have been more appropriate.  More poles (5 rather than the 3 of a 540), more torque, less RPM, the motor not being forced to low RPM by the load imposed by the prop.
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stallspeed

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Re: hot motors
« Reply #15 on: August 23, 2009, 10:28:21 pm »

A 540 was being used in a situation where a 545 would have been more appropriate.  More poles (5 rather than the 3 of a 540), more torque, less RPM, the motor not being forced to low RPM by the load imposed by the prop.
That's similar to what the rep at chart hobbies used to say.
I believed it myself until I tested a pair.
mabuchi 545
mabuchi 540
http://www.mfacomodrills.com/motors/540-1.html

You do come across the odd high torque 545s but you also get high torque 540s.
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malcolmfrary

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Re: hot motors
« Reply #16 on: August 24, 2009, 10:40:52 am »

The figures in the links indicate that the 5 pole motors are slower revving with more torque and generally lower current consumption than 3 pole motors.  Just what is wanted for a tug, and most other dispkaacement hulls.  It is possible to have a different wind on a 3 pole motor to take it into 5 pole performance territory, and vice-versa, but it will always be a second best choice because of the underlying physics.
It is a sort of convention that a 540 is a 3 pole motor with a case length of 54mm, and a 545 is a 5 pole motor in the same size case.  There is, sadly, nothing to stop any manufacturer ignoring the convention, and has probably happened.  The recent trend by manufacturers of creating "new" series' of motors by rounding up (400s, 600's) does nothing to help cut the confusion, neither does the habit of some modellers of rounding down (300, 500 etc).
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stallspeed

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Re: hot motors
« Reply #17 on: August 24, 2009, 04:25:33 pm »

And yet it looks like the 540 from this sourcewould be a better than the listed 545 when a prop is oversized.
Confusion abounds.
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portside II

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Re: hot motors
« Reply #18 on: August 24, 2009, 10:07:49 pm »

I think i have it sorted with the help from NMM/FLJ , a pair of 755's are at this very moment zooming up the country in the back of a royal mail van/lorry/whatever to me and once i have built the new mounts i shall once again have some more fun .
updates to follow.
daz
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Marks Model Bits

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Re: hot motors
« Reply #19 on: August 24, 2009, 11:53:48 pm »

Who's this NMM then? <*< <*< <*< <*<
National Maritime Museum? Nice Mess Maker? New Mist Maker?   {-) {-) {-) {-)
Think you mean MMB!!!!! I will let you off this time Daz.......... Isn't that a washing powder????? :P :P :P :P ;D ;D

Mark.
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OMK

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Re: hot motors
« Reply #20 on: August 25, 2009, 12:55:03 am »

NMM:

Not My Making
Never Melt Muffins
Nice Mule Mitts
Nautical Mile Meter
Nefarious Mischief Maker
Nicked My Models
Nifty Music Maker...

...or just No Mustang Mark, perhaps?

And then there was 'Tide', 'Surf', 'Omo', 'Vim', etc...................
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malcolmfrary

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Re: hot motors
« Reply #21 on: August 25, 2009, 10:05:38 am »

And yet it looks like the 540 from this sourcewould be a better than the listed 545 when a prop is oversized.
Confusion abounds.
From the link
540information
Quote
Performance
Operating v   : 4.5v - 12v
Nominal v   : 12v
No Load RPM   : 16800
No Load A   : 1A
Stall Torque   : 39.48 oz-in   278.8 mN-m
Stall Current   : 42A
Kt   : 0.94 oz-in/A   6.6 mN-m/A
Kv   : 1400 rpm/V
Efficiency   : 71%
RPM - Peak Eff   : 14525
Current - Peak Eff   : 6.6A
545 information
Quote
Performance
Model   M5-RS545-12
Operating v   : 5v - 15v
Nominal v   : 12v
No Load RPM   : 16800
No Load A   : 0.9A
Stall Torque   : 23.61 oz-in   166.7 mN-m
Stall Current   : 21A
Kt   : 1.12 oz-in/A   7.9 mN-m/A
Kv   : 1400 rpm/V
Efficiency   : 79.8%
RPM - Peak Eff   : 13920
Torque - Peak Eff   : 4.89 oz-in/A   34.5 mN-m
Current - Peak Eff   : 4.4A
What confusion? 
No load speed identical, but less current draw with the 5 pole. 
Torque, less with the 3 pole.
Stall current, more with the 3 pole.
The efficiency figure for the 3 pole is lower as well.  This means that more of the energy supplied is turned into heat.
Anyway, after advice, a good choice has been made and hopefully a happy ending is in sight.
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Marks Model Bits

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Re: hot motors
« Reply #22 on: August 25, 2009, 10:43:59 am »

...or just No Mustang Mark, perhaps?

Of course it is I must have been having a dim moment!!! :embarrassed: :embarrassed: :embarrassed:

Well it was late when I posted it and I had just spent 12 hours in front of my computer working on my new website, plus I had also had a few beers................. My god I am coming out with more excuses than Richard Hammond on a bad day now!!!!

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portside II

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Re: hot motors
« Reply #23 on: August 25, 2009, 12:48:09 pm »

And without any doubt of the man  the postie has just handed me a small box containing the new motors , :} .
Me one happy bunny  :-)) well i would be if i did'nt have to go out this aft and work tonight , so they will have to wait for fitting until wed eve or thursday .
THANKYOU MARK  :-))  :-))
daz
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portside II

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Re: hot motors
« Reply #24 on: August 27, 2009, 05:07:45 pm »

right the new motors have been fitted and are now awaiting water tests .
here is a link to the build post
http://www.modelboatmayhem.co.uk/forum/index.php?topic=18556.0
new mounts were made from some plate i had in the shed and these were connecetd to the hull base and lined up with the motors to the shafts

i also fixed the motors with screws , but as the access would be limited i threaded nuts on first and used them to tighten the screws down  :-))

this is a pic of the new motor against the old 540.
daz
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