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Author Topic: Burnt out motor  (Read 1951 times)

Temps

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Burnt out motor
« on: September 18, 2009, 04:46:13 pm »

Hi if you havent seen my sportboat post then ive tried her to day and had a problem with the motor burning out i thin im running a to bigger prop and over loading the motor but i havent got much experience with small motors so im open to advive .All looked good for a minute or two then it was like the battery was flat so i pulled it in for a look thinking i may have some weed round the prop but found smoke bellowing out   upon inspection it was the motor smoking out the vents ive not had much experience with these little motors but the speed control was cool the battery was cool just the motor burning hot and smoking ? i think maybe im running to bigger prop ? its deffinatley got a smooth alignment between motor and prop tube
The specs  im running are Graupner Speed 400 motor brushed direct drive to a 35mm x prop the speed control is a forward only Mtronics viper tempo 15 (run down to a 15turn motor) and a 7.2 nican 2000mha any ideas would be welcome obvs ill have to replace the cooked motor  but if it is the prop any ideas what this little motor will turn happily ok2
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malcolmfrary

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Re: Burnt out motor
« Reply #1 on: September 19, 2009, 01:36:54 pm »

Burnt motor = either too many volts and/or too much prop (diameter, number of blades, pitch, any combination).  Throw in having the shaft too tight as well then add the possibility that the motor might have been a bad 'un.
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"With the right tool, you can break anything" - Garfield

andrewh

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Re: Burnt out motor
« Reply #2 on: September 20, 2009, 02:43:04 am »

Hi, Temps

We can say with reasonable certainty that the prop was too much for the motor :}

All (good) S400s are capable of 10A continuous  - when welll cooled (as in the pointy end of an aircraft)

Having taken advice from George turner and others I use a Graupner racing 29mmm prop for direct drive with S400s, as used, I believe by the S400 racers,
I have also used a 3-bladed "30 mm" prop from SHG, but this distresses the Mtronics 15 after a few minutes.

So suggest:
 
  • you go with smaller prop (less than 30mm)
    Water-cool the motor (buy or make a cooling coil)
    Pick a soft S400.  You don't say which one you used but on a 7.2V buggy pack you could use a 7.2 V one or a 12V one (but not (as you have seen) a 4.8 or 6V version)

You could use a 5-pole version (385) reasonably safely with the same prop, but this might not give the performance you want.
andrew
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Temps

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Re: Burnt out motor
« Reply #3 on: September 20, 2009, 11:11:13 pm »

thanks for the replys the motor was a 400 7.2 version ive had a look and found another motor its and Mtroniks Vision 400
This high torque 380 sized Mabuchi motor comes complete with motor suppression capacitors.
Dimensions : L33.0mm, D28.0mm, Shaft diameter 2.3mm
Voltage, 12V
Off load current: 1.0A
Max current: 45A
RPM:12000RPM
with this prop 2 Blade Racing Propeller 25mm Right Hand M4
2 blades, of hi-impact plastic with precision brass insert. Pitch approx. 0.85 x prop , for high-revving engines.
Propeller 25 mm Pitch 21mm
and i had been running this Graupner Speed 400 7.2V (1794)
The Speed 400 has been developed because of the excellent performances of these small E-motors. They are ideal for direct drive power systems of model boats having one or several motors.
Nominal voltage 7.2V, Operating voltage range 3.6-8.4V
No-load rpm 162 Blade Racing Propeller 35mm Right Hand M4
2 blades, of hi-impact plastic with precision brass insert. Pitch approx. 1.6 x prop , for slow-revving engines.
Propeller 35 mm Pitch 56mm
400, Current drain at max. efficiency 3,3 A
Shaft diameter 2.3mm, Weight 73g
with this prop
2 Blade Racing Propeller 35mm Right Hand M4
2 blades, of hi-impact plastic with precision brass insert. Pitch approx. 1.6 x prop , for slow-revving engines.
Propeller 35 mm Pitch 56mm
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FullLeatherJacket

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Re: Burnt out motor
« Reply #4 on: September 21, 2009, 07:58:42 am »

I have the same type of Speed 400 motor in a 20" Fairey Swordsman, running a Prop Shop 1" dia (25mm) 2-blade prop on 6 x AA cells. Goes like greased weasel pooh and doesn't get excessively hot - it's not even water-cooled.
A 35mm prop is WAY too big for an ungeared 400 motor. The phrase "for low-revving engines" should have given you a huge hint. The actual spec for the 7.2v Speed 400 at its nominal voltage is 16400 RPM (I guess that bit of your posting was a typo) and that is NOT low-revving. A good general rule of thumb for direct-drive is not to use a prop whose diameter is larger than that of the motor case.
I've no experience of the MTroniks motor but, bearing in mind the low price of these things, I'd recommend sticking to the Graupner one. I found one for 7.45 without even looking for a better price elsewhere
Suit yourself; works for me.
FLJ
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