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Author Topic: Graupner Speed 400  (Read 2487 times)

Davenotdone

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Graupner Speed 400
« on: November 20, 2012, 10:47:57 AM »

Hi everyone. I am still trying to get a correct size motor  for my Seaport tug. The problem is that my two young boys run it and as you might guess they have it ' flat out ' all the time. I am using a 6v 5amp gel cel type battery and have got the motor selection down to a Graupner Speed 400. This is a direct replacement for the original ( now burnt out ) 380 size motor. There are 2 400's to choose from. 7.2v (1794) which revs to 16,400 and the 6v one (3321) which revs to 18,000. The obvious choice ( because of my battery ) would be the 6v one but i was wondering for the sake of a  more relaxed engine and lower revs  if i put the 7.2v version in that it would reduce the revs and the motor would not be running at it's full speed because i am only giving it 6v. I am more after long run time and good ( not fast ) speed and i do realise it is not a planing type hull. What  i don't understand with this ' don't fit a prop bigger than the diameter of the motor' rule is that the tug originally came with a plastic 40mm 3 blade one, how could the original cheapo 380 motor run it? I have fitted a 3 blade brass 30mm scale type prop, new 4mm prop shaft and am open to any suggestions other than the Graupner you may have to fit a suitable 380 type motor and allso what would be the biggest size prop ( brass, 3 blade ) i could fit?  You may see on the Seaport part of the forum that this will be my 4th motor in this boat, is this a record??? As i am new to this hobby the Dickie tug has taught me a lot about model boats and i am happy to learn more! Any suggestions more than welcome ,this forum has taught me a lot!! Regards, Dave.
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malcolmfrary

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Re: Graupner Speed 400
« Reply #1 on: November 20, 2012, 09:50:20 PM »

Quote
What  i don't understand with this ' don't fit a prop bigger than the diameter of the motor' rule is that the tug originally came with a plastic 40mm 3 blade one, how could the original cheapo 380 motor run it? I have fitted a 3 blade brass 30mm scale type prop, new 4mm prop shaft and am open to any suggestions other than the Graupner you may have to fit a suitable 380 type motor and allso what would be the biggest size prop ( brass, 3 blade ) i could fit?  You may see on the Seaport part of the forum that this will be my 4th motor in this boat
Its not a hard and fast rule, more a solid guideline, and a lot depends on the actual motor.  The fact that you have done several motor changes probably backs this up.  Probably a 7.2, or higher, voltage 385 would be better, stick with the 30mm prop.  The arrangement moves my Snowberry quite indecently, should do much the same for a Seaport.
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nick_75au

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Re: Graupner Speed 400
« Reply #2 on: November 21, 2012, 06:20:59 AM »

The motor voltages on the Graupner motors are a nominal voltage, fast boats will put higher volts up their backside and scale boaters will put less in general. The voltage Graupner specify is more an indication of the Kv (RPM per volt) than the voltage required The 6 volt has a Kv of 3000, the 7.2 has a Kv of 2278, for the tug I would think a Kv of around 15-1700 would be better to give about 10000 Rpm for the 30mm prop, the 40 mm prop a RPM of 6-8000 Rpm is better so a 10-1200Kv motor.


I have data on a Mabuchi RE 385 or Mabuchi RE 360 that Have Kv ratings in a good range, the RE360 has a Kv of 1050 and the 385 has a Kv of 868 (good for the 40 mm prop) the Info have for the RE 380 is 3600 Kv (no wonder it burned out), Unfortunately non standard motor winds throw all of these figures out the window :o [size=78%]  [/size]


Nick

http://www.mfacomodrills.com/motors/385.html

http://www.mfacomodrills.com/motors/360.html
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Davenotdone

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Re: Graupner Speed 400
« Reply #3 on: November 21, 2012, 09:08:27 PM »

Thank you both for your replies. You have made the problem i have much easier to understand. I think i will go for the MFA 385, its's the same size coupling i allready have and i will stick with the 30mm prop 3 blade 'scale' i allready have and work my way up in prop size if i decide to. I note it is rated 6v - 15v ( i am running 6v ) but i guess that  this is the idea ie use a higher rated motor at a lower voltage? After running should the motor be hot / warm / cold ? I notice that the bracket that comes with the motor does not have holes in the front of it, would that effect the cooling? Do i  put in a car type fuse and if so what amps ( running an Mtroniks 15 Plug & Play ) Last question and i will leave you both in peace, does the motor come suppresed and if not do i have to? Once again may thanks for your help, i nearly gave up on this tug but with your help i ( and my two young boys ) will see it through to the end!!
    Regards, Dave ( and the boys )
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Tug-Kenny

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Re: Graupner Speed 400
« Reply #4 on: November 21, 2012, 09:13:46 PM »


Hi Dave,

Yes, you are going to need a fuse in the circuit, I would recommend starting at 10 amps, although I wouldn't expect the motor to get near this or get hot. A test in the bath first might be a good idea.

Cheers

Ken
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john s 2

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Re: Graupner Speed 400
« Reply #5 on: November 21, 2012, 09:41:28 PM »

If your motor has a built in fan the the front case holes should not be restricted. You could make a fan and soider it on to the Huco to blow air through the motor. This is the best way to cool a motor as the air acts directly on the armature. Kens fuse advice is spot on. Please remember that sometimes a smaller prop is better as it allows the motor to run in its rev range If the motor is getting hot and smelling then its being overloaded. John.
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john44

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Re: Graupner Speed 400
« Reply #6 on: November 22, 2012, 05:50:49 PM »

Hi davenotdone, I had a similar problem when I took my young grandson sailing
he only knows 1 speed, which is flat out forwards or reverse.
 when I got the boat back out of the water the battery was hot and you could use the motor as a cigarette lighter.
What I did was to make a disc out of plasticard with a smaller slot than the transmitter both for forwards and reverse and blue tacked it to the throttle stick recess thus
limiting the speed.It works, and he isn,t bothered about the loss of speed because
he can sail for longer now.

john
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