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Author Topic: battries & motor setup?  (Read 1959 times)

regiment

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battries & motor setup?
« on: September 23, 2011, 04:14:40 PM »

helping a young lad with his 28 inch  fire boat i have a couple of 7.2 nicads i am going to let hin have how long would a 6 volt motor last medium speed on them  the  hull is made of wood   thanks  regiment
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Shipmate60

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Re: battries @motor
« Reply #1 on: September 23, 2011, 04:25:05 PM »

It depends on the motor/prop set up.
Does he want a fast boat (Then it won't be long) or a slower boat which will last longer.

A 540 on a 30 mm prop will a short time.
A low drain 540 a lot longer.

It depends on the capacity and condition of the batteries.

Bob
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regiment

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Re: battries & motor setup?
« Reply #2 on: September 23, 2011, 07:10:09 PM »

hi bob it has a 20mm two bladed prop i have two 7,2 battries the young lad said as long as it goes so thanks gordon
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malcolmfrary

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Re: battries & motor setup?
« Reply #3 on: September 24, 2011, 10:08:50 AM »

It should go well.  With a small prop like that, the motor should survive with no problems, but tell him about oiling the shaft.
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justboatonic

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Re: battries & motor setup?
« Reply #4 on: September 24, 2011, 11:27:36 AM »

At full chat, a new 7.2v pack powering a typical 540 27 turn motor should give runs of between 5 to 7 minutes. At half chat or less, expect to get 12 minutes or so. If the packs are old and well used, you'll probably get 5 minutes runs out of them at moderate (chat) speed.

Of course if the weather is cold, this tends to reduce run time too.
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regiment

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Re: battries & motor setup?
« Reply #5 on: September 24, 2011, 11:46:58 AM »

getting a bit iffy now how about a 9.6 nicad or 6 volt 4 amp 
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malcolmfrary

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Re: battries & motor setup?
« Reply #6 on: September 24, 2011, 06:38:56 PM »

getting a bit iffy now how about a 9.6 nicad or 6 volt 4 amp 
9.6, fairly soon, a dead motor.  6 volts, less performance, probably still adequate, much more run time.  A lot still depends on the type of motor.  A 540 with two turns of baling wire and rare earth magnets and very close clearances will perform differently to one with  several dozen turns and weak magnets and plenty of clearance.  The type of hull makes a difference as well, as does the weight and shape of the model.  Its a launch, presumably, but is it nearer to a tug or a racer?
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regiment

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Re: battries & motor setup?
« Reply #7 on: September 24, 2011, 07:10:53 PM »

evening all it is a fire boat?? very light made of balsa wood i am making the top out of very thin ply  how about the 6 v 4 amp battery should have keep my mouth shut on this one
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Netleyned

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Re: battries & motor setup?
« Reply #8 on: September 24, 2011, 07:35:00 PM »

SLA will be much too heavy to give any performance
Look at using NiMh 7.2 or similar in that size of hull

Ned
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nick_75au

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Re: battries & motor setup?
« Reply #9 on: September 24, 2011, 08:56:02 PM »

You will get more runtime out of the 20 mm prop than a larger prop , The current will also depend on the RPM of the motor, a slower motor will draw less but at the expense of speed. Have you got any specs. of the motor?

Nick
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justboatonic

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Re: battries & motor setup?
« Reply #10 on: September 24, 2011, 09:04:11 PM »

getting a bit iffy now how about a 9.6 nicad or 6 volt 4 amp 

A 6v 4amp SLA will give lots of sailing time. My Drumbeat of Devon runs two MFA geared motors on a 6v 4amp SLA. Speed is moderate (very scale like imo) and I can sail her for a good 30 - 40 minutes with plenty of juice to spare.

However, Im either going to fit a 12v 4.5a nimh cell pack to give more speed or sell Drumbeat on, havent decided which yet.
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regiment

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Re: battries & motor setup?
« Reply #11 on: September 25, 2011, 02:21:02 PM »

thanks to all members who are trying to sort my motor problems out the.. boat empty is 1 1/2 kg with a 6 volt battery is 2 1/2 kg when finished about 3 kg   so far cost is nill scrounged wood and paint from local builder  have rx tx  if any body has a motor and rudder will swap new 12 volt 7 amp for post only or if you look on sales a battery charger @three batteries nicad  post only
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regiment

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Re: battries & motor setup?
« Reply #12 on: September 25, 2011, 02:23:37 PM »

photo of boat no plans only a photo so not to scale

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