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Author Topic: motor plus battery and radio gear help please  (Read 1590 times)

cassf1

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motor plus battery and radio gear help please
« on: March 08, 2009, 11:15:43 PM »

Hi,
       Hello to everyone here, I'm new to this never built a RC before. what I'm hoping to build is a bait boat (used for fishing) i have the hull propeller and rudder in now i need to look at getting the electrics sorted, i was planning on using these parts as have them from various things motor 540 brushed, battery 6v 3ah lead acid, ESC not sure yet, TX and Rx not sure but would have to be 4 channel.

I'm wondering would an ESC be enough or would i need to put some sort of gearing in there as its torque I'm after not just speed, cause usual fish rivers.
Also would this battery power the Rx as well as i think i would need a large battery as would be carrying some weight.
Rx and TX 4 channel = motor, rudder and two hoppers for bait any ideas please.

Any help you guys can give me would be appreciated
Thanks Craig
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malcolmfrary

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Re: motor plus battery and radio gear help please
« Reply #1 on: March 10, 2009, 11:29:15 AM »

Provided the prop is not too big, with a displacement hull, it becomes self regulating.  A propeller in water is effectively a torque converter.  Just get one a bit smaller than the outside diameter of the motor, the motor spins the prop, the prop moves water backwards, the hull goes forwards.  To move the hull forward its own length, the prop has to move the same volume backwards, plus some for luck.  it doesn't really matter whether its a wide slow column of water that is moved, or a narrow fast stream, apart from the fact that the boat going forward cannot go faster than the water going backwards. 
Any river means moving water, you do need speed to overcome this.  As long as its not a silly racing motor, direct drive is fine and has the advantage of simplicity.
RC gear was originally designed to run on 6 volts as this was convenient for either 4 dry cells or 3 lead acid cells.
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Stavros

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Re: motor plus battery and radio gear help please
« Reply #2 on: March 10, 2009, 05:58:39 PM »

Having built a few bait boats in the past a 540 is not going to be powerfull enough on 6v what you really need is a graupener 720 which will swing a brass prop up to 31/5 inches but you will have to run 12v,With the flow of a river a 540 will not be able to cope with the weight of the hull and the bait another motor i would also reccomend is from No mustang mark on this forum see traders adverts


Stav
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cassf1

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Re: motor plus battery and radio gear help please
« Reply #3 on: March 11, 2009, 11:27:09 PM »

Hi all,
       Thank you guys for your help this has been very useful. If you have anymore advice it would be appreciated.
 
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cassf1

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Re: motor plus battery and radio gear help please
« Reply #4 on: March 12, 2009, 11:12:53 PM »

Hi all,

Thanks for replys

I think i will try graupner 900 with a 12v 12ah battery, my question now is what amp ESC will i need. Do i find out by wiring motor direct to battery and put a amp meter in the negative (return) circuit.

Also will this battery be too high to run the RX will i need to put a resister in now or something RX has a BEC built in.

What propeller will be best 2 or 3 blade.

Thanks Craig
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Stavros

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Re: motor plus battery and radio gear help please
« Reply #5 on: March 12, 2009, 11:19:12 PM »

Contact Action I know he has the right ESc for the Job.......FLJ on this froum see advert for Action in the traders sectiopn


Stav
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Marks Model Bits

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Re: motor plus battery and radio gear help please
« Reply #6 on: March 12, 2009, 11:34:59 PM »

Hi Craig, have a look at this motor, virtually identical spec to a Graupner 900 and alot cheaper too!!!!! http://www.modelboatmayhem.co.uk/forum/index.php?topic=14857.msg150248#msg150248

Give me a call you never know you might even talk me into giving a discount...............Possibly

Mark.
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malcolmfrary

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Re: motor plus battery and radio gear help please
« Reply #7 on: March 13, 2009, 10:20:23 AM »

FLJ is a firm believer that BECs are the invention of the devil, and that the best way is to use a separate RX pack of 4 AAs.  This works well.
The RX BEC is only intended for use with 6 cell NiCads and similar and should not be considered as suitable for 12 volt running.  Some ESCs have a built-in BEC, some require a separate one.  Its all down to personal choice and reading the specs where available.
To figure the rating of ESC needed, connect up the motor as you said, then put it under a load (big prop in a bucket of water, fiction strap on the shaft etc) and get a max reading.  Then add about 50% and look for the next available rating above that.
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cassf1

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Re: motor plus battery and radio gear help please
« Reply #8 on: March 13, 2009, 07:32:32 PM »

Hi,

Mark thanks for your reply unfortunately i have already ordered a graupner 900 and it should be here tomorrow. :(

Malcolm thank you for information just wondering what a friction strip is i thinking it may be used to stop the outer casing of the propshaft spinning. 

Also is there a rule of thumb to sort the size of propeller, or would it just be a case of try it.

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malcolmfrary

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Re: motor plus battery and radio gear help please
« Reply #9 on: March 13, 2009, 07:43:57 PM »

One method of applying friction is to grip the shaft with the fingers.  This gets a bit fraught, metal being stronger than skin..  A better method is to wrap a piece of string round the shaft, anchor one end and pull on the other.  Some like pliers with a bit of felt as a friction surface.  The idea is to make the motor work a bit harder than it would in service.  By doing that, the current draw will be increased, so the ESC selected will be more reliable.
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