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what should i buy

Old 10-21-2010, 11:30 PM
  #1  
r4pt0r
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Default what should i buy

I am going to buy a GWS powersystem off of towerhobbies.com what gear ratio do i want to spin a 12 inch prop in a 4 foot plus wingspan plane. i want brushed motor, and im using a 3 cell lipo, 2200 mah 11.1 volts. any advice is great, thanks
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Old 10-22-2010, 03:44 PM
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soar-ne
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I will assume you are asking about the 400 size motor as the 300-350 size don't like 3 cell lipos much, the 300 will last a while on 3 cells if you prop and gear for a max of 5-6 amps.
The 400 is more robust and I have flown them on 3 cell lipos but you must keep the amps below 8 amps or they dont have too long a life.
For a starting point I would go with the "H" ratio (5.28 to 1) with a 12x6 prop. Have a Wattmeter?
Have to say this----------With the price of brushless nowdays, why do you want the brushed system Places like Headsuprc have some combos of 400 size outrunners that are almost as cheap as the GWS 400 and ESC and will last with 3 cells. Just get a low kv motor to swing a big prop....

Good Luck
Bob
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Old 10-22-2010, 03:59 PM
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Dr Kiwi
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If you want to use a brushed 400 on 3s then you are better off with a nominally 7.2v Speed 400 like this: http://www.hobby-lobby.com/speed_400..._2565_prd1.htm.... rather than a nominally 6v 400.

According to Bruce Abbott (http://homepages.paradise.net.nz/bha...IG400_72V.html) the GWS 400 is 2760Kv, while a MIG 7.2v 400 (is that the same as a Graupner 7.2v 400?) is only 2189Kv... lower Kv will be happier on 3s.

Motocalc lists the GWS 400 as 2785Kv, the Graupner 6v Speed 400 as 3097Kv and the Graupner 7.2v Speed 400 as 2332Kv


Whatever you get it will run on 3s as long as you keep the amps in check!
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Old 10-22-2010, 09:27 PM
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r4pt0r
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i dont get kv or any of that stuff. i have an esc that works with my battery and my motors. i build, i fly, i crash http://www.youtube.com/watch?v=VadAkBz2bJU
my construction techniques arent that durable http://www.youtube.com/watch?v=zmekm...os=xZsTItXlO3o but i just want to get out there and fly. my planes never last long enough to burn out a motor. but if some one would explain brushless to me, id appreciate it. i dont get the third wire on brushless, inrunner vs outrunner, brushed is easier for me to understand. and yes a 400
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Old 10-22-2010, 09:39 PM
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Insomniac
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With a brushed motor, you've got stationary magnets on the casing, and a rotating electromagnet on the shaft. As the shaft rotates, different points of the commutator rub against the brushes, which are wired to different sections of the electromagnet. As the shaft moves, so does the magnetic field on it so it is constantly being repelled by the permanent magnets. So the shaft spins.

The problem is, that the point where the brushes rub is inefficient and doesn't last very long. So with a brushless motor, the get rid of the brushes. So now you have the permanent magnets on the rotating bit, and the electromagnet is directly connected to the three wires (No brushes!). This means that if you just put normal DC through any two of the wires, the motor would rotate to align with a certain position, and then stop. Connect a different pair of wires, and the motor would rotate a few more degrees before stopping.

So, the brushless speed control serves to constantly change which pair of wires are being energized... which means the motor constantly spins. Rather than having the mechanical brushes switch the position of the magnetic field, brushless motors use the electronics of the controller to perform the same function.

An inrunner brushless motor looks basically like a normal brushed motor... there's a stationary 'can' which all of the bits are mounted within. Of course, the magnet is now on the shaft and the electromagnet's windings are on the inside of the casing, but for all intents and purposes they look like brushed motors (apart from the 3 wires of course!)

An outrunner brushless motor has the back of the motor open, rather than sealed off. And the magnets are on the casing this time, with the electromagnets mounted (with a bearing) on the shaft. The bit you attach to the plane is directly attached to the electromagnets. So this whole inner section stays stationary, while the shaft and entire casing rotates (hence the 'out' runner... the outside of it spins).

The basic difference in the use of inrunners and outrunners is that mainly outrunners have lower Kv ratings, while inrunners have higher Kv ratings. Kv simply means 'rpm per volt' and specifies how fast the motor should spin if one volt is fed to it, without a prop attached. As motors draw more amps the more you resist and hold them back, for large props you need to use lower Kv motors to keep the amp draw down. High Kv motors are used for faster spinning applications, like small props and EDF systems.

Which basically boils down to inrunners for speed, outrunners for torque.

Hope that makes sense.
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