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Old Aug 04, 2009, 06:08 PM
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5000KV Motor?

Hi guys

...I am thinking about to try a 5000KV motor on the CX200, or is 5000KV to high?

best regards Georg
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Old Aug 04, 2009, 06:48 PM
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United States, AZ, Mesa
Joined Jul 2007
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Quote:
Originally Posted by fire113
Hi guys

...I am thinking about to try a 5000KV motor on the CX200, or is 5000KV to high?

best regards Georg
It's all about gearing... with the right pinion, you'll still have about the same head speed.

The trade-off if the motors are about the same size, is that a lower kV will have more torque - still, that is affected by the gearing.

If you take a 5000kV motor and you put it on a 10:1 gear ratio, you're only getting about 500kV, which on 11.1V would translate to 5550 head speed... much too high. So you would need whatever pinion gear would get you to about a 15:1 or 16:1 gear ratio, which would put you in the 3500 range for head speed. It's all a numbers game.
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Old Aug 05, 2009, 05:03 PM
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Hi Jasmine,

...was not sure and my english is not good enought

In front of me I have here a Kontronik-Micro-Dancer with 2800KV and a 10 pinion gear.
I would like to use it on 11,1 Volt / 25A BL-ESC, so I will get 3108 head speed right ? Is 3500 the optimal head speed or is it the upper end for the head unit/blades ?
Have no other pinion gear here and I can not wait any longer would like to fly this small beast.

Motor will take about 9-13A and I think max. current was 18A(<-not sure)
~100-140 Watt (short 200Watt) is it enought power for this little heavywight to do good 3D flying ?


Best regards Georg







Quote:
Originally Posted by jasmine2501
It's all about gearing... with the right pinion, you'll still have about the same head speed.

The trade-off if the motors are about the same size, is that a lower kV will have more torque - still, that is affected by the gearing.

If you take a 5000kV motor and you put it on a 10:1 gear ratio, you're only getting about 500kV, which on 11.1V would translate to 5550 head speed... much too high. So you would need whatever pinion gear would get you to about a 15:1 or 16:1 gear ratio, which would put you in the 3500 range for head speed. It's all a numbers game.
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Old Aug 05, 2009, 05:36 PM
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I don't know for sure... but here's how you would figure it out...

Personally, I think around 4000 is good head speed for hard 3D on these little birds. Here's how to make an estimate.

(Volts X kV) X (pinion teeth / main teeth) = head speed (rpm)

11.1V X 2800 rpm/V = 31080 rpm (volts cancels out)

10 teeth / 120 teeth = 0.833333 (teeth cancels out)

So now you have...

31080 rpm X 0.833333 = 2590 rpm

Not even in the ball park of what you need. And the real head speed will be a little lower because of efficiency losses. You'll need a bigger pinion - 12T would get you up to 3108 rpm... really though, you probably need a faster motor.

Quote:
Originally Posted by fire113
Hi Jasmine,

...was not sure and my english is not good enought

In front of me I have here a Kontronik-Micro-Dancer with 2800KV and a 10 pinion gear.
I would like to use it on 11,1 Volt / 25A BL-ESC, so I will get 3108 head speed right ? Is 3500 the optimal head speed or is it the upper end for the head unit/blades ?
Have no other pinion gear here and I can not wait any longer would like to fly this small beast.

Motor will take about 9-13A and I think max. current was 18A(<-not sure)
~100-140 Watt (short 200Watt) is it enought power for this little heavywight to do good 3D flying ?


Best regards Georg
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Old Aug 05, 2009, 06:13 PM
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Joined Jun 2009
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...Yes I agree, that was the reason why I was thinking about ~4000-5000KV.

Thanks Jasmine for Your fast help so I will not finde out what will happen with 2590 rpm on the main head unit

...good N8...Georg.

Edit ...I tryed 3800KV with 12 pinion gear

Quote:
Originally Posted by jasmine2501
I don't know for sure... but here's how you would figure it out...

Personally, I think around 4000 is good head speed for hard 3D on these little birds. Here's how to make an estimate.

(Volts X kV) X (pinion teeth / main teeth) = head speed (rpm)

11.1V X 2800 rpm/V = 31080 rpm (volts cancels out)

10 teeth / 120 teeth = 0.833333 (teeth cancels out)

So now you have...

31080 rpm X 0.833333 = 2590 rpm

Not even in the ball park of what you need. And the real head speed will be a little lower because of efficiency losses. You'll need a bigger pinion - 12T would get you up to 3108 rpm... really though, you probably need a faster motor.
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Last edited by fire113; Aug 08, 2009 at 12:56 PM.
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Old Aug 13, 2009, 09:07 PM
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Canada, ON, Frontenac County
Joined Feb 2007
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The copterX 200 main shaft and tail shaft will just bend if you jump higer than a 3500 kv. Thats the main problem with this heli. Stick with the stock motor, and use it as a backyard circuit flyer...it will last for quite some time this way. Once you start messin with higher kv motors, thats when all these issues with bent shafts start to happen. Tierods start to break, and things just start messn up on you.
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Old Aug 13, 2009, 10:00 PM
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Yeah but you can just use a smaller pinion - it's not about the motor kV, you have to take the gearing into account.
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Old Aug 13, 2009, 11:13 PM
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ive found anything over 11t on a 3500 kv...will blast the head apart or tail apart.
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Old Aug 13, 2009, 11:17 PM
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Yeah too much head speed will do that. On most Trex blades there is a max head speed warning - 4200 rpm for the 250. I wonder what the max is for the CX 200 then?
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Old Aug 14, 2009, 02:28 AM
Team Mulikow 3D
Oxfordshire, UK
Joined Jan 2007
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Quote:
Originally Posted by jasmine2501
Yeah too much head speed will do that. On most Trex blades there is a max head speed warning - 4200 rpm for the 250. I wonder what the max is for the CX 200 then?
About 30rpm on the V1 shafts - the V2's you could get it up to about 40rpm

Actually it was really just over 3,000 rpm - there was a very definite cut-off, if I increased my TC by 2 or 3 points too high and pop - there goes the shaft
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