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Is there a simple way?

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Old 02-13-2007, 09:48 PM
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propnut30
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Default Is there a simple way?

I'm new to electrics and I have bought a speed control and motor, but I have had little sucess. I dont blame the equipment, rather my judgment. It cost me a motor. Is there a simple way to decide what motor, speed control and battery combo I need? I can't quite grasp hot to make a selection. Here is what I have now. I have an ElectriFly SS-45, 45 AMP Brushless control, Good for 500 watts, an E-Flite Six series 2000kv motor (good for up to 26 amps and 300 watts), and a 9.6v battery (good for a paper weight). The battery will be replaced with a 3 cell LIPO. I got a hirger amp controller because I figured it would offer some protection from burining it out. Problem is now the motor is worth more than the contorl. I can solve this with a fuse though.

How do I decide if I need a gear box, or direct drive?

How do I decide on the prope size?

With all of the above installed the plane weighs about 24 oz. Has a wing area of 560 SQ inches. 51" wing span. It is a box wing like a stratos. See the thread (Please Help) in the Foamies forum. I'm getting frustrated with electrics and am seriously thinking about going back to glow. But because of noise restrictions I would have to go across town to fly.

Are there some guidelines that are set out in simple terms?


Brian
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Old 02-14-2007, 03:53 PM
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Fliprob17
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Default RE: Is there a simple way?

Electric flight is generally rated in terms of watts per pound of aircraft when talking about performance. For unlimited performance you are looking around 150 watts per pound. For good aerobatic performance, somewhere around 100-125 watts per pound. The way I do it is to look at the flying weight of the plane = 24 oz in your case = 1.5lbs, and then figure out total watts for unlimited performance 1.5lbs x 150 watts per lb = 225 total watts of power required. Now find a motor that is capable of delivering that. If total watts is not listed for the motor, take the amps the motor draws on a continuous basis, and multiply by the voltage supplied to the motor to get watts.

If you are looking at a 3 cell LiPo = rated at 11.1 volts, it actually hits 12.6 when fully charged and 9.9 volts when empty. So a median voltage would be 11.25 volts. Take the 225 total watts of power and divide by the 11.25 median voltage and you get 20 amps. So to have unlimited performance at all times, you would need a motor capable of 20 amps continuous, while accepting/capable of a 3 cell LiPo.

Now this is a lot of power on a continuous basis, I like to have unlimited performance when I get up to about 80% throttle. but it is a starting point.

Hope it helps
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Old 02-14-2007, 05:26 PM
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propnut30
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Default RE: Is there a simple way?

Thanks Fliprob17. It sounds like I have the right Spd Control and motor. 45A on the cont and 26 continuous on the motor. The watts are rated for 300. I just have to pick the prop. I will use the ones recomended by the manufacturer. If it dosent work out well than I will try a gear box.

Thanks a bunch
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