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motor madness!

Old 05-31-2007, 09:38 PM
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Default motor madness!

OK...After years of glow and gas planes now Electrics have me excited with the new more powerful more affordable motors, ESC's, lipos, VPP, and ultralight airframes. But nothing is standardized at all. I have an electronics degree, I understand watts p/i.e etc. but am very confused about inrunner / outrunner except maybe the mechanical advantage of the rotor being larger and more poles on an outrunner. But how is it determined what prop for what motor and thrust produced. I assume (dangerous) that a lower kv # will produce more torque than a higher kv motor I also assume an outrunner produces more torque than an inrunner. So there must be more to figuring POWER than WATTS and how does THRUST get calculated. I also understand how gear reduction increases torque but there must be a point of deminishing return as an extreme a 1000:1 gearbox would have tremendous torque but wouldn't move enough air fast enough to fly anything even with a 6 foot prop. So is there a formula to figure thrust/prop/given watts, gearing. say a 200 watt motor turns a 10:4 prop giving 30 oz of thrust with a 2:1 gearbox would it be capable of giving 60 oz of thrust? minus the extra friction.How would you figure the new prop size? giving a 2:1 gearbox in theory would it not turn a 20:4 prop in theory?. Shurley not.
Probobly to many confusing questions here but I will take as many answers as you can give. I look at axi motors WHY SO MANY MODELS I AM TRULY CONFUSED.
Baisically my question is how do you calculate thrust given info on the motor spec sheets, KV, max constant current, and voltage (watts) and how will gearing effect thrust and how can you determine prop size/pitch. Or do you have to buy them all with an assortment of props and gearboxes and mount them to a thrust meter.

Thanks Todd V

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