KV, prop size and batteries - RCCanada - Canada Radio Controlled Hobby Forum
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Multi Rotor Discussion Tri's, Quad's, Hex'as and more. Discuss anything multi-rotor, including multi-rotor stabilization and FPV setups.

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Old 12-29-2012, 04:52 PM   #1
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I am: David K
Join Date: Oct 2010
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KV, prop size and batteries

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Looking for some theory 101. I'm familiar with calculators and power systems but am wondering what the performance differences are when you're achieving the same thrust different ways in a quad. (where the issues of prop size relating to ground clearance and torque roll aren't as important as with airplanes).

Let's say we're using a 3S cell and are playing only with prop size and motor kv. I can achieve the same thrust with different combos. What do I gain or give up?

e.g. I have an SK450 with 1000kv motors. AUW of just under 1kg using 3S 2200.
Initially set up on 8" props but anemic. Good on 9" and quite fast on 10".
Max power draw was 19, 28 and 40 amps respectively.

I also tried a 4s 2650 on the 8" props but it was a bit clunky - just wanted to try it out. I figure the 3S to 4S move is similar to changing from a 1000kv motor to a 1333kv motor in terms of the 'attempted rpm'. Ignoring the electrical efficiency for the moment, does anyone have a feel for the difference between small fast props and large slow ones on a quad? i.e. 1300kv with 8" vs 1000kv with 10". It's the flying characteristics I'm inquiring about. I'll move on to efficiency and flight time once I've wrapped my head around this part.
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