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Old Aug 10, 2012, 01:52 PM
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Habu 2 or eflite Yak 54 on a 3s batt?

Hi guys,

Does anyone know if it possible to run either one of these a/c on a 3s batt vice a 4s. I am doing a cost breakdown and the idea of picking up a new plane and then having to pick up some new batteries given that all mine are 3S does not sound appealing.

I know that there would be a big performance hit on the yak and likely some on the habu (although it is still a 15 engine).

Or is this just going to be one of those times when I have to shell out a bit more coin than I had intended.

Thanks!
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Old Aug 10, 2012, 03:29 PM
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United States, VA, Ashburn
Joined Apr 2012
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There would be a huge power drop on both. Even more so on the habu.
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Old Aug 10, 2012, 03:38 PM
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eye4wings's Avatar
Ware, herts. U.K.
Joined Sep 2008
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Theoretically I see no reason why a 3S pack should not fly those planes. Most of my models are designed for 3S and I agree it is nice to standardise for interchangeability.

What you would need to do though is first change the prop for one with greater diameter and pitch, which means that your current draw will go up. The next question is whether the motor and ESC can cope with the extra current (assuming you are buying both with the plane). If not then you are looking at the cost of a new motor and ESC versus a 4S pack. My guess is that the likely cost would be about the same so the easy way is to buy a new pack.

On the other hand if you are buying a model without motor and ESC and have to provide them too then it will be wise to take the opportunity to get yourself equipped with a watt meter. One of these is essential equipment for anyone making alterations to stock configurations and will save you wasting money through burned out components.
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Old Aug 11, 2012, 12:04 AM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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Nope.

The battery voltage will directly affect the RPMs the motor spins at, which will directly affect the current draw for a given prop size, which directly affects the system's total power (both into the motor and out to the prop/rotor).

- For the Yak, the prop size could be increased until the motor is drawing the same amount of current as it would with the stock prop, but your maximum total power (V x I) will be less due to the decreased voltage. You'd probably be able to get it to fly, but it just wouldn't fly as well as it would with a 4S pack the way it was designed.

- For the Habu, you can't just increase the prop size since it's an EDF. This means that you'd simply have a very big reduction in power with no way to gain it back.

You COULD fly them with stock performance on 3S, though. You could find motors that are the same size and weight as the stock motors, but with Kvs that are 33% higher. You'd also need to replace the ESCs with bigger ones to handle the increased current.... But it would be cheaper just to buy 4S packs
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