2 cell or 3 cell for twin? - RC Groups
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Oct 17, 2005, 02:35 PM
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2 cell or 3 cell for twin?

I've been debating for some time now and can't make a good conclusion so I thought I'd see what others think.

I'm building a twin engine plane (Cessna 310) and I can't decide on what power system or battery setup to go with. I'm focusing on minimizing cost but keeping effieciency high. The plane is set to be about 8oz with everything but motors, esc, and battery, so I'm estimating 16-18oz total flying weight.

I can't decide if I should go with a 2 cell or 3 cell setup. I'm mostly looking at getting 2 BP21's that have a KV of 1700 and 13oz of thrust at 7.2V and 8.6A on an 8x4 prop. Two motors would mean 26 oz of thrust total on a 2 cell, which is more than enough I would think.

The huge question I can't decide on is if I should stick with 3 cells though and run a smaller prop. I simply don't know if it's better to go with a 3 cell and down size the prop, or go with 2 cell and pull more amps?

It looks like a 2S 2100 weighs about the same as a 3S 1300 pack, and they both have close to the same volt amps storage, and they cost about the same.

Does a 2S(more amps less volts) produce more or less heat/less effienciency than a 3s(more volts less amps)?

For scale reasons I need to run either an 7 or 8 inch prop.

I'm also somewhat stuck on BP motors because of the price. I'm already on track to be over budget. I may switch to using BP12's if I should go with 3 cell, since it's 200kv less (1500kv), or maybe the BP8Y (1260). If someone knows of smaller motors that will put out 10-15oz of thrust and are sub $30 motors, I'd be open to that.

Last edited by morphideous; Oct 17, 2005 at 02:45 PM.
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Oct 17, 2005, 05:57 PM
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vintage1's Avatar
Oh...how about a pair of IPS 'A' units and 7x6 props and 3sLIPO.

Cheap....at half the price...

should be 10 oz of thrust and 30mph pitch speed - more than enough for a lightweight twin..under 4A total draw so a 450 pack is useable.

What cell count you pick is just to suit the motors.
Oct 17, 2005, 06:41 PM
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Those IPS's look like they're not 10oz of thrust each, more like 6oz, which isn't enough, I need 20-30oz of thrust for this plan total. Interesting idea though. I did some checking on brushed motors, but they're not that lite, 2.33oz for an IPS-A is a lot of weight... Compared to 1.5oz or less for brushless.
Oct 18, 2005, 03:56 AM
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vintage1's Avatar
apologies: Thought you wanted 10oz total...

I question the need for twice as much thrust as the plane weighs...?

Cessnas are not known for prop hanging

IPS motor is a shade over 1/2 oz..

A pair of them on my scales with boxes shafts and extra suppression caps comes to 2oz dead.,A 3sLIPO 450 pack for hem is 1.5oz. Total weight of motors and pack and ESC about 4oz all in.

I can assure you that a pair of these will fly a model like that with adequate authority for decent scale flight.
Last edited by vintage1; Oct 18, 2005 at 04:01 AM.
Oct 18, 2005, 10:12 AM
Registered User
4oz isn't bad... The Cessna 310q does have quite a bit of power, it's one of the only planes that came take off on a single engine. I agree 40oz is overkill, which is why I am debating having the 2cell, which would give about 26oz of total thrust. Which IPS system are you talking about? Brushless, or the GWS ones?

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