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PostPosted: Tue Jan 04, 2011 5:45 pm 
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Joined: Sat Mar 29, 2008 5:28 pm
Posts: 389
k...
I wont need a lot or power since it is a glder like UAV

also...

I dont know if I could fit a 4s 4000 in it...
Possibly a 3s4000 maybe.

It is still in the box. I move into my new living quarters tomorrow finally at my new AFB.

Also, its going to be a different flying zone here do to the constant 10-20 mph wind AlWAYS!!!!!

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PostPosted: Tue Jan 04, 2011 7:53 pm 
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Joined: Tue Jan 15, 2008 8:50 pm
Posts: 186
Britt,

You really need a 4s battery. If you go to a 3s it's going to hose a bunch of stuff. Here is why:

If you take a 3s battery and say you get 3.5v under load. That means your going to get around 10.5v out of the pack while your running it. If you take the KV of that motor and multiply it by the voltage you get 7455 rpm (10.5 v x 710kv) . That is just too low. Keep in mind that is without load so the motor will try for that, but I doubt it will reach 7000 rpm. If you take another 3.5v for the 4th cell then you get 9940rpm which is much better.

Another problem is the amps. In order to make 900 watts on 10.5v you need 85 amps ( 900 / 10.5 = 85.7) so your going to be working your batteries really hard.

One thing you could do is go to a 2200 5s pack. That would give you more rpms (12.5k rpm) and less amps (51a) but you would need to run a smaller prop on it.

Basically a 700-800kv motor on 4s and a big prop is like a .70 four stroke and the same motor on 5s and a small prop is like a .46 2-stroke.

If you did that you could buy a turnigy 60 amp esc if you want to go that route. As far as run times, a 5s2200 battery has 40.7 watt/hours (18.5v x 2.2a) and a 4s3300 battery is around 49 watt/hours.

schu


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