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Can I use a 4S instead of 3S for this setup?

#1
Hi fellas, I recently scratch built my first plane and I also got the AXN floater jet and I am going to order some more Lipos for those 2 planes, but I don't quite fully understand which batteries I can and cannot use. My main question is if I can use a 4s for my scratch built plane or not. Here is my set up:

NTM 28-26 2700Kv motor
6x4 prop
HK 60A ESC
Zippy Compact 2200 mAh 3S 25C

I think this setup draws about 50A max. If I use a 4s, will it draw more or less amps? What size of battery and C rating would I need? Would I need a smaller prop? What would be in danger of overheating, the battery, ESC, or motor?

I understand that I asked a lot of questions here so much thanks to anyone one who can give me some answers!
 

earthsciteach

Moderator
Moderator
#2
According to the specs, both motor and esc are rated for 4 cell batteries. However, the 6x4 prop may be too much with a 4 cell. The 6x4 prop provides 520 W of power with a 3 cell battery. The motor data for a 4 cell battery is with a 4.75x4.75 prop and delivers 594 W of power.

However, the 6x4 on a 3 cell delivers more thrust (1.2 Kg) than the 4 cell with the 4.75x4.75 prop (1.12 Kg).

My question is, what sort of scratch build are you building that needs 520 - 594 W of power? :eek:
 
#3
Well, it doesn't NEED that much power. :) It is my custom creation with a 60in wingspan and 7in chord meant to carry my GoPro. My setup fits it well but it doesn't need quite so much power.
What would happen if used the 6x4 prop on it with a 4 cell? And why would the 4.75x4.75 prop have more W but less thrust??
 
#5
That engine seems a bit big to me. You might want to use a lower KV engine and swing the largest diameter prop you can for efficiencies sake.

Check out this thread. I'm sure almost every motor/prop/battery combo has been tried and evaluated at some point.

http://www.rcgroups.com/forums/showthread.php?t=972336
The reason for my high kv motor is because my plane is a pusher so I had to use a small prop. So I am going to order some different types of batteries to just play around with, but I don't want to endanger any part of my plane if a 4s is too big.
So would a 4s cause the motor to draw more or less amps?
And I'll check that thread out!
 

colorex

Rotor Riot!
Mentor
#6
So would a 4s cause the motor to draw more or less amps?
Depends... Power in Watts is Voltage in volts multiplied by Current in Amps.

So if the power stays the same, more voltage means less amps.

In brushless motors, more voltage means faster spinning - but then a smaller prop is needed to keep the power at the same level.

So higher cell count (higher voltage) and smaller prop means more speed less punch.

Higher voltage and the same prop will increase the amp draw! Possibly beyond the capacity of the motor!
 

robschonk

Senior Member
#7
Here's the data from the HK page for that motor:

Prop Test Data:
4.75x4.75 - 11.1V / 311W / 28A / 0.7kg thrust
4.75x4.75 - 14.8V / 594W /40A / 1.12kg thrust
5x5 - 11.1V / 400W / 36A / 0.85kg thrust
6x4 - 11.1V / 520W / 46.8A / 1.2kg thrust

The only instance where they go from a 3s to a 4s with the same prop, the current went from 28A/311w to 40A/594w.

You may need to experiment with different size/pitches and batteries, but USE A WATT METER, so you don't burn something up.

Headzuprc has some good information on prop battery combinations for the various motors they sell. Take some time to try to match the HK specs, and see what they recommend. Better yet, give the owner a call and see what he recommends for your application. He's supposed to be a good guy.

http://www.headsuprc.com/servlet/StoreFront

They also sell a motor mount that will allow you to use a different motor, or to mount it higher to swing a larger prop.

http://www.headsuprc.com/servlet/the-MOTOR-MOUNTS-cln-Easy-Star-I-Adjustable-Mount/Categories
 
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#8
Ok, thanks for all the answers guys! I think I am going to hold of on a 4S battery right now, at least for this set up. I don't have a watt meter so I'd probably end up breaking something!
 

robschonk

Senior Member
#9
Ok, thanks for all the answers guys! I think I am going to hold of on a 4S battery right now, at least for this set up. I don't have a watt meter so I'd probably end up breaking something!
Every one needs one in their toolbox. Otherwise, you're just guessing, and you may burn something up.

Not expensive. Also has a volt meter and battery balancer. Here's a link to one from HK, but I bought mine off eBay for less than $20ppd, and had it in 10 days.

http://www.hobbyking.com/hobbyking/store/__10786__HobbyKing_HK_010_Wattmeter_Voltage_Analyzer_.html
 
#10