Benefits of 3s vs 4s, if any…

[Rod]

Hi & thank you for all the efforts to make this awesome hobby/experience available for everyone to learn!
So my question is… Advantages/disadvantages to building a 3s vs a 4s setup, and also if there’s the possibility of using a Graupner 3-blade Eprop (left) 9×5 instead and if so would I have to change motors to something much more specific?

Thanks for any input and keep on flying!

[ashbreeze]

The only difference is that a 4s will give you more power to just shoot straight up out of bad situations, which is very handy when flying FPV.

A 3s will let you run 12V based electrons straight off of the pack, but most modern extra components (Immersion 5.8G TX, etc) should run just fine on a 4s. Make sure to check the specs though.

Other than that there aren’t really any upsides / downsides.

If you aren’t flying FPV and you don’t plan on it, you could go with 3s and save a little bit of money.

But if you are flying FPV or might in the future, a 4s is basically a must have.

If you use 3 bladed props you will have to downsize them to compensate for the extra blade and use a different motor, and possibly a different ESC. (I don’t have any experience with 3 bladed prop / motor setups so I can’t give any recommendations) The less blades you have (unless you only have 1), the more efficient the prop will run.

[Terje]

Well, there is the benefit of getting more watts out of your setup. The Afro 20A slim ESC (2S-4S) and 18AWG wire are rated for 20A. Amps is what melts your wires and ESCs. Watts is what makes your motors powerful generally speaking.

For each motor:
A 3S setup will have a theoretical watt limit of 12v x 20A = 240 watts
A 4S setup will have a theoretical watt limit of 15v x 20A = 300 watts

Also the LiPos “contain” more watts per mAh in a 4S lipo vs a 3S lipo:

Lets compare 2200mAh 40C lipos…

2200mAh 3S 40C lipo: 2200mAh x 12v = 264 watts – continuous draw: 88A
2200mAh 4S 40C lipo: 2200mAh x 15v = 330 watts – continuous draw: 88A

4S tends to be a bit heavier than 3S with the same mAh and C rating though. What makes most sense is to compare the watt to weight ratio.

[RCExplorer – David]

Like Terje said,
Higher voltage is more efficient as you can run lower currents to get the same work done (watts). It’s the current that introduces waste heat into the system (the current squared times the formula for waste heat)

Higher voltage also energizes the poles in the motor a bit faster and provides a little more torque.

The biggest advantage is that you can use lighter motors, speedcontrollers and wires as you’re drawing less current. Which gives with higher efficiency gives you longer flight-times.

That’s the theory, the difference between 3 and 4s in this application, and depending on how you fly might be less.

If you’re going to use 3 bladed props you need to use lower kV motors,
I suggest using the http://www.ecalc.ch/xcoptercalc.php?ecalc&lang=en to calculate what you need 🙂 Works great

[Author]

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