In this post we will have a look at the difference of mini quad running 3S and 4S lipo batteries. Many who are building their first mini quad might struggle to decide which setup to go for, I hope this post can answer some of the questions. Also I will talk about how to move from a 3S mini quad setup to 4S, as I was asked a few times from FPV’ers who want more power and speed.
Let me know if there is anything else you would like to know, or mistakes.
Difference between a 3S and 4S Setup for Mini Quadcopter
It’s kind of obvious, the main difference is voltage that powers the motors. In my experience with cobra motors, the speed of my quad goes up a lot because of the extra 1S.
Let’s say we have a 2300KV motor, when powered under 3S lipo (12.6V), RPM (rotation per minute) is 2300 x 12.6 = 28900 (in theory). That means the motor spins 28,900 times a minute with no load. When you power the same motor with 4S lipo (16.4V), the RPM is 2300 x 16.4 = 37720, a huge increase in RPM.
Increase in RPM means more thrust, more power, and your quadcopter flies faster. However, the relationship of motor thrust and voltage is not linear due to efficiency loss. Some motors perform well in 3S, but not as good as expected in 4S where most energy just transforms into heat. Apart from thrust, we also need to consider other aspects such as torque, current draw etc. The easiest way to determine if your motor is suitable for 4S is to search for thrust data table, or test it yourself. Some motors rated for 3S simply cannot run on 4S, where the high voltage/current could damage and burn the wires.
Some might ask if a 3S quadcopter can out perform a 4S quad, the answer is definitely yes. Many factors come into play that can determine the speed of a quadcopter: combination of motors and propellers, weight, etc. But under the same condition, a multirotor that runs on higher cell count battery should have more power thus faster.
Also note that 4S setup are usually a little heavier than 3S, because of the additional weight of the voltage regulator, and heavier batteries.
I am new, should I skip 3S and go straight for 4S?
Yes you can just jump straight on 4S, I don’t see there is any problems. 3S builds are generally a little lighter. Might be a little easier to build as well since you don’t have to worry about voltage regulation, as most components supports 12V input (3S lipo) out of the box, for example video transmitter and FPV camera.
But if you are planning to use 4S in the future, get some 4S compatible components would be a good idea, such as ESCs.
Upgrading from 3S to 4S
Here are some tips in case you are getting bored of 3S, and want a faster mini quad. If you can afford it, you might also consider building another quad purely designed for 4S LiPo. It’s not a bad idea to have two quads when one is down for maintenance.
Motor and ESC
First question to ask is: can your motor and ESC handle 4S? For both increased voltage and current.
Popular 3S motors such as DYS 1806, EMAX 1806, T-Motor MN1806, Cobra 2204 2300KV and so on have been tested on 4S and seems okay. Of course you do it at your own risk, motors rated for 3S are not really designed for 4S, but it gives you the immediate results. It would be ideal to upgrade your motors to 22xx class with lower KV around 2000 whenever you can. (for example Cobra 2204 1960KV, or Cobra 2208 2000KV)
But be aware try not to run anything larger or higher pitch than 5030 on 4S with 1806 motors (which are usually rated for 2S-3S). When current gets too high, the little motor and thin motor windings will start to gather heat. If you keep pushing it, the enamel on the motor windings will burn off, causing electrical shorts inside the motor, between poles. Eventually it will lead to fatal power loss, and the motor will fail while your quad is travelling at top speed. And BANG! Your quad crashed into pieces.
Most 12A ESCs these days can run on 4S such as Afro, Blue Series ESC or KISS ESC, but it’s always worth checking first. When voltage increases, current draw will also go up. So make sure the motor and propeller combination you are planning to use would not exceed the current rating on your ESC. In some cases it’s necessary to upgrade your ESCs from 12A to 18A / 20A.
VTX / FPV camera / OSD
It’s very likely that either your video transmitter or FPV camera or both does not support 16V input. In which case a voltage regulator or a BEC is required to convert 16V to 12V (4S to 3S). I have been using this mini voltage regulator since I first built my 4S setup, it has never disappointed me.
Also make sure your OSD can read / be powered by 4S lipo. I made this mistake when I bought the Hobbyking E-OSD, and listened to some “rumour” that it can run on 4S although it’s rated for 3S. Spending $10 to watch some magic smoke is really not worth it. :) Since I have been using Super Simple OSD that takes 2S-4S, I like it because it’s plug and play, no configuration required.