4S LiPo is currently the standard battery cell count for FPV mini quads and racing drones. As we are all continuously striving for more performance in our quadcopters, 6S setups might be a better option, or not?
There are different opinions on what benefits 6S can give us over 4S. Note that we are still at the early stages of experimenting with 6S batteries on mini quads, a lot more testing is needed to verify these theories.
Further Reading: New to FPV Mini Quad? Take a look at our beginner’s guide.
Benefits of 6S Over 4S
A 6S LiPo battery has higher voltage than a 4S because of the two extra cells connected in series. This results in a higher maximum voltage of up to 25.2V in a 6S battery, compared to 16.8V of a 4S.
Potential improvements of running 6S compared to 4S are:
- LOWER amp draw
- LESS voltage sag
- LONGER flight time
- MORE responsive and agile performance
Lower Amp Draw
One of the most important advantages of 6S over 4S is the lower current required to produce the same power.
As we know, power is calculated by multiplying voltage and current, P = V x I.
To achieve the same amount of power, a higher voltage will reduce current draw. 6S is 25.2V when fully charged while 4S is 16.8V. For example, to produce 1000W, it takes nearly 60A on 4S while it’s only under 40A on 6S.
Lower amp draw translates into:
- Less stress placed on your battery
- Less “voltage sag” for the duration of the flight
Let me show some DVR of a flight on 6S.
Better For Your Battery
The lower amp draw will keep the battery at a cooler temperature during flight, which is beneficial for the health and longevity of your batteries. You could even use lower C rating packs and achieve the same power, therefore you might be able to select less expensive batteries.
However, to match the weight of a 4S battery we do tend to choose lower capacity batteries, which can limit your maximum discharge current… So you might still want to use higher C rating packs.
Max Discharge Current = C Rating x Battery Capacity
From my experience I have found a 6S mini quad to be highly responsive and has a great amount of control through the entire throttle range. It has the ability to accelerate almost instantly yet it doesn’t feel as “floaty” as I expected it to be.
The advantage of that agility and acceleration come from the higher voltage, and the lower voltage sag under load. These enable the motors to change RPM more rapidly and effectively, resulting in a more responsive and agile craft. The faster rate of RPM change is probably one of the most significant factors when it comes to the handling of your quad.
One theory suggests that a 6S quad gives longer flight time than a 4S.
This is not necessarily true since we try to select 6S batteries of the same weight, or Watt hours (Wh) as 4S batteries for a racing drone. To achieve similar speed on a 6S, the motors have to be spinning at similar RPM and therefore it will require a similar amount of power. So in theory, flight time should be similar to a 4S as well if we aim to fly at the same speed.
You can have longer flight time on a 6S by either reducing the power of your motors (e.g. lighter props, or less aggressive flying), or using a larger battery pack that can store higher energy. But either way will inevitably impact the performance of your aircraft.
I think the benefit with flight time can only relate to an AP platform (aerial photography) where motor speed is more consistent and you are not spinning motors up and down so rapidly like a racing drone.
6S is Faster??
Without a doubt a 6S quadcopter with specially selected components can outperform a 4S (that’s why one of the fastest drone world records is set by a drone using 10S battery and not 4S). But in my opinion, 6S is not necessarily faster if you intend to build it having the same or better efficiency than your 4S quad, where the props are spinning at the same RPM.
When it comes to drone racing, race tracks are often setup with lots of turns and gates which require just as much pilot skills as raw speed, if not more.
But lower current draw and voltage drop give the racer more headroom to experiment with motor and prop combinations. This flexibility allows more strategies by finding the best balance between efficiency and performance based on the specific race track.
Building a 6S Mini Quad is More Expensive
Not only our options for 6S compatible components are currently limited, they are also priced higher than parts designed only for 4S.
In order to support higher voltages, all supporting electronics need to be specially chosen in order to handle the higher voltage spikes, such as the capacitors, MOSFET’s, voltage regulators. 4S parts are cheaper because they are making them in a larger volume.
Choosing 6S LiPo Batteries
The idea here is to pick a 6S battery of similar “watt hours” to what we normally use on a 4S quad. “Watt hour” (Wh) is a measure of how much energy is stored in the battery, which is calculated by:
Wh = Capacity x Voltage
For example a 6S 1000mAh should give you similar flight time to a 4S 1500mAh. Of course the weight should also be considered when choosing a battery.
This is not the most accurate calculation because we are assuming our 6S setup has the same efficiency and power to our 4S setup, but it’s good enough to get us started.
|4S (16.8V)||5S (21.0V)||6S (25.2V)||Wh (mAh*V/1000)|
|2100 mAh||1680 mAh||1400 mAh||35.28|
|1800 mAh||1440 mAh||1200 mAh||30.24|
|1500 mAh||1200 mAh||1000 mAh||25.2|
|1300 mAh||1040 mAh||867 mAh||21.84|
|1000 mAh||800 mAh||667 mAh||16.8|
6S batteries are generally more expensive than 4S, and there are currently very few options, here are the ones I’ve tested so far:
- Amax 6S 75C 1150mAh
- Tattu 6S 95C 1300mAh
- Genace 6S 45C 1050mAh
Further Reading: How to choose LiPo Batteries for Drones?
Choosing Motors for 6S
There are two sides of the argument when it comes to selecting motors for a 6S racing drone. Some recommend to run lower KV motors and match the theoretical max RPM of 4S-equivalent motors. Others suggest we can use motors of similar KV to what we use on 4S and take full advantage the extra power from 6S batteries.
I will experiment with both ideas in my testing :)
Lower KV Motors
For a safer and more efficient setup, you can find a very low KV motor that gives you a theoretical max RPM in the same range as an equivalent 4S setup using a common KV rated motor (e.g. 2500KV).
|4S – KV||5S – KV||6S – KV||RPM (VxKV)|
Because you are using more volts in the system, you do have the ability to execute the KV more effectively. So in fact you actually need even slightly lower KV than you would calculate to achieve the same RPM in flight. That means we might be looking at 1600KV on 6S = 2500KV on 4S.
As you move up in KV on the motor, it’s said the torque rating goes down, but from my observation the more influential factor is voltage sag that prevents you from actually reaching the theoretical max RPM on 4S.
With the 6S setup I am also noticing the ability to swing a heavier prop (e.g. higher pitch) more effectively. If I were using a 4S LiPo, most high KV motors just don’t have the grunt to swing a heavy prop at the high RPM I see on the 6S setup.
Higher KV Motors
I have been suggested to try some higher KV motors with 6S and I was told the result is remarkable, such as 2000KV or even 2300KV motors, which is equivalent of 3000KV-3500KV on 4S.
These “high” KV motors on 6S should give brutal straight line speed and grunt in the corners. The downsides are obvious: terrible voltage sag and you lose any of the efficiency gain from running lower KV motors.
In order to avoid drawing too much current and maintain better efficiency, you can try to limit your throttle, for example using throttle curve in your radio, or set maximum throttle in Betaflight.
Update (April 2018) – I tested high KV motors on 6S and here is my finding.
- Amax 2305 2350KV (Review (coming soon) | Buy: Amaxshop)
My 6S Build
Feb 2018 – Amaxinno 5″ Build Log
- Returner R3 2206 1720KV Motors
- Aikon AK32 35A 4in1 ESC
- Matek CTR F4 AIO FC
- Runcam Micro Eagle FPV Camera
- Eachine VTX03
- Frsky R-XSR Receiver
- 1000uF Low ESR Capacitor
How about 5S?
Well the cell count and voltage of 5S are in between 4S and 6S, so you can expect the performance is also in between the two. But there are more components supporting 5S due to it’s lower voltage. I only tested 6S because it’s more “extreme”. :)
I am still testing as we speak so this is not the conclusion yet.
But so far I really like the performance of 6S! Slightly longer flight time for freestyle flying, and the quad’s response feels so such sharper and direct! I really think it has the potential to replace 4S if there are more component options, and prices drop to the same level as 4S.
Oh, how many people still remember the discussion back in 2014/2015 when we were still deciding between 3S and 4S? :)