What's The Smallest FPV Drone 6s Batteries Make Sense On? Should I Put 6s On 2.5"? - FPV Questions 

Fun fact, magnets losing their effectiveness under heat is how those cheap $10 rice cookers work. Once all the water is gone, the heat radiates down into a magnet until the magnet under the bowl "fails". The switch flips from cook to warm.

Great answer. Very interesting. I just built a 3.5" freestyle quad, went with 4s, but wondered about 6s when I was picking motors.

Bardwell has explained it theoretically, assuming you have the batteries. In practice, however, it ultimately depends on the availability of the batteries (unless you make them yourself). And the simple fact is that the smallest 6S battery is 1050 mAh (for me my main market). And that limits how small the drone can be for that battery. And in my opinion, in practice, 6S only makes sense with a 5 inch medium weight. At 5 inches ultralight and under 5 inches 6S makes no sense in my opinion (except for 3-4 inch cinewhoops maybe).

Theres a couple of points I disagree with here, but they are pretty minimal. The first one is there are functional limitations on how you can wind a motor that mean there's a limited Kv range you can achieve with a given stator size and magnet combination. In a lot of cases that is the functional reason you end up changing voltages as motor sizes increase even before you run into the power delivery limits of the batteries. Now our 5" drones sit in an interesting space where we can achieve a decent range of Kv pretty effectively, so that's not really a limiting factor for a lot of what were doing, but for instance you can't functionally make a 0702 motor low enough Kv to be useful on higher voltages due to not being able to fit enough turns on the windings with sufficient gauge wire. Same is true in the opposite direction on larger motkrs. At sone point you are at only one or two turns per armature on the stator to achieve the Kv you want. I also would point out there are a lot of other factors like switching losses and relationship between duty cycle and efficiency of the motor that matter a lot in where optimum voltage and Kv will sit for a given application. Moving the throttle point that is the most used into a more effective band for the motor is a key part of the discussion, and often that is achieved by lower voltages, not higher. It depends on the specific application of course. My main point woild be that the real point at which you want to go up in voltage is when you exceed the power delivery requirements of the lower voltage in terms of how many watt hours of battery you can carry and how high you can push the Kv. To that end, I don't actually think 6S makes sense until you get above 2000kv or so. If you actually look at the details of the setup, most folks are running 6S 1300mAh batteries. Those are roughly watt-hour equivalent to 4S 2000mAh, and a 4S battery of that size can pretty easily handle the load of motors up to 2800-2900kv without running into limitations. That's Kv equivalent to 1950kv on 6S at the top end, so unless you're pushing past that point you're just sacrificing efficiency and stressing the voltage ratings on the regulators on the low voltage electronics by moving to 6S without gaining much if anything in terms of power delivery. 90% of the supposed gains people see in going to 6S is because they're simultaneously going to a higher relative capacity battery that has a higher output relative to the voltage. The other factor is that due to demand everything currently has been optimized for 6S. Compare the number for 4S 2000mAh batteries to the number of 6S 1300mAh batteries available at the FPV shops for example. Also look around for ~2800kv motors snd compare it to the selection of ~1950kv 6S motors. Anyway it's a fun discussion, but in the end it's more academic than practical. Anything in close to the right range will work great and fly well, so in the end flying whatever works for you and is readily available is the right choice regardless of the technicalities of why or minor optimizations. Fly what you enjoy and have access to! It's just a lot of the commonly shared info on the topic is inaccurate at best.

I fly a 3" on 6s with tmotors 1507 2700kv and it fly absolutely great and much power it gives👌🏻

We use outrunner motors for the torque. People who were there in the beginning should know this. 😉

I just like using the right motor for the right rating , its less complication, and better flying time, I did put 6s on a 4s quad, it flew ok, but didnt like the difference, it was screaming too much. I have 1 4s quad and its already a beast on 4s, nazgul evoque , aint going nowhere, its my go too quad.

I have s quadmula Djinn 2.5 inch with 3000kv on 650mah 6S and flys great

I've built 2.5 inch 6s cinewhoop and my reason was longer flight time. But I wouldn't recommend going below 2.5 inch, hell I recommend don't go lower 3 inch if you truly want to be efficient.

The real benefit to higher voltage is LESS AMPS for the same amount of work done. Thats why your heavy amp draw household appliances aren’t 110v. Because they draw half as many amps at 220V for the same amount of work done at 110V and your electric meter is charging you for the amp usage. In the context of mini quads, less amps, means you need less wire gauge and battery connector size for the same amount of work or less voltage drop over the same wire size. So from an efficiency standpoint and a weight saving standpoint, you should see better and better results as overall mini quad weight goes down… to a point of course

Not arguing but try the quadmula djinn on 6s. You can really dominate your movement against the air.

Awesome

but what about difference in voltage sag between cell counts?

Up to 1804 size motors you can stay with an 850mah 4s and xt30. Woth more power hungry 2004 and bigger motors you will want 650 to 850 mah 6s xt30 lipos. Just my experience from building many many 3 to 4 inch quads. You can push an xt30 up to 90A burst. No problem. It's only for a few seconds. Beyond that either change to xt60 and bigger 1200mah 4s lipo or stay xt30 and use 6S 850mah lipos.

So i fly 6s on a 21 inch prop and rarely get more than 22 min flight times... its a big ass 36,000 MaH 6s tattu and 320Kv t-motor... what can i do to get better efficientcy (the quad weighs 18.5 pounds)

6s on 3 inch every time for me. Ballistic.

Yes AND… lol. You can get away with XT30 and smaller wire much easier on 6S. So if you want to try to get an HD 3 or 4” quad under 250g, you may NEED those few grams of weight savings

I'd say this... 3", 3S. 3.5", 4S... Bigger, higher.

Quadmula f25 build help! DJI o3 air unit Elrs Should I go 6s or 4s? I see a lot on 4s and a lot on 6s. Can't decide. Some people ive asked say def get 6s Should I get the speedybee f405 V3 mini stack to save money or is it worth spending more for the mini t motor f7 stack? Any other recommendations? Thanks for any feedback or suggestions!

Lower KV almost always equals more torque...in practice. I will demonstrate: 1. Same voltage eg 2400kv vs 2700kv - Your power limit is the amps the battery can dish out, the lower kv motor produces more torque for the same amount of current, therefore more torque. 2. With different voltages eg 4s vs 6s - manufacturing benefits, also heat build-up effects efficiency, system is power limited so better efficiency = more torque, ALSO the rest of the system doesn't change (typically) the motor resistance might drop proportionally but you don't use different escs, wiring or connectors which also produce losses, therefore lower current = more torque. TL;DR, system power limitations, motor manufacturing, heat buildup etc all mean that for all practical purposes lower kv = more torque.

Holy smokes 6s on 30mn prop? Sheww

22 min fly time with 21 inch props on 6S? None of that sounds right. First off I’ve never seen 21 inch props. And 22 minutes on a lipo? Never. You sure you didn’t type that wrong?