6S Battery Limit – Why is it here and What to do with it?
The BFPVRA have pushed the Battery Cell cap to 6s in Drone Racing for the 2018 Season. In 2017 drone racers were limited to using 4s max batteries only and now in 2018, Drone Racers have an extra 7.4 Volts to play with BUT what should you do with it?
Nuggets of Battery Info
A LiPo Battery has a certain capacity which is measured in Milliampere Hour (Mah). You can compare this to the size of your car’s petrol tank. Capacity ranges hugely from 400mah to 12,000mah. You regular 4S capacity seen so commonly in the 2017 season was 1,500mah 4s packs. It gave enough juice for a 2 minute race whilst not having to run with a bigger battery. Again, a comparable to this is putting enough fuel into an F1 car for it to run to the end of the race so you can be as light as possible.
First of all, a little info on the batteries I will be talking about. A LiPo (Lithium Polymer) Battery primarily is rated by the number of cells they contain, from 1 cell (1s) to 10 cells (10s) and beyond. Each cell a LiPo has in it will hold 3.7 Volts. A two-cell battery (2s) is 7.4v, a three-cell battery (3s) will be rated as 11.1v. This is comparable to the size of a car engine and the effective BHP it can deliver.
Picture Courtesy of Brett Collis – Collision FPV
Ok, so now you know enough around batteries to understand a bit more of the rest of this article. The UK Drone Racing regulatory body, The BFPVRA, have pushed the Battery Cell Cap limit up to 6S for the 2018 season. This has caused a divide in opinion within the community, I’ve noticed the community having very valid conversations which normally end up in three distinct areas:-
- Recommended Spec’s
The community themselves have done a fantastic job of educating each other and discussing this on such a level that I feel everyone really understood. This is why I’ve taken the time to capture a lot of what was said into this article for future reference or to better educate drone racers.
This is where I’ll get just a little more techie. I read a lot of misinformed posts about the relationship of your Battery’s cell count and the kV of your brushless motor. So first, a little bit of education.
kV stands for rpm per Volt; so for every volt you are plugging into your rig, that is how many full rotations per minute the motor is rated at. This is why putting through more volts into your rig you are able to use a lower kV rated motor and gain the same performance.
So switching up to 6S and lowering the kV of your motor will give you the same flight characteristics of your 4S rig BUT it will also:-
LOWER your amp draw
MORE low-end torque
EXTENDED air time
LESS top throttle battery sag
SAME prop RPM and performance
This is the efficiency mindset I have been talking about and it really steps up your race strategy. You can keep high throttle for longer without sag, you’ll be ending a race with less amps drawn and arguably the MOST important point is this will help your prolong all of your kit. No more blowing ESC’s every weekend or stressing batteries to their limit. This helps you save the strain on the wallet.
This is not a mandatory change, Drone Racers can still race on their current 4S packs. A competitor can run any celled battery from 1s to 6s in the 2018 season.
Is 6s a pay to win option? I certainly don’t think so.
British Track Design will always be small, tight and technical, often running races of 10+ laps in a two minute race. For this reason alone, this is why speccing 6S with power in mind is a terrible idea in the British Drone Racing scene.
Skill plays a huge part in all of this, if you aren’t maxing out your 4S batteries at events, then the time isn’t right to be moving on up to 6S and you are better off to keep crushing it with your 4S setup.
Let’s not forget that 6s batteries are expensive, few and far between but the next level technology is slowly creeping in and I like the fact that the BFPVRA will be supporting manufacturers and early adopters alike to keep pushing the limits of British Drone Racers and the Drone Racing scene in general.
But how I hear you cry, it’s ok, it’s very simple. Just match your current 4s motor kV to a 6s KV with this handy table (provided by Mr Matthew Evans, Add1ct3dd) and you will see that you don’t lose any rpm on your prop.
You may have tested it before but there really is a sweet spot for prop rpm before the props THEMSELVES start flattening out and genuinely stop working.
I’ve found this to be around 50k rpm depending on the prop, so be aware you can over power your rig but this is for another day – Recommended RPM Sweet Zone between 37k & 46k.
Efficiency vs Brawn
If you wanted to negate all of my advice, which you are welcome to do but myself and a lot of the community would advise not to then PLEASE listen to these warnings as you may have multiple tech issues and it may hurt your bank balance considerably because:-
- You will pop the majority of ESC’s that are on the market due to the excessive amp draw.
- There will be lot of electrical noise to filter
- You will have to deal with huge amp spikes that can kill your rig
- Too much power to put down on a classic UK track
- Too many rpm’s will flatten props given unreliable performance
- You will still be flaming your batteries week after week
The above-overpowered setup as akin to a drag racer, on the very bleeding edge of its ability at all times and ready to blow, rather than an F1 car built for performance over a long duration of time. The dragster setup is not what you should want, look to to promote sustainability along with the BFPVRA. I recommend you DO NOT over kV and over prop your 6s setup but build for efficiency.
So that is really it for this post guys. Thanks for sticking with me through it. I’m going to leave this open for comments, if you feel like you have a different opinion or want clarification on anything I’ve stated in this article, let me know in the comments.
Obviously these are all my own views, as they always will be. My views are really directed at the British Drone Racing Scene, I know the US have now also lifted their cell cap limit but this article really concentrates on our little island.
I’m looking forward to how the 2018 stacks up.
Until Next Time – Adam Mackrory