Since we don't include a battery with our RTB 250 Class Quad Kit we have decided to do a little bit of testing so you can make an informed decision about which one to buy. Also, it's nice to get a rough idea about how long your quad will stay in the air. Although we made every effort to make this a fair test, variances will always play a part in the results; we have tried to make note of any environmental factors which may have affected with the data.
It's worth noting from the outset that this test is intended to show the relationship between battery capacity, weight and flight time in LiPo batteries and not specific times for specific batteries. Although you might not use these exact batteries in your build, the relationship between capacity, weight and flight time should remain relevant across most LiPos battery models.
The RTB 250 Class Quad Kit is made up of the following components:
- Diatone G10 FPV250 frame
- 4x eMax 1806 2280KV motors
- 4x AfroESC Ultra Light 12A ESCs
- Naze32 Flight Control Board
- Gemfan 5030 propellors
- Power Distribution Board
Also on board was the FrSky Battery Voltage Sensor and the FrSky D4R-II receiver. The total weight without battery was 308g.
Although the ESCs and the Power Distribution Board in this kit can handle 4s batteries, the motors are only rated for 2-3s batteries and so this is all we have included in our testing. Using a 4s battery with this kit is not advisable.
These are the batteries we used for testing:
- Turinigy A-SPEC 65C 2200mAh (196g)
- Turnigy A-SPEC 65C 1800mAh (160g)
- Turnigy nano-tech 35-70C 1500mAh (130g)
- Turnigy nano-tech 45-90C 1300mAh (120g)
As you can see, we have used different cell chemistries in the testing. This was mainly due to stocking issues and while there is an argument that this might make a difference, when all is said and done it probably doesn't. All of the batteries used are a premium grade of battery and have a higher discharge rate than some others which are available (eg, Zippy Compact, etc.). Due to thicker metal plates in the cells, they are also slightly heavier than those batteries with a lower discharge rate (eg. the Turnigy A-SPEC 65C 2200mAh weighs 196g while the Turnigy 2200mAh 25C 2200mAh weighs 194g).
Two tests were performed with each battery:
- Hovering (indoor flight manually kept in the same position)
- 'Real world' flying (outdoor flight, gently following a consistent circular route at medium speed)
We used the FrSky Battery Voltage Sensor in conjunction with the FrSky D4R-II Receiver and the FrSky Taranis X9D Transmitter to monitor the battery voltage. Each test was started with a new battery after a full charge and the battery was deemed discharged when the reported voltage dropped below 10.8V. The quad would still fly after this point but discharging the batteries any further would risk causing permanent damage to the cells and you shouldn't really be doing this on a regular basis anyway. After each flight, the battery voltages all rose back up to roughly 11.2V.
Hovering vs 'Real World' Flying Results:
From a purely anecdotal perspective, while the results obviously trended towards a longer flight time with a higher capacity battery, this does not paint the whole picture. The response and handling was very different across the range of batteries. For example, with the 2200mAh battery and to some extent the 1800mAh battery, the quad 'felt heavier' in the air. The controls were dampened almost akin to having a lower RC rate setting and this became increasingly noticeable as the battery discharged. On a positive note though, if you wanted to use the quad for aerial videography the dampened flight characteristics might help with recording smoother footage.
At the opposite end of the spectrum, with the 1300mAh and 1500mAh batteries the quadrocopter felt more sprightly and responsive. There was almost no 'pendulum effect' and it felt as though it was 'on rails'. If you wanted to use this quad for acrobatic flight or racing then these would be the batteries to go for.
While the difference in handling across the batteries was noticeable, it is worth saying that the quad actually flew very well with all the batteries we tested - you certainly wouldn't be disappointed with any of them on this quad.
Potential Factors Affecting Test Results:
Human Input - Since both of the tests were performed under manual control, it is conceivable that inconsistencies in operation could have led to inaccuracies in the results. That being said however, the tests were all performed by the same person in a reasonably short space of time so I think we can say that any effect this factor may have had is minimal.
Wind - The outdoor 'real world' flight tests were obviously performed in the open air and the wind was a factor over which we had no control. Average windspeed at the time of testing in the area was around 5m/s but changeable. In order to stabilise the quad, the flight controller has to tell the ESCs to send power more erratically to the motors which will obviously affect the draw on the battery. Unfortunately, we have no way of telling how much of an effect the wind had on the tests.
Battery Chemistries - This has already been mentioned and not ruled out as an impacting factor. According to documentation the A-SPEC batteries have an additive which causes lower internal resistance. This leads to less heat generated and less voltage sag under load. The way the batteries are constructed also makes them slightly lighter than their nano-spec equivalents. Both of these elements could translate to increased performance aside from the capacity differences.
Although we cannot rule out any of these factors as significant, after looking at the results they still conform to both third party tests and our own expectations. It's fair to say that we think the test results are reasonably accurate, and even if they are not a completely fair test of the differences in capacity, they are still useful when deciding which battery to buy for this particular build.
Here is a price list of the batteries (at the time of testing) and links to where to find them:
Turinigy A-SPEC 3S 65C 2200mAh (£19.83)
Turnigy A-SPEC 3S 65C 1800mAh (£18.73)
Turnigy nano-tech 3S 35-70C 1500mAh (£10.48)
Turnigy nano-tech 3S 45-90C 1300mAh (£9.15)
The above links are for batteries listed on the Hobbyking website. Stocking issues in their UK Warehouse however are almost becoming notorius so if the battery you want is in stock then buy it while you can!
As previously mentioned, our testing was purely based on flight times vs. capacity/weight and was not intended to test different battery types. As you can see however, the difference in price between the nano-tech and A-SPEC batteries is quite considerable. The 1800mAh A-SPEC is almost twice as expensive as the 1500mAh nano-tech. In our testing the flight time vs. capacity relationship was quite linear whereas the price between the two battery types is certainly not.
The A-SPEC batteries are purported to be of a higher build quality and may well last longer but in my personal opinion, when compared to another battery with a similar C Rating, it remains to be proven whether the gains are actually worth the additional cost. Obviously this is a personal view and whether you will buy them or not is down to your own opinions.
As I have already mentioned, the A-SPEC and nano-tech are certainly not the only batteries you could use; we used these batteries for their consistency across the test flights. There are other battery models which are perfectly capable and less expensive. The Turnigy 2200mAh 3S 60C LiPo Pack for example can handle the necessary current draw and is currently only £12.93 as compared to the equivalent capacity A-SPEC model which is £19.83. This difference starts to add up when you start buying multiple batteries.
We happened to have one of these cheaper batteries in the office and just out of interest, decided to give it the same hover test as we gave the other batteries. Here is its time as compared to the more expensive A-SPEC equivelant:
As you can see, the difference is not huge and the cheaper battery was not new like the more expensive ones were.
Choosing Your Own:
When it comes to choosing your own LiPo batteries for your multirotor build, aside from the capacity (measured in mAh) and the voltage (3.7V multiplied by the number of individual cells in series in the battery - 2S, 3S, 4S, etc.) you also need to make sure the battery can handle the current draw from your motors and ESCs otherwise it will get too hot and possibly cause permanent damage.
If we want to work out the nominal constant current draw from these components we have to add together the ESCs' current rating. In this case we have 4 x 12A ESCs so a reasonable estimate for the maximum constant current draw is 48A.
To find a battery's maximum constant discharge rate, multiply its capacity (in Amps) by its C rating (always use the lower number - the higher number indicates the maximum 'burst' output rather than the 'constant' output). The result is measured in Amps.
Let's use this calculation to test a couple of batteries. Firstly, the Turnigy A-SPEC 3S 65C 2200mAh (which we used in our testing):
As you can see, the maximum discharge rate of the battery is 143A which is well over the 48A maximum constant draw of the battery. This battery is fine to use. Now let's work out how whether the Zippy Compact 3S 25C 1300mAh battery is a suitable choice:
The 32.5A maximum discharge rate of the battery is lower than the maximum draw from the ESCs so this battery is very likely unsuitable for this quad. I should mention that the combination of motors and props also affects the maximum draw from the quad but you should be fine just using the ESCs constant current rating for your calculations. Add on a little margin and you can't go too far wrong.
At the end of the day, which type of battery you buy will come down to your own personal preference based on price, capacity, build quality and availability. Just make sure that you pick a 3S battery with a capacity roughly between 1300mAh and 2200mAh and a C rating which allows a sufficient discharge rate for your build.
If you want to fly for a long time regardless of how this quad flies, get a 2200mAh battery. If you want to race the quad or otherwise fly it acrobatically, get a 1300mAh battery. Always, always make sure the C Rating of your battery is high enough to handle the current draw of the ESCs and motors though. Remember, the HobbyRC RTB 250 Class Kit has a nominal maximum current draw of around 48A.
Better still, get one of each. You'll probably end up buying more than one anyway since 11-12 minutes of flight time doesn't make for a day out! If you plan to upgrade this build for FPV flight, don't forget that you'll be adding more weight anyway and perhaps a lighter battery would be preferable in this situation.