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I am assembling a drone. So far, I have learned that it is 450mm. I'm using 8 to 12 21700 Li-Ion batteries. When I search for AIO flight controllers, I believe I have to search for "30A" and "450mm" but I'm not sure. Is there an app or online service for winnowing down these decisions?

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    $\begingroup$ Try Bardwells fpvknowitall.com to get started 👍 $\endgroup$
    – Bor
    Nov 23, 2022 at 7:10

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You need a few things from a power system/flight controller. I don't think you should use an AIO, but that's personal opinion

Cell count

First things first - you say you're using "8 to 12" lithium cells. I imagine you won't be running these all in series, but it's necessary to point that out. Flight controllers and motor controllers have a maximum voltage they can support, 4S is common, 6S is also quite common, but slightly more expensive. 8S support is less common, and 12S support is in the X-class range and is prohibitively expensive for most people. I would start with either a 4S or 6S 21700 pack, and then consider adding a second one in parallel, but I digress.

Find a flight controller who's voltage rating is at least as high as how many cells you plan to use (it's okay if it's higher)

Motor control/AIO

The term AIO is well overused in this community to mean too many things. The way you've worded it, it seems you're looking for a flight controller with a built in ESC. That's acceptable, but you may have better luck finding suitable components if you use separate ESC and flight controller. You're including 30A in your search - this is good, but may be falling into a common misconception. You don't need a "30 amp" ESC, you need one that is rated for at least 30 amps (you could probably get away with 20). That means a 100A ESC is perfectly suitable for this application. Be careful not to limit your search by specifying a specific rating when you don't have to

Find an ESC (or AIO flight controller) that is rated for at least 25 amps and 6S if you plan on running a 6S battery

Frame size

You're building a 450 size quadcopter. That's a great place to get started - however the flight controller doesn't care. The frame you have will tell you (or you can measure) the mounting holes for a flight controller. It will likely be 45mm, 30mm (commonly 30.5), or 20mm. It may be any combination of these. This is the "stack size", or the spacing between the bolt holes for the flight controller to mount. You need a flight controller that is the same size as these holes - if your frame supports multiple then that opens up your options.

Find a flight controller with mounting holes that match with those in your frame

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In addition to the other answer, you need to consider whether you want a flight controller with features such as:

  • a barometer (for pressured based altitude hold)
  • a GPS input (racing drones don't use this, photography and survey drones do)
  • a convenient socket for DJI digital FPV
  • an SD card socket for recording black box information (for tuning)

Most other features will be common to all flight controllers, but these seem to be the main options.

Your other main choice is which generation of processor to use. There are still lots of really old FCs on the market (KK2, Naze32, CC3D) but they're nowhere near as good as a more modern board and it's not worth saving $10-20. There's a small but noticeable improvement in handling between F3 and F4 processors. Most people are now buying the latest F7 processors (I've no idea what happened to 5 and 6) The handling difference is barely noticeable but predicted to improve as the firmware is extended to use the extra processing power.

A 4-in-1 ESC that stacks neatly with the FC is nice for compact builds (i.e. race drones) but less important for larger drones. You may be better off with individual ESCs. That way they can be replaced individually if one fails. Note that ESCs get significantly more expensive when they're designed for more than 6s

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