so ive been lurking here for like 6 months watching builds and finally pulled the trigger on putting together a 5inch freestyle quad. went with a dead cat style frame i got off aliexpress, hyperlite flowride motors (2207 1900kv), and a 45amp 4in1 ESC stack i grabbed used off someone local. everything seemed fine when i bench tested it at low throttle but the second i really punch it the ESC starts smelling and once actually had a tiny wisp of smoke come off one of the corners.

i checked my solder joints and they look ok to me but im not super experienced with a iron so who knows. battery is a 4s 1500mah tattu. im wondering if maybe the used ESC is just toast or if i did something wrong. also not 100% sure i have the motor order right in betaflight, could that cause this? i havent maiden it yet obviously

wrong motor order wont cause smoke, itll just make the thing flip on the ground and maybe crack a prop. the smoke is almost definitely the ESC and if you bought it used theres a real chance one of the FETs was already marginal and your soldering heat finished it off or the previous owner burned it and didnt tell you. 45amp should be more than enough for 1900kv on 4s but a damaged ESC will fail under load every time.

pull the stack and look at the underside of the ESC board under a good light, you're looking for any component thats darker than it should be or any lifted pads. also check if your motor wires are short enough that theyre not flexing against anything causing intermittent shorts. honestly if you got it cheap enough just replace it, used ESCs are a gamble.

had almost the exact same thing happen on my first build lol. turned out i had bridged two pads on the battery lead when i was soldering the XT60 and it was arcing internally under load. couldnt even see it without a magnifying glass. might be worth double checking all your solder joints with a loupe or even just your phone camera zoomed in, you'd be surprised what you miss with the naked eye