#FPV

Four 4S packs, under 60 apiece. Welding was the easiest step; getting the balance lead wiring order right was what really strained my eyes. My palms were soaked with sweat on the first flight. Crashed once and broke a prop, but the pack came through fine. To anyone wanting to get into it: learn spot welding first, and everything after that is just saving money.

Unboxing the AWithZ U3 spot welder, a common tool for RC car folks: looks like a power bank, two gold-plated sockets for the welding pens, USB output doubles as a power bank, Type-C charging, 11000mAh 3.7V, ‘pioneer of small portable spot welders’; the manual matters (welding method, settings tutorial, weldable nickel / copper thicknesses); the accessory bag has two welding pens, a USB cable and a small pack of nickel strip. Use: DIY 18650/21700 series / parallel. Example, Lao Gao’s radio (Hello Radio V14) 18650 battery: before the welder he used a cell box + XT30 soldered to main + / −, charging through the balance plug was too slow, so parallel-connect an XT30 + XT60-to-XT30 to a charger for fast charge; with a spot welder no cell box is needed. Series / parallel joins on the 18650’s end metal with solder are very hard, and the heat easily damages the cell internals, so get a small spot welder, a hundred-odd yuan, two quick pops. Method: fix the cell, cut strip to length, round off sharp corners (to avoid piercing the heat-shrink); long-press to power on, push the pen pins in firmly; manual mode (press the switch on the pen, pop, welded; auto fires when the two pens touch); preheat 2 milliseconds, interval 2 milliseconds; gear turned down from 65 to 5 is enough; multi-pulse once; one pen presses while the other welds, two spots at gear 5 are already solid, four spots per 18650 (two presses) is very secure; tack the other cell’s positive, + and − joined. One 18650 is 3.7V, multimeter on DC reads 8.06V total, proving the series join. Main + and − on the front also get nickel strip: solder won’t take, the positive is an aluminium plate with a dense oxide layer that won’t tin, the negative can be soldered; once the aluminium is ‘converted’ to nickel it tins easily (comment: just file it and it’ll solder → ‘if it blows up from filing, go find him’). Balance leads to the middle strip between the two cells and to both ends; 2S done; fish paper works for insulation, Lao Gao wraps both ends in EVA foam then shrinks the film; bus reads 8-point-something volts, balance port 4.048/4.039V, normal. FPV pilots like fast charging, so the XT30 goes to an RC plane / car charger. A spot welder is a must for 18650 DIY, don’t go dumbly soldering 18650s with a big iron, too hot and risky. Comments: can you talk slower (no, 1.5× speed); soldering the voltage feedback on would be handier; where does the middle of the three 2S balance wires go; so easy, the iron always shorted before; bought a welder, time to hand-build an EV.