Blog · 2026-07-05 · Power
Wire and connectors are where your power system's paper design meets physics. Undersized wire sags like a tired battery; a bad crimp is a random-number generator. Here's how to size, choose and terminate like the robot depends on it — because it does.
It's tempting to treat wiring as an afterthought — copper is copper, right? But every centimetre of wire and every connector in a robot is a small resistor in series with something you care about, and resistors at current do two things: drop voltage and make heat. The difference between a crisp, reliable robot and one that browns out, runs warm and fails intermittently at competitions is very often not the parts list but the fifty small conductive decisions connecting it together. The pleasant surprise is how learnable this all is: one table, three connector families, one crimping lesson.
Hobby wire is sized in AWG — American Wire Gauge — and the scale runs backwards: smaller number, thicker wire. Each 3-gauge step doubles the cross-sectional area, so 14 AWG has twice the copper of 17 AWG and carries current with half the resistance. The mnemonic that makes the scale memorable: the gauge is roughly how many times the wire was drawn through dies at the mill — thinner wire, more draws, bigger number.
What limits a wire's current is heat: current through resistance makes watts, and the insulation has a temperature it will tolerate. That's why "ampacity" tables vary by context — a wire buried in a wall harness is rated far lower than the same wire in free air on a robot chassis. For short runs of silicone-insulated wire (the hobby standard, tolerant to 200 °C), sensible working figures are:
| AWG | Robot working current | Typical jobs |
|---|---|---|
| 26–24 | 1–3 A | Signals, LEDs, small sensors |
| 22 | ≈5 A | Servo extensions, small motors |
| 20 | ≈7 A | Servo power, small drive motors |
| 18 | ≈10 A | Motor branches, small battery leads |
| 16 | ≈15 A | Motor mains, medium battery leads |
| 14 | ≈20 A | Battery leads, drive mains |
| 12 | ≈30 A | Big battery leads, combat drives |
| 10 | ≈40 A+ | Heavy platforms, ESC mains |
Two refinements. First, voltage drop can bind before heat does: at low battery voltages, even a safe-temperature wire can eat meaningful volts. The math is V = I × R, with R ≈ 0.021 Ω/m for 22 AWG down to 0.005 Ω/m for 14 AWG; a metre of 22 AWG round-trip (out and back = 2 m of conductor) at 5 A drops about 0.2 V — 4% of a 5 V servo rail, gone. Thick and short beats thin and long. Second, the battery leads carry everything, so they're always the thickest wire on the robot; the Power Budget Calculator derives the gauge from your total draw automatically.
The connector zoo is vast, but a robot bench really needs three families, chosen by current.
High current — XT60. The yellow keyed connector is the hobby world's battery standard for good reasons: 60 A rating, gold-plated bullets with large contact area, impossible to reverse, and self-cleaning on each mating. XT30 (30 A) scales it down for small builds, XT90 (90 A, with an anti-spark variant that pre-charges ESC capacitors) scales up. If your batteries and robots all speak XT60, packs interchange freely and reverse-polarity accidents become structurally impossible. Retire anything arriving on a Tamiya connector — the white blocks on old NiMH packs are 15 A-optimistic with terrible contact pressure, and they're the hidden resistor behind many "weak battery" complaints. Deans/T-plug is XT60's older rival: fine if you're standardized already, not worth adopting now.
Medium current — JST families. "JST" is a manufacturer, not one connector, and the family names matter: JST-XH is the balance connector on LiPo packs; JST-PH (2 mm pitch) is the small white power plug on 1S packs and many modules; JST-SM is the inline wire-to-wire type common on LED strips; JST-VH/EL handle 3–10 A for small motor branches. Locking versions resist vibration — which describes every robot — so prefer them over friction-fit alternatives for anything that moves.
Signals — Dupont and its successors. The 2.54 mm Dupont jumper is the breadboard-era default: fine for prototyping, mediocre on a vibrating chassis where friction-fit headers walk loose. The upgrade path for permanent builds is locking 2.54 mm shells (KF2510/Molex KK style) or JST-XH used as signal connectors — same pitch, positive lock, crimped properly. Servo connectors are essentially standardized Dupont 3-pin: signal, positive, ground, with the ground wire darkest in almost every brand's scheme.
Beginners assume soldering is the "real" connection and crimping the cheap shortcut. Industry believes the opposite, and for a vibration-heavy machine like a robot, industry is right. A proper crimp is a gas-tight cold weld — the terminal's wings fold into the strands with enough pressure that the metals flow together, excluding air, with a separate insulation grip absorbing flex. A soldered joint, by contrast, wicks solder up the strands and creates a rigid section exactly where the wire flexes; the boundary between soldered-stiff and free-flexing wire is where vibration concentrates stress, and where the strands eventually fatigue and snap — hidden inside intact insulation.
Good crimps need matching parts and a ratcheting tool: the terminal sized to the wire gauge, the correct die, strip length equal to the conductor barrel, and the ratchet ensuring full compression every time (an SN-28B/SN-01BM class tool covers Dupont and JST for the price of two pizzas). The test is the tug test — a correct crimp is stronger than the wire itself. Where solder still wins: XT-family bullet cups are designed to be soldered (tin the cup, tin the wire, reflow together, heat-shrink over), and board-level connections are soldering's home turf. The rule of thumb: crimp what flexes, solder what doesn't.
Colour discipline: red positive, black ground, everywhere, no exceptions even when the "wrong" colour is closer to hand — future-you diagnosing at a competition will pay for today's shortcut. Strain relief: wires clamped or zip-tied near every connector so tugs load the tie, not the termination. Service loops: a few centimetres of slack at moving joints, routed so articulation flexes the loop, not the crimp. Twisted pairs for motor leads (cancels radiated noise) and separation between power runs and signal runs, crossing at right angles when unavoidable. Label both ends of anything that could be ambiguous. And after the first real drive: the touch test — run a finger over every connector and splice; warmth is resistance confessing, and it always confesses before it fails. A warm connector under load is dropping voltage you'll otherwise chase as the "sag" described in Voltage Sag and Brownouts.
Two identical wires in parallel genuinely halve resistance — it's electrically legitimate, and 3-gauge math means two 20 AWG ≈ one 17 AWG. It's fine as a field expedient; as a design choice it doubles the terminations that can fail, so buy the right gauge for permanent harnesses.
Stranded, always, for anything on a robot — solid wire work-hardens and snaps under vibration. Solid core belongs in breadboards and wall buildings, neither of which accelerates.
Through a distribution point — PDB pad, bus bar, or terminal block — not by splicing mid-run. Each conductor then gets a termination sized for itself, and the fuse ahead of the thin branch (sized for the thin wire) keeps a branch fault from ever asking 22 AWG to carry 14 AWG current.
A modest one-time purchase removes wiring friction from every future build. The core stock: silicone wire in 14, 18 and 22 AWG (red and black spools of each), a small reel of 26 AWG for signals, XT60 pairs by the ten-pack, JST-XH and 2.54 mm crimp kits with terminals and shells in the common pin counts, adhesive-lined heat-shrink in three diameters (the adhesive lining seals and strain-relieves in one step), and a bag of automotive blade fuses spanning 5–30 A. Tools: the ratcheting crimper, a proper wire stripper with gauge-marked notches (never the twist-and-pull-with-teeth method, which nicks strands and starts every future failure), flush cutters, and a helping-hands jig for soldering XT connectors without burnt fingertips. Total outlay is roughly the price of one mid-range servo, and the payoff is that every connection on every robot from now on is the correct connection, made in a minute, rather than whatever compromise was reachable at 11 pm the night before a demo.
Size from the table, standardize on XT60 + JST + locking signal shells, crimp what flexes, and touch-test under load. Get your robot's specific gauge and fuse numbers from the Power Budget Calculator, and see where these wires fit in the bigger architecture in How to Build a Robot Power Distribution System.