1. Safety first
Soldering is safe when everyone follows the same rules every single time. Read this whole module before you touch an iron, and always solder with your coach or another adult in the room. If you're ever unsure whether something is safe, stop and ask.
Team rule: no batteries at the soldering bench
A drone battery is never plugged into the drone while anyone is soldering. Batteries stay with your coach, away from the soldering bench, at all times.
- You never plug in or unplug a drone battery at the bench. Your coach handles batteries.
- "The drone is switched off" or "it's disarmed" doesn't count. A plugged-in battery means the board has power, and a single solder drop can short it and start a fire.
- If you ever see a battery on the bench or plugged into a drone you're about to work on, stop and tell your coach before the iron gets near it.
- This applies to quick fixes at tournaments too.
Heat and the iron
The tip runs between 320 and 420 °C (about 610 to 790 °F). That's hot enough to burn skin instantly. The metal shaft behind the tip is just as hot, so hold the iron only by the rubber grip, like a pencil.
When you're not using the iron, it goes back in its stand, every time, even for a few seconds. Never set it down on the table. If the iron falls, let it fall and step back. Never try to catch it. Treat the iron as hot until your coach says it's cool; it stays hot for several minutes after being switched off.
Eyes
Safety glasses go on before the iron turns on and stay on until it's off. Flux can boil and spit tiny drops of hot solder, and the ends of wires you clip with cutters can fly off. Regular glasses are not safety glasses.
Fumes
The smoke from soldering comes from the flux, and it irritates your nose, throat and lungs. Turn on the fan or fume extractor before you start so the smoke is pulled away from you. Don't lean over the joint to look closer while it's smoking.
Hands and lead
No food or drinks at the bench. Wash your hands with soap when you finish, before you eat. This matters most if your team uses leaded solder. Keep fingers away from the joint: use tweezers, tape or helping hands to hold wires.
Clothes and workspace
Tie back long hair, roll up loose sleeves, and wear closed-toe shoes in case a drop of solder falls. Keep the bench tidy: the iron cord routed where you won't catch it, wire clippings swept up, and drinks well away from the board and the iron.
If you get burned
Put the iron in its stand and run the burn under cool (not ice-cold) running water for 20 minutes. Tell your coach right away, even if it seems small. Don't put ice, butter or creams on it.
Before the iron turns on
- Coach is in the room.
- No battery on the bench and none plugged into the drone. Your coach has them.
- Drone unpowered: no USB cable plugged into the flight controller either.
- Safety glasses on, hair tied back, sleeves up.
- Fan or extractor running.
- Bench clear: no loose clippings, solder scraps, drinks or food.
- Iron in its stand with the cord out of the way, then switch it on.
When you finish
- Tin the tip with a little fresh solder, then put the iron in its stand.
- Switch the iron off and leave it in the stand to cool. Never pack away a warm iron.
- Sweep up wire clippings and solder scraps into the trash.
- Glasses off last, then wash your hands with soap.
2. Tools and materials
You don't need an expensive station, but you do need temperature control. The cheap fixed-temperature pencil irons run too cool for battery pads and too hot for signal pads, which is exactly the range drone work spans. A smart pen iron like a Pinecil or TS101 on a USB-C PD supply, or a bench station like a Hakko FX-888D, covers everything on a 20 cm drone.
| Item | What to get | Why it matters for drone soccer |
|---|---|---|
| Safety gear | Safety glasses marked Z87.1, a fan or fume extractor, an iron stand, a heat-resistant silicone mat | Required before anyone solders. Every student gets their own glasses. See module 1. |
| Iron | Temperature-controlled, 60 W or more | Battery pads sit on a large copper plane that soaks up heat; underpowered irons give cold joints there. |
| Tips | ~2 mm bevel/chisel for general work, ~3 mm chisel for battery pads | Tip contact area moves heat. A pointy conical tip is the most common beginner mistake. |
| Solder | 63/37 rosin core, 0.6–0.8 mm | Eutectic: it goes from liquid to solid at one temperature, so joints are less likely to set grainy. |
| Flux | No-clean rosin paste or tacky gel flux in a syringe | The core flux in solder burns off fast. Extra flux is the single biggest upgrade to beginner joints. |
| Tip care | Brass wool cleaner, tip tinner tin | Brass wool cleans without cooling the tip the way a wet sponge does. |
| Holding | Helping hands or a PCB vise, fine tweezers, Kapton tape | The wire must stay perfectly still while the joint cools. |
| Wire work | Flush cutters, strippers rated for 18–30 AWG, assorted heat shrink | Motor and receiver wires are thin silicone wire that tears with the wrong stripper. |
| Testing | Multimeter with continuity beep, smoke stopper | Catches shorts before the battery does. |
3. Heat, temperature and the tip
Soldering is a heat-transfer problem. Solder only bonds when the pad and the wire themselves reach melting temperature; solder dripped onto a cold pad just sits on top as a ball. Three things decide how fast heat gets in: tip temperature, tip contact area, and a thin bridge of molten solder between tip and joint. That last one is why you keep the tip tinned. A dull black tip barely transfers heat at all.
The pads also differ. A receiver pad is a tiny island of copper and heats in a second. The battery pads connect to big internal copper planes that spread the heat across the whole board, so they need a bigger tip and more temperature. Turning the iron up with a tiny conical tip doesn't fix that; the tip can't deliver the heat fast enough.
| Joint | 63/37 leaded | Lead-free (SAC305) | Tip | Dwell |
|---|---|---|---|---|
| Signal pads (RX/TX, LED, 5V) | 320–350 °C 610–660 °F | 350–380 °C | Fine bevel or 2 mm | 1–3 s |
| Motor pads | 340–370 °C 645–700 °F | 370–400 °C | 2 mm chisel | 1.5–4 s |
| Battery pads, XT30 | 380–420 °C 715–790 °F | 400–430 °C | 3 mm chisel or largest | 2.5–6 s |
Joint simulator
Pick a joint, tip and settings, then see what you'd likely get. It's a teaching model, not physics, but the failure patterns are real.
4. The wire-to-pad joint
Nearly every joint on a drone soccer build is a wire on a flat pad, and they're all made the same way: tin the pad, tin the wire, then join the two. Pre-tinning both sides means the final step only has to melt solder that's already bonded, which takes a second or two and keeps heat away from the board. The lesson video at the top of the page walks through it; here is the same sequence for reference at the bench.
- Clean and tin the tip. Wipe in brass wool, add a little solder. Shiny means ready.
- Flux the pad. A small dab, not a puddle.
- Tin the pad. Tip on the pad for a second, feed solder into the pad on the side opposite the iron, stop at a low shiny dome.
- Tin the wire. Strip 2–3 mm, twist the strands, heat from below, feed from above until the strands are just wetted.
- Join. Lay the wire on the pad, hold it still, press the tip on top until both layers melt and flow together (about 2 s).
- Lift and hold. Put the iron straight back in its stand, and don't move the wire for three seconds. The joint is still hot; don't touch it to test.
- Inspect. Shiny, smooth, concave edges, outline of the wire visible under the solder.
5. Wire prep, splices and heat shrink
Most drone wire is fine-stranded silicone wire: flexible, heat-resistant, and easy to cut by accident. Strip only as much as the pad is long, usually 2–3 mm, and check that no strands were nicked or left behind; a single stray strand touching the next pad over is a short. Twist the strands tight before tinning so they stay together.
Cut wires to length before you solder. Leave a little slack so impacts flex the wire rather than pull on the pad, but not so much that a loop can reach a prop. In a cage sport, the drone takes hits every match, and a wire pulled tight across the frame is the one that fails first.
For an inline splice (extending a motor wire, joining a pigtail), slide the heat shrink onto the wire before soldering, tin both ends, lay them side by side and melt them together, then center the shrink over the joint and shrink it with a heat gun or the barrel of the iron, not the tip. On the drone's battery lead (the loose pigtail, never a battery), offset the two splices so the red and black joints don't sit next to each other.
6. Practice drills
Do these on scrap before touching your flight controller. A cheap practice PCB kit or a dead FC is ideal. Check each one off as you pass it; the module completes when all eight are done.
7. The drone soccer build: what goes where
A Class 20 drone soccer ball typically uses an all-in-one (AIO) flight controller with the ESC built in, four small brushless motors, a receiver, an LED strip in your team color, and a battery lead. Solder in this order: receiver and LED (small, delicate wires) first while the board is easy to hold, then motors, then the battery lead last, since its thick wire makes the board awkward to position.
The battery lead you solder to BAT+ and BAT− is a loose pigtail with a connector on the end, never a battery. Nothing plugs into that connector at the bench; only your coach connects a battery, after the hand-off in module 8.
Click each pad below to see what connects there. This is a representative layout; names and positions vary between boards, so match labels to your kit's wiring diagram, not to positions on this picture.
8. Inspection and handing off to your coach
A bad joint on a motor wire costs you a match. A short on the battery pads can destroy the flight controller the moment a battery is connected. Your job is to catch both before the drone leaves your bench. Students do every step below with no battery anywhere near the drone; the first power-up is your coach's job.
- Look under magnification. A loupe or a phone camera zoomed in. Check for shiny, smooth joints, stray wire strands, and bridges between the three motor pads at each corner.
- Clean off flux. With the iron off and cool, use a little 99% isopropyl alcohol and an old toothbrush. Bridges can hide under flux.
- Tug test. A gentle pull on each wire with tweezers. Nothing should move.
- Continuity check. Multimeter on beep mode across BAT+ and BAT−, then 5V and GND. A very short chirp is normal; a steady beep means a short. Find and fix it before going any further.
- Secure the wires. Route them away from the props and the cage, and add strain relief with a zip tie or a dab of glue along the wire, not on the pad.
- Bench closed down. Iron off and in its stand, clippings swept up.
- Hand the drone to your coach and tell them it passed the continuity check.
What your coach does next
Your coach does the first power-up, away from the soldering bench, with the props off. They usually use a smoke stopper, a small fuse-like device that limits current so a hidden short can't do damage. Then they check in Betaflight that the receiver responds and that each motor spins in the right direction. If something needs fixing, your coach unplugs the battery and puts it away first, then gives the drone back to you.
9. Pit repairs and troubleshooting
Drone soccer drones crash constantly by design, so most of your soldering after the first build is repair. Start with the most likely cause in this table before you start swapping parts.
| Symptom | Most likely cause | Fix |
|---|---|---|
| Drone reboots or cuts out on hits | Cracked battery-lead joint or XT30 joint | Reflow with the big tip at 380–420 °C and fresh flux; add strain relief to the lead. Your coach checks the battery itself. |
| One motor twitches or won't spin up | Cracked or cold joint on a motor pad, or a bridge between two phase pads | Inspect under magnification, flux and reflow all three pads; clear any bridge. |
| No receiver signal, failsafe | Receiver TX/RX swapped, or the wrong UART enabled in Betaflight Ports | TX goes to RX. Swap the wires or change the UART setting. |
| LEDs dark or garbled | Data wire on the strip's output end, or LED pad not configured | Strip arrows point away from the FC; check the LED setup in Betaflight. |
| Solder won't stick to a pad | Oxidized tip, no flux, or too little heat for that pad | Clean and re-tin, add flux, move up a tip size before raising temperature. |
| Pad came off the board | Too much heat for too long, or the wire was pulled | Stop heating. Find an alternate pad or test point for the same signal; for power pads, the FC usually needs replacing. |
Removing solder. Braid gets as hot as the iron, so hold it by the spool, never the copper. Put desoldering braid on the joint, press the iron on top of the braid, and let it wick the solder up. Add flux to the braid first; dry braid barely works. To remove a wire, heat the joint and lift the wire away with tweezers rather than pulling it off.
Speed under pressure. At events you'll swap a motor between matches. Pre-tinned replacement motor wires and a clean, tinned pad turn a three-wire swap into a few minutes of work. Drill 8 practices exactly that.
Final check
Answer all of these correctly to finish the course. Wrong answers can be retried.