Wiring and Soldering

Good wiring is invisible: it just works, match after match. Bad wiring causes many of the failures you'll see at events – robots that die after a hit, short circuits, and even battery fires. This page covers wire sizes, how to lay out and protect wiring, soldering, and the safety rules for power switches and lights. See also Connectors, Switches, ESCs, Battery eliminator circuit (BEC) and Batteries.

A typical insect-class wiring layout

Most small robots are wired like this:

Battery → power switch or removable link → ESCs (one per motor, or a dual ESC) → motors

The receiver is usually powered from an ESC's built-in BEC, and connects to each ESC's signal lead.

A power light shows when the main power is on.

Some small robots use all-in-one boards that combine the receiver and ESCs. Whatever the layout, wire everything to a common ground. Taking the receiver's ground from somewhere else (such as a balance lead) can short out part of the battery.[1]

Wire

• Use stranded, silicone-insulated wire. It's flexible and survives heat and vibration. Never use solid-core wire in a robot.
• Size it for the peak current. Combat robots draw big currents in short bursts, and the thinnest wire in a circuit has to carry it. As a rough guide, 22 AWG is conservatively good for about 7 A, and each 3-gauge step thicker roughly doubles the capacity.[2][3] Rough starting points:
  • 150 g robots: 22–24 AWG for drive motors.
  • 1 lb robots: at least 18 AWG (or doubled 22 AWG) from the battery to the ESCs.
  • 3 lb robots: around 16–18 AWG for the main power and weapon.
  • 12–30 lb robots: around 12–14 AWG for the main power and weapon.

Always check your ESC and motor specifications.

• Keep wires as short as practical. It saves weight and leaves less to snag.

Layout and protection

• Keep wires away from weapons, moving parts and sharp edges. A common failure is motors or weapons cutting through wires after a few hits.[4]
• Secure wires so they can't move around during hits. Tie them down near the receiver, and a little hot glue at connectors helps keep them from pulling out.[5]
• Strain relief: make sure a pull on a wire is taken by the wire's mounting, not the solder joint.
• Mount switches and connectors mechanically, not just by their solder joints. One university team found their main switch had come unsoldered and was held only by heat-shrink.[6]
• Insulate everything, especially near metal frames. Exposed wire and battery terminals touching a metal chassis are a classic cause of shorts.
• Check your wiring before every power-up. A short can get hot very quickly.

Soldering

• Use a decent temperature-controlled iron (see Tools For Beginners) with a tip big enough for the job. Heavy wire and connectors like XT60s need a large chisel tip and plenty of heat.
• Use flux and tin both the wire and the connector first. Solder should flow into the wire strands, leaving a smooth, shiny joint – not a dull blob.[7]
• Slide heat-shrink on before you solder (it's a common mistake to forget), and keep it away from the heat until the joint is done.
• When soldering plastic-bodied connectors like XT30s and XT60s, plug in a mating connector while you work so the pins stay aligned if the plastic softens.
• Trim stray strands, which can poke through heat-shrink and cause shorts.
• Double-check polarity before plugging in a battery – reversed polarity can destroy ESCs instantly.[8]

Power switches, lights and fuses

• SPARC requires a mechanical disconnect for the main power – a switch or removable link – that can be operated within 15 seconds without danger. Relays can be used but don't replace it. The whole robot must be fully switched off within 60 seconds. See Switches.
• SPARC also requires a power light that's easy to see from outside the robot.[9] (NHRL doesn't require a light, but wants the switch to cut all power, including any lights.[10])
• Protect the battery terminals from short circuits.
• Fuses: neither SPARC nor NHRL requires them, and experienced builders advise against fusing ESCs and motors in a combat robot – a fuse that blows mid-match loses you the fight. A single main fuse to protect the battery from a dead short is the only one sometimes recommended, and some events require it.[11]

Further reading

• Melbourne Combat Robotics – How to wire up your combat robot (video)
• Ask Aaron – Radio and electrical (Team Run Amok)
• PowerStream – wire gauge and current table
• Safety and Failsafes
• Troubleshooting – finding brownouts, shorts and intermittent faults