Power switches & removable links

Every combat robot must have a way to completely remove power from the outside, without tools, quickly. This is a hard rule at every event.¹

Removable link (the standard solution)

A plug that completes the main power circuit and is pulled out to disconnect.

• Carries full main-bus current — size it like the battery connector (an XT30 or XT60 doubling as the link, or a purpose-made link).
• Mounted so it’s reachable from outside the robot, clearly, in both orientations if possible.
• Retained in a socket that holds it against vibration but releases with a firm pull. A lanyard/loop makes it easy to grab.
• When out, the robot is fully dead — including weapon logic and any capacitor bleed path should discharge quickly.

High-current switches

Purpose-built combat power switches (screw-actuated or slide) are allowed by most rulesets as long as they break the full current and their state is obvious. A switch that only signals a BEC or ESC enable line is not sufficient — the main power must be broken.¹

Common beetleweight options:²

• FingerTech Mini Switch — the long-time default: a screw contact, compact, vibration-resistant. On high-voltage systems with big capacitors it can arc on turn-on and slowly erode the contacts.
• Lynx Switch — adds a precharge resistor so the capacitors charge gently before the contact closes; solves the arcing.
• Puppy Power Switch — bulkier, higher current, spring-loaded fail-ON so a hard hit can’t switch the robot off mid-match.
• Several combat power-distribution boards integrate a screw switch.

Wire the switch on the negative side. In a screw switch the tool becomes part of the circuit; on the positive side it can go live and short to a conductive (e.g. carbon-fibre) chassis. Never connect both battery leads to the switch.²

What it must isolate

• Drive motors,
• weapon motor,
• receiver / BEC,
• any lights, pumps, or accessories.

Basically: link out → nothing on the robot can move or power up.

Placement and protection

• Not behind the wedge or under the robot where it can’t be reached.
• Protected from weapon debris and impacts so it can’t be knocked out mid-match (which would be a safe failure) or jammed in (unsafe).
• Label the direction to remove it if it isn’t obvious.

Master power vs weapon lock

The removable link is separate from a weapon lock — a physical device that stops the weapon moving while you handle the robot. Most rulesets require both. A good weapon lock is one-handed to fit and remove, obviously visible, and can’t fall out on its own or when the weapon pushes against it.¹²

Common spinner locks:²

• A C-clamp, spring clamp, or locking pliers on the rotor — quick, but clamp it through a hole in the weapon so it can’t shake off.
• A pin through the chassis into the weapon’s path — a screwdriver works; a ball-lock pin is the secure, easy version.
• A 3D-printed block shaped to jam between chassis and rotor.

Lifters and other high-torque arms need a pin that locks the whole mechanism, not just a stop against rotation. In the pits, cover forks and teeth with foam cubes or printed guards.

References

Footnotes

1. SPARC Robot Construction Specifications (Standardized Practices for the Advancement of Robot Combat), v1.4, 2023 — §“Power System” and §“Safety”. Section numbers vary by revision; check your event’s adopted version. ↩ ↩² ↩³

2. Ping, L., with L. Skotiniotis, I. Talbert & D. Tran. Beetleweights for Dummies (Fall 2025 revision) — builder-maintained beginner guide distributed via the NHRL Discord. Sections: Electronics & Wiring → Switches; Testing & Safety → Weapon Locks. ↩ ↩² ↩³ ↩⁴