Combat robots need more than armor and a powerful weapon to enter a competition safely. The essential safeguards are a reachable master power cutoff, a radio-control failsafe, a positive weapon lock, and covers for hazardous edges during handling. Competitors must also meet rules for batteries, high-voltage systems, testing, protective equipment, and restricted weapons. Exact limits vary by organizer and weight class; the inspector for the event you enter has final authority.
Start with the event’s rulebook, not a generic checklist
Robot-combat safety is rule-driven. A three-pound plastic spinner, a 30-pound lifter, and a flame-equipped heavyweight do not present the same hazards, so organizers apply different requirements to each. Before designing a chassis, download the current rules for the specific event, division, and weapon category. Confirm the rule version and effective date, then ask the organizer about anything described as restricted or requiring approval.
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NHRL’s 2026 Open Rules provide a detailed example, but their timings and class limits are not universal. BattleBots lists its Design Rules and Tournament Rules as version 2027.01, updated October 1, 2026, and notes that a 2027 draft is available. That difference alone shows why a robot approved at one competition cannot be assumed eligible at another.
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| Safety feature | What it controls | NHRL 2026 requirement |
|---|---|---|
| Master power cutoff | Drive and weapon power | Accessible without disassembly, operable with one hand, and able to deactivate the robot within 15 seconds |
| Radio failsafe | Unintended operation after signal or transmitter loss | Drive stops within 30 seconds and weapons within 60 seconds; complete system must pass an inspector-supervised test |
| Weapon lock | Movement, ignition, extension, rotation, or projectile release outside the arena | Positive physical restraint with a visible warning tag; movement allowances depend on weapon type |
| Edge and point covers | Accidental cuts or punctures while carrying the robot | Required over edges or points that could readily cause a serious injury during handling |
Treat these as systems rather than individual parts. A switch advertised as a cutoff or a receiver marketed with failsafe capability is not automatically compliant. The installed wiring, software settings, mechanical lock, labels, and inspection procedure must work together.
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How to design the master power cutoff
What the cutoff must disconnect
The master cutoff must remove power from both the drive and weapon systems. If lights, sounds, fans, or another circuit remain energized, the robot can appear inactive while a dangerous subsystem is still live. Design the circuit so the cutoff is the authoritative “safe” state, not merely a controller reset.
Access and operation
NHRL permits a switch or a removable link. It must be reachable without taking the robot apart, actuated with one hand, and deactivated within 15 seconds. Put it where an inspector can reach it in the robot’s normal fighting orientation, and leave enough clearance for a gloved hand or a tool-free grip if the event requires one.
Weight-class details
- For three-pound robots, a battery connector may serve as the removable link.
- For 12-pound and 30-pound robots, use a dedicated removable link with adequate strain relief.
- For 12-pound and 30-pound entries, the cutoff must be accessible in the primary fighting orientation.
Build the cutoff into the chassis rather than adding it as an afterthought. During inspection, be prepared to remove or open nothing except the permitted link and to demonstrate that drive and weapon power both disappear.
Configure and prove the radio failsafe
What a failsafe does
A failsafe commands the robot to stop when communication is lost or the transmitter is powered down. It protects handlers when a transmitter battery dies, a radio link is interrupted, or an operator accidentally turns off the controller. NHRL’s 2026 rules require drive motion to stop within 30 seconds and weapon motion within 60 seconds after either trigger.
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Requirements beyond a receiver feature
NHRL requires a dedicated receiver for each robot and for each multibot segment. An autonomous robot still needs a radio-control system for remote activation and deactivation. A receiver’s product description cannot establish compliance: the event tests the complete installed transmitter, receiver, controller, motor, and weapon chain.
A practical pre-inspection test
- Charge the transmitter and robot batteries to the condition required by the event.
- Place the robot in a secured test area with the weapon restrained and no person in its operating path.
- Arm the control system according to the event’s procedure and verify normal drive and weapon commands.
- Switch off the transmitter, remove its battery, or otherwise create the organizer’s specified signal-loss condition.
- Measure the time until drive motion stops and the time until weapon motion stops.
- Restore the link, repeat the test, and record the result so you can reproduce the configuration at inspection.
NHRL states that “Robot control and communication systems must pass a fail-safe test overseen by a Safety Inspector at Safety Inspection to compete.” Plan to demonstrate the actual robot, not a bench receiver or an unpowered mock-up.
Use a positive weapon lock whenever the robot is outside the arena
What must be restrained
A weapon lock prevents dangerous actuation, extension, rotation, ignition, or other movement while the robot is being carried, stored, inspected, or transported. The requirement applies to more than conventional spinning weapons. A lifter, including a CAM lifter, can create a crushing or pinch hazard and therefore needs a restraint. Meltybrain designs need wheel locks or covers. A projectile system needs a physical method that prevents a projectile from being expelled.
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Under NHRL’s 2026 rules, a lock on a rotating kinetic weapon may allow no more than 180 degrees of movement. A non-kinetic weapon may allow no more than 15 degrees, and any remaining movement must not create a pinch hazard. The lock should hold the mechanism against the forces generated by carrying, bumping, or an accidental control command; software-only “safe” modes are not a substitute for a physical restraint.
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Make the lock obvious and safe to install
Attach a sturdy, clearly visible tag marked “Weapon Lock,” “Remove Before Fight,” or equivalent. NHRL specifies minimum tag dimensions and requires insertion with one hand while keeping fingers out of the weapon’s path. The lock should remain installed whenever the robot is handled outside the match or inspection activity that the organizer specifically permits.
Special cases: flames, heat, and sparks
Flame systems require organizer approval for their lock arrangement. Possible methods include an inline valve, a switch, or a physical block, but the event must accept the design. Cover exposed hot-surface igniters and spark gaps so a handler cannot touch them or accidentally trigger ignition while the robot is locked.
Cover hazardous edges before moving the robot
Edges and points that could easily cause a serious accidental cut or puncture must be covered while the robot is moved around the venue. These covers are a handling and transport control, not a change to the robot’s fighting geometry. Keep them installed in the pits, queueing areas, inspection line, and loading areas unless the organizer directs removal for a specific test.
Choose covers that cannot fall off when the robot is lifted. Bright color, a tether, or a label helps handlers identify them, but visibility does not replace a secure fit. Include every exposed blade tip, tooth, wedge corner, and sharp frame feature that can injure someone who is carrying or reaching around the robot.
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Meet electrical and battery requirements
Nominal voltage
NHRL limits nominal battery voltage to 75 volts unless the organizer gives explicit approval. Any system that produces voltages above the applicable battery limit may require additional inspection. Document the battery configuration, maximum charged voltage, wiring, fusing, and accessible disconnect so the inspector can verify what the robot actually contains.
Charging lithium-chemistry batteries
NHRL requires lithium-chemistry batteries to be charged with balance leads, and charging must be attended. Do not leave a pack charging while the pits are unattended. Use the event’s approved charging area and containment process, inspect packs for swelling or damage, and isolate a suspect battery instead of connecting it to a charger.
Power isolation during service
Before changing a motor, opening an electronics enclosure, or reaching near a weapon, remove the master link or switch off the cutoff and verify that stored energy has dissipated. Capacitors, pneumatic reservoirs, hydraulic accumulators, and hot surfaces can remain hazardous after battery power is removed; follow the event’s discharge and depressurization procedure for those systems.
Identify restricted and prohibited weapon systems early
Features that need advance review
NHRL’s 2026 rules call for organizer approval or additional conditions for pneumatic and hydraulic systems, certain exposed moving components above 300 mph, and designated combustion, flame, heat, projectile, inductive, or electromagnetic designs. If your concept includes one of these features, start the review at least four weeks before the competition so staff can complete their review no less than three weeks before the event.
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Send a clear technical package: energy source, maximum pressure or voltage, moving-part speed, containment, ignition or firing method, lock design, failure modes, and a drawing showing how handlers remain outside the hazard zone. Written approval is safer than relying on a verbal assumption at check-in.
Examples of prohibited systems
NHRL prohibits rocket motors, fireworks, radio jammers, and systems intended to harm people outside the cage. Its rules also address entanglement devices, arena-fouling materials, and other hazards. A design that is legal in one league may be banned in another, so compare the exact rule language before purchasing parts or machining a frame.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Make testing and workshop behavior part of the safety design
Hardware safeguards cannot compensate for an unsafe test area. NHRL states: “All robot weapon and drive testing must be done in a test box.” The rule applies to routine drive checks as well as full-speed weapon tests, subject to a narrow wheels-up exception. Use the organizer’s approved enclosure, keep spectators and other teams outside it, and remove the weapon lock only when the authorized test procedure calls for it.
Recommended Free Tools
Wear safety glasses and other appropriate personal protective equipment when using power tools in the pits or machine shop. Secure loose clothing and hair, clamp workpieces, disconnect battery power before drilling or cutting near wiring, and keep a second person informed when a charged robot is being serviced. Follow venue rules for grinders, welding, compressed gas, and fire response in addition to robot-specific rules.
A build-to-inspection workflow
- Freeze the rule set. Record the organizer, event date, weight class, weapon category, and rule version. Recheck for amendments before travel.
- Map every energy source. List batteries, capacitors, pneumatic or hydraulic storage, hot surfaces, projectiles, and rotating parts. Give each source a cutoff, restraint, or containment method.
- Install the master cutoff. Verify one-hand access, no-disassembly access, strain relief, and complete removal of drive and weapon power.
- Configure the radio system. Use the required receiver arrangement, set loss-of-signal behavior, and test transmitter shutdown with the finished wiring.
- Fabricate and label locks. Check movement limits, pinch points, one-hand insertion, tag wording, and retention during carrying.
- Add edge covers. Fit covers to every serious cut or puncture hazard and tether them if they could be lost.
- Submit restricted features. Send drawings and hazard details by the organizer’s deadline; do not wait for event-day inspection.
- Rehearse inspection. Have the robot in its primary fighting orientation, bring the lock and cutoff tools, and be ready to demonstrate failsafe, power isolation, and safe handling.
How to compare two competitions’ safety rules
| Comparison point | Questions to ask |
|---|---|
| Cutoff | Is a switch, removable link, or connector allowed? How quickly must it deactivate, and where must it be reachable? |
| Failsafe | What event triggers it? Are drive and weapon stop times different? Is an inspector-supervised test required? |
| Radio architecture | Does each robot or multibot segment need a dedicated receiver? Are autonomous entries still required to have radio control? |
| Weapon lock | What movement is allowed, what tag wording and dimensions are required, and how are flame or projectile systems restrained? |
| Handling covers | Which edges need covers, and when may they be removed? |
| Electrical limits | What nominal voltage, battery chemistry, charging supervision, and containment rules apply? |
| Restricted designs | Which pneumatic, hydraulic, high-speed, thermal, projectile, electromagnetic, or entangling features need approval, and what is the deadline? |
| Testing and PPE | Is a test box mandatory? What eye, hand, hearing, respiratory, or clothing protection is required in pits and workshops? |
| Inspection authority | Who can reject a design, what evidence must be shown, and is written pre-approval available? |
Common inspection failures and their fixes
- The cutoff is buried under armor: redesign an access panel or relocate the link so it is reachable without disassembly.
- The cutoff kills the controller but not the weapon: rewire it to isolate every drive and weapon power path, then prove the result with the robot powered.
- Failsafe was tested on a spare receiver: repeat the test with the exact transmitter, receiver, firmware, motor controller, and weapon controller installed for competition.
- The lock leaves a crushing gap: redesign the stop so residual movement cannot pinch fingers and keep the tag visible from outside the hazard area.
- Sharp covers fall off: add a positive retention feature or tether and test handling from several orientations.
- A restricted weapon was disclosed too late: pause fabrication or obtain written guidance immediately; do not assume an event-day exception.
- Battery charging is unattended: move charging to the approved supervised process and use balance leads for lithium packs.
- Testing occurs outside the box: stop the test and move it to the organizer’s designated enclosure, even for a low-power spin check.
What “ready to compete” really means
A competition-ready robot is one that can be made harmless quickly, stays harmless when communication fails, and cannot actuate while handlers are exposed to it. The design must also fit the event’s electrical limits, battery procedures, weapon approvals, testing enclosure, and PPE rules. Build those controls into the robot from the first CAD revision, document them, and practice demonstrating them. The current rulebook and the event safety inspector—not a generic combat-robot checklist—decide whether the entry may compete.
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