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There is no universal answer to what a combat robot may weigh, which weapons it may use, or how it must be made safe. The organizer, event format, season, class definitions and inspection rules control. SPARC Robot Construction Specifications v1.4, NHRL’s 2026 Open Rules and an event’s own notices use different limits and procedures, so treat the current rulebook and the event inspector as the final authority.
This guide explains how to read those differences, plan a legal weapon, and prepare a robot that can pass inspection without creating hazards in the pits or arena.
What makes a combat robot legal?
Competition legality is a stack of requirements rather than a single weight number. Before building, identify the exact event and season, then obtain its current construction, tournament, battery and safety documents. Check five items together:
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- Class limit: the maximum mass for the class, including the event’s stated weigh-in configuration.
- Locomotion category: wheels, rolling shufflers, walkers and other non-wheeled designs may have different allowances.
- Weapon category: active-weapon, spinner, Sportsman, open-air and modular-weapon provisions can differ.
- Safety hardware: weapon locks, drive and weapon cutoffs, access requirements and inspection demonstrations.
- Operational procedure: where testing, charging, fuel or pneumatic work and robot movement are permitted.
A design can satisfy one of these and still fail another. For example, a robot under the nominal class weight may be rejected if its weapon module was not declared, its cutoff cannot be operated as required, or its weapon is outside the class’s speed or approval limits.
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Weight classes are not universal
Weight-class names are shorthand, not a worldwide standard. SPARC Robot Construction Specifications v1.4, dated 8 October 2023, lists classes from 0.33 lb (150 g) through 250 lb (113.4 kg). NHRL’s 2026 Open Rules run 3 lb, 12 lb and 30 lb classes. A 3 lb entry in one league therefore does not automatically have the same bonus, weigh-in procedure or eligible robot type as a 3 lb entry elsewhere.
SPARC base classes
| SPARC class | Metric equivalent | Qualification |
|---|---|---|
| 0.33 lb | 150 g | Base class listed in SPARC v1.4 |
| 1 lb | 454 g | Base class listed in SPARC v1.4 |
| 2.2 lb | 1 kg | Base class listed in SPARC v1.4 |
| 3 lb | 1.36 kg | Base class listed in SPARC v1.4 |
| 6 lb | 2.72 kg | Base class listed in SPARC v1.4 |
| 12 lb | 5.44 kg | Base class listed in SPARC v1.4 |
| 15 lb | 6.8 kg | Base class listed in SPARC v1.4 |
| 30 lb | 13.61 kg | Base class listed in SPARC v1.4 |
| 60 lb | 27.22 kg | Base class listed in SPARC v1.4 |
| 120 lb | 54.43 kg | Base class listed in SPARC v1.4 |
| 220 lb | 99.79 kg | Base class listed in SPARC v1.4 |
| 242.5 lb | 110 kg | At publication, the specification footnote said this class was exclusive to Robot Wars |
| 250 lb | 113.4 kg | At publication, the specification footnote said this class was exclusive to BattleBots |
Those are specification values, not proof that every current event offers every class. SPARC also gives separate allowances for rolling shufflers and non-wheeled robots. In its 3 lb row, for example, the allowance is 4.5 lb for a rolling shuffler and 6 lb for a non-wheeled robot. Other rows have their own table entries; do not extrapolate the 3 lb example into a general multiplier.
NHRL classes and separate bonuses
NHRL’s 2026 Open Rules identify 3 lb, 12 lb and 30 lb classes. NHRL defines its own bonus and exemption criteria, which must not be substituted with a SPARC formula. A robot’s category depends on the event’s definitions, not on what the builder calls it in a registration form.
| Rule set | Classes identified in the cited rules | How to interpret the number |
|---|---|---|
| SPARC v1.4 (8 October 2023) | 0.33, 1, 2.2, 3, 6, 12, 15, 30, 60, 120, 220, 242.5 and 250 lb | Base classes with separate locomotion allowances in the specification |
| NHRL 2026 Open Rules | 3, 12 and 30 lb | Event classes subject to NHRL’s own bonus, exemption and weigh-in rules |
How to compare two events correctly
- Write down the base class limit in the current rulebook, including the metric value and whether batteries, armor and interchangeable modules are included at weigh-in.
- Read the definitions for wheels, shufflers, walkers and other locomotion. Similar-looking mechanisms may receive different treatment.
- Check bonus and exemption eligibility instead of assuming a percentage allowance.
- Confirm the weigh-in configuration, timing and registration status for the specific event. A class listed in a general rulebook may not run at every tournament.
- Ask the inspector about any interpretation that affects your design before you buy parts or machine armor.
Weapon rules depend on format and class
There is no universal list saying that every flame, projectile, entangler or spinner is legal or illegal. The same mechanism can be treated differently in a Sportsman class, an open-air event or an event that requires an active weapon. Submit unusual concepts early, with drawings and operating details, rather than relying on an internet summary.
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SPARC examples: Sportsman and open-air formats
SPARC v1.4 illustrates why the format matters. In Sportsman classes, devices rotating more than 360 degrees are limited to a tip speed at or below 20 ft/s. The specification includes provisions for some saw and drilling devices, and it allows organizer approval for weapons that exceed the ordinary limit. An organizer may further limit or disallow a weapon judged excessively destructive.
For open-air combat, SPARC separately states a 20 ft/s absolute maximum for slow spinners. Certain systems capable of tearing pieces from an opponent require organizer clearance. These are SPARC provisions, not a universal combat-robot standard and not a guarantee that a particular event uses the same definition of slow spinner.
NHRL active-weapon and module requirements
NHRL’s 2026 rules take a different approach. A legal mechanism is not enough for scoring if the robot does not intentionally and effectively use its weapon. NHRL explains that the weapon must cause harm and affect the state of the fight; it does not have to be capable of destruction. A device that technically moves but cannot meaningfully influence an opponent may therefore fail the active-weapon expectation.
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NHRL requires weapon modules to be declared at safety inspection. Officials can require weapon locks to be demonstrated. If you plan interchangeable drums, forks, saws or other modules, list every configuration required by the event and design each one to meet the same lock, cutoff and containment rules.
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Questions to answer before proposing an unusual weapon
- What is the stored energy, rotational speed and likely failure path?
- Can fragments, hot material, fluid, flame or compressed gas leave the intended containment area?
- Does the class impose a tip-speed ceiling or require organizer approval?
- Is the weapon genuinely active and capable of affecting the fight, or merely decorative motion?
- Can the weapon be mechanically locked, electrically isolated and inspected without ambiguity?
Safety hardware required before an event
Install and carry a visible weapon lock
SPARC says harmful moving weapons must have a clearly visible locking device whenever the robot is outside the arena. The lock must use a high-visibility color and fit securely. SPARC also requires locking pins when weapon power is applied during a robot power-on procedure. Use a captive or otherwise retained device that cannot fall out during handling, and make its installed and removed states obvious to an inspector.
NHRL rules also define weapon-lock handling for its events and may require a demonstration. A software disable, radio switch or unplugged transmitter is not a substitute for the mechanical restraint required by the event.
Provide accessible power cutoffs
NHRL requires cutoffs for both drive and weapon systems and specifies accessibility and operation requirements. The exact placement, labeling and activation test are event-specific. Build the cutoff so an official can reach it without placing a hand near a weapon, then verify that it removes the intended energy rather than merely stopping a control signal.
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Separate drive and weapon power during inspection
Design your wiring and switches so officials can identify drive isolation and weapon isolation independently. Label connectors, fuses and switches; protect exposed conductors; and ensure that removing the weapon cutoff cannot unexpectedly energize another actuator.
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Testing, pits and workshop procedures
Use the event’s test enclosure
At NHRL, drive and weapon testing takes place in a test box. The stated wheels-up exception applies to robots with a second dedicated weapon switch. NHRL prohibits driving around the pits or venue. Do not treat a brief “just checking steering” movement as harmless; a radio fault or software error can turn it into a runaway robot.
SPARC’s warning is blunt: “Runaway bots are VERY dangerous.” The practical response is to test with the weapon physically locked, the robot restrained when appropriate, a clear exclusion zone and a person assigned to the cutoff.
Use personal protective equipment and designated hazard areas
NHRL requires safety glasses and appropriate personal protective equipment when using power tools. Spark- or dust-producing tools are limited to designated areas. Fuel and pneumatic loading or unloading must take place at the event’s Robot Hazard Station. Keep batteries, compressed gas, fuels and sharp spare weapons organized so that a dropped part or damaged pack cannot become a second hazard.
Prepare for inspection before arrival
NHRL requires inspection before a robot’s first fight and may ask you to demonstrate relevant safety features. Bring the robot’s wiring diagram, module list, lock pins, cutoff labels and any organizer approval in a form the inspection team can quickly verify. If a design has a novel actuator, stored-energy system or detachable weapon, contact officials before the event rather than waiting at the inspection table.
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A practical compliance workflow
- Choose the event and edition. Record the organizer, event date, class and format. Do not build from an old PDF without checking its revision date.
- Freeze the ruleset. Download the current construction, tournament, battery and safety documents named by the organizer. Note which documents are drafts and which govern the event you entered.
- Calculate mass by configuration. Weigh the complete robot, every declared weapon module and the configuration used at weigh-in. Leave margin for fasteners, labels, lock hardware and replacement parts.
- Classify locomotion honestly. Determine whether the rulebook treats your mechanism as wheeled, a rolling shuffler, a walker or another non-wheeled category. Request a written interpretation if the answer changes your allowance.
- Characterize the weapon. Document speed, tip speed where applicable, energy source, containment, intended effect and failure modes. Submit systems needing approval well before registration closes.
- Build safety controls into the design. Add visible mechanical locks, independently accessible drive and weapon cutoffs, guarded connectors and clear labels.
- Test under controlled conditions. Use the organizer’s test box or designated area, keep locks installed until the robot is in the permitted test position, and never drive in prohibited pit or venue areas.
- Run an inspection rehearsal. Have a teammate operate every cutoff and install every lock while another person checks that the robot is fully de-energized. Pack PPE and hazard-station supplies.
- Recheck immediately before travel. Rules can change, classes can fill or be canceled, and an organizer can issue a safety notice after your design is complete.
How to handle changing rules
The official BattleBots rules page says rule documents may be updated at any time. As of the cited 16 October 2026 status, it labels Design Rules Version 2027.01 and Tournament Rules Version 2027.01 as draft material, each last updated 10/01/2026. Battery rules are listed separately as Version 2020.0, last updated 09/30/20. Draft documents are useful for planning but should not be treated as operative instructions unless the organizer confirms that they govern your event.
SPARC v1.4 is dated 8 October 2023, while NHRL’s cited rules and judging Q&A are from 2026. That difference does not make one system universally newer or superior; it means you must apply the document belonging to your event. Keep a copy of the exact revision used for your design review and ask the event inspector about later amendments.
Common failure modes and fixes
| Problem | Why it happens | Fix |
|---|---|---|
| Assuming every 3 lb class is identical | Class names look standardized, but bonuses and definitions differ | Use the event’s own class, locomotion and weigh-in provisions |
| Using a SPARC allowance at NHRL | Builder carries a familiar formula to another league | Apply NHRL’s 2026 bonus and exemption criteria instead |
| Declaring only the main weapon | Interchangeable modules are treated as accessories | Declare every weapon module required by the event and present each for inspection |
| Relying on a transmitter switch as a weapon lock | Electrical disable is confused with mechanical restraint | Install the specified visible lock and demonstrate it to officials |
| Testing in the pits | Short drive tests seem low risk | Use the designated test box or approved area; follow wheels-up exceptions exactly |
| Waiting until inspection to ask about approval | Unusual designs are difficult to evaluate quickly | Send drawings, speeds and hazard controls to the organizer in advance |
FAQ
Frequently Asked Questions
Why can a robot exceed the number in its class name?
Some rule sets grant locomotion-based allowances or specific exemptions. The allowance belongs to the event’s definitions and weigh-in procedure; it is not a general permission to add weight.
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Ask the organizer or head inspector which dated document and amendment control your event, and keep that answer with your registration records. Do not rely on an older PDF or an informal assumption.
Can an active weapon be legal but still hurt my score?
Yes. In NHRL’s 2026 judging guidance, the weapon must be intentionally and effectively used to cause harm and affect the fight. Merely having a mechanism that moves is not enough.
The Bottom Line
Pick the event first, apply only its current class and weapon definitions, and design safety controls that an inspector can see and operate. A conservative reading of the rulebook, early approval for unusual weapons, visible mechanical locks, independent cutoffs and controlled testing prevent most avoidable failures.
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