Safety is always the #1 priority at all times when it comes to robot combat. While things may look dangerous and exciting in the cage, we need to ensure that that excitement actually stays in the cage. Below you can find some safety information related to combat robotics.

The basic rules...

  • All robots must have a weapon lock that prevents any spinning weapons from moving outside of the cage.
  • All robots must have a way to turn off power without disassembling the robot.
  • All robots must pass a radio fail safe test.

Fighting robots are inherently dangerous. Safety is paramount. We require that all competitors abide by all the safety rules for their weight class. This is not just for your safety but everyone else's as well. Safety violations can occur for:

  • Improper or non-use of weapon lock
  • Unsafe weapon tests with box open
  • Unsafe touching of the bot (grabbing an unlocked weapon)
  • Improper load-in procedure
  • Pit safety issues such as open test box testing, driving in pits, weapon test on table, etc

We will use an escalating system of consequences: These reset each event.

  • 🟨 1st issue: Yellow Card: Warning
  • 🟧 2nd issue: Orange Card: Match forfeit
  • 🟥 3rd issue: Red Card: Event forfeit
  • ⬛️ 4th issue: Black Card: Year forfeit

Each of these levels comes with a chat about what happened and how to improve safety.  We 100% understand that accidents happen, especially under stress.  If you get a card, please don't panic.  It's not a sleight on you personally.  We will do everything that we possibly can to make sure that we work together to correct the safety issues in question.  As a competitor myself, the absolute last thing I want to do is tell a competitor they can't compete.  However, if said competitor is putting themself or others in danger, we need to make sure those issues are corrected.  

Weapon Locks

A weapon lock is anything that will keep your weapon from being dangerous when your robot is not in the ring. Weapon locks are required during loading and unloading into the ring or test boxes. Robots that don't use a weapon lock are a hazard to everyone at NHRL and are not allowed. Failure to follow rules will result in a verbal warning and a second failure will result in your robot being disqualified from the event for the day. If you have questions don't hesitate to ask the staff. Everyone is friendly and supportive, safety is just very important.

When must a weapon lock be used

  • During robot load-in to the cage or test box
  • Anytime your robot is powered up anywhere at NHRL

What works well as a Weapon Lock

  • A metal pin or plug that prevents any rotating weapon from spinning, ideally painted a bright color.
  • A plastic cover (pool noodles work well) over any sharp blade on your robot

What isn't great as a weapon lock

  • Using a tool such a vice grips is frowned upon as a weapon lock.
    • Weapon locks should be a dedicated item and not something that could be confused in any way.
  • Anything that can easily fall out or be dislodged
  • Your hand or any other part of your body

Battery Safety

Batteries, if mishandled or damage, present a fire hazard. Please be sure to inspect your batteries thoroughly before each use;

Signs that a battery has reached the end of its life:

  • Any battery that has sustained damage or cuts to the metal foil that holds the cells.
  • Puffy batteries. Batteries that are starting to fail will start to fill with hydrogen gas. This will make the battery puffy. A little puffy is likely OK for a few more matches.. but a very puffy battery is no longer safe
  • Batteries which cannot be charged. If the charger rejects the battery due to bad cell voltage its not longer safe
  • Batteries with bare balance leads or bare leads are a short circuit risk. Short Circuit = FIRE. Fix or dispose of right away.
  • Batteries that have become too hot to touch are no longer safe

Even batteries that appear perfectly healthy can change at a moment's notice. It is important to monitor batteries while they are charging, and if possible use a LiPo bag to contain batteries as they charge.

NHRL has a number of battery disposal bins around the facility where you can surrender damaged LiPos safely.

If you do not feel safe handling a damaged battery, find a member of staff to assist you.

Fire and Flame-Based Weapons

Fire-based active weapons are allowed at NHRL, with the following stipulations...

  • Weapons which use fire or heat must be able to self light, and self extinguish.
  • They should also self extinguish in the event that the connection to the transmitter is lost.
  • A weapon is also considering self extinguishing if it flames out after 30 seconds from ignition
  • Competitors must demonstrate for safety the appropriate respect and precautions when working with flame or heat based weapons.

As of August 1 2021, bots at NHRL are limited in the mass of flammable gas that can be carried. Bots in the 3lb category are limited to 6 ounces of fuel. Bots in the 12lb and 30lb categories can carry up to 12 ounces of fuel.

Flammable Gas Container Regulations

If the amount of gas used on a bot is such that it can be fully depleted in less than 60 seconds of continuous firing, it is exempt from this section.

Large volumes Flammable gas on bots must be stored in a container that defaults to the closed position. Examples include;

  • "Lighter Filling" bottles where the nozzle must be depressed to release gas
  • Gas tanks that require an active pump or an inert gas to be pumped as a displacement.
  • Tanks with a spring-loaded nipple

In addition, these bottles cannot be implemented in a way that permanently depresses the opener. When the bot loses power or the bottle is severed from the rest of the bot, the canister must return to the closed position. This would include standard camp-stove style canister hoses.

Matches may be stopped and your bot disqualified if cage equipment, including cameras or safety gear, is being damaged by fire.

Rocket Motors

Rocket motors, also sometimes referred to as rocket engines, are growing more common as a weapon in combat robotics. There are special safety considerations that must be made while using rocket motors.

Total Impulse & Peak Thrust

The total impulse of all rocket motors on a robot cannot exceed 80 N*s, this includes rocket motors split across multiple bots in a multi-bot configuration.

The peak thrust of your motor(s) also should not be enough to lift the robot off the ground.


Rocket motors should be fully constrained in a tight tube or clamp that holds onto 50% or more of the outside surface area of the rocket motor. In addition, the back of the rocket motor should be retained, to reduce the risk of the motor coming out of the bot. If possible, design your robot in such a way that the rocket motor can be installed at the cage quickly, rather than needing to be installed in the pits and brought to the cage.

Deployment Charge

Most rocket motors available commercially include a deployment charge, which is a secondary small explosive charge that will expel hot gasses from the top of the motor a set amount of time after the motor itself has burned out. If possible, booster motors (with a delay of 0 or no deployment charge) should be used. If it is not possible to use a booster motor, the deployment charge should be removed from the motor.


Rocket motors are ignited using an electronically-initiated match, or e-match for short. These are also commonly referred to as igniters or initiators (although technically e-matches and initiators are different things, they serve a near-identical purpose in rocket motors). It is recommended not to use Estes e-matches, as they are more prone to misfires than other brands. MJG Firewire Initiators are recommended, as they generally have the lowest misfire rate. They are also the only commercial initiators that can be acquired without a license.

Igniters should not be installed in rocket motors until the bot is in the cage! Your electronics should be powered on before the igniter is put into the motor, in case there is an unexpected signal that triggers it on startup. Igniters must be inserted into the bot while the motor is facing into the cage.

Unloading & Misfires

If a bot has used its rocket motor more than 15 seconds before the end of a fight, it can be unloaded as a normal bot. If it has been less than 15 seconds, the cage manager may wait to ensure there is no secondary charge (such as a deployment charge or a smoke grain) still burning. After this time the bot can be unloaded as per normal.

If a bot has a rocket motor but does not fire it during the match, it is treated as a misfire. Misfires, also commonly referred to as hangfires, are when the signal is given to a rocket motor to fire, but for unknown reasons it does not. This may be due to a bad igniter, low power to the igniter, a wet motor grain, or a number of other reasons. The important thing is that the motor is still treated as live. At the conclusion of the fight, a hangfire bot must sit idle for at least 60 seconds after the match has concluded. Before being allowed to unload, the cage manager will cut the leads on the igniter and, if possible, remove the igniter from the motor. After this the bot must sit for at least another 60 seconds, after which it can be unloaded as per normal.

Destroyed Motors

If a bot has a rocket motor that is hit by the competitor's weapon and receives damage, it is treated as a hangfire (see above), unless it has been already fired. In addition to the hangfire response described above, the debris from a destroyed motor will require additional cleaning precautions. Any debris in the cage or on other bots should be removed with a soaking wet paper towel, which is then disposed of immediately.