Middleweight

The Middleweight class is for robots weighing up to 120 lb (54.4 kg) in the US, or 55 kg (about 121 lb) in the UK. Middleweights were a major class in the original BattleBots era, but as of 2026 they're one of the rarest classes to find an event for. Building one is closer to building a heavyweight than an insect: it takes a team, a real workshop, a vehicle to carry it, and an arena built for heavyweights.

Rules

SPARC: 120 lb (54.43 kg), called Middleweight in the SPARC Tournament Procedures.[1] Shufflers can weigh 150 lb, non-traditional drives 180 lb, and walkers 240 lb (see SPARC Robot Construction Specifications and Multibots, Walkers and Shufflers).[2]
UK (FRA): 55 kg. Event organisers may grant bonus weight, for example to walkers, at their discretion.[3]
BattleBots (historical): the Comedy Central-era middleweight limit grew from 115 lb to 120 lb by the final seasons. Today's BattleBots has a single 250 lb class.[4]
RoboGames lists a 120 lb / 54.5 kg combat class.[5]

Typical builds

Middleweights use the same kinds of parts as heavyweights, just smaller.

Frame: welded steel or aluminum tube, or thick machined aluminum plate. Plate parts are commonly cut by waterjet, laser or plasma, and SendCutSend cuts AR500 steel up to 0.500" thick.[6] Heavier sections usually need a local waterjet or plasma shop.
Armor and weapons: AR500/AR-type and other hardened steels, titanium, and tool-steel spinner bars and drums (see Armor and Materials). Weapon shafts, bearings and fasteners are sized like those on small industrial machinery (see Fasteners and Hardware).
Drive: large brushed DC motors or 63–80 mm brushless outrunners through chain, belt or gear reduction, often four-wheel drive (see Drive Systems and Speed Reduction).
ESCs: VESC-based controllers such as the Flipsky 75200 (14–84 V) are popular for brushless setups, and large brushed controllers for brushed ones.[7]
Batteries: large LiPo or LiFePO4 packs. Above 48 V nominal, SPARC events need to approve the system, and FRA rules cap DC voltage at 75 V unless the organiser approves more.[8][9]
Arena: SPARC's arena guide treats everything above 30 lb as welded-steel territory. For events up to 220 lb it suggests walls of 1.5" polycarbonate equivalent and a floor of at least 40 × 40 ft, and says such arenas cost $100,000 or more.[10]

What it costs

As of October 2026, BattleKits lists its assembled Middle Weight Kit drive platform at $1,340 without motors. Its motor options run from $238 for a pair of E30-400s to $2,276 for four A28-400s. With two A28-400 motors, batteries and an AmpFlow controller, the platform weighs about 62 lb, which shows how much of a 120 lb budget the drive alone can take.[11][12] Brushless parts are cheaper per watt: Flipsky lists the 75200 ESC from $120 and its 63100 motor at $137–143.[13][14] Once you add steel, a weapon, batteries, spares and travel, expect the total to run into many thousands of dollars.

Safety requirements

Overview only. Always read the current rules of the event you're entering, and see Safety, Failsafes and LiPo Battery Safety.

Shutdown: SPARC requires a mechanical main disconnect (a switch such as a Hella or Whyachi, or a removable link) that can be operated within 15 seconds without reaching into a weapon's path. Full deactivation must take under 60 seconds, and a power light must be visible.[15] FRA rules require a tool-free, insulated removable link instead of a key or switch.[16] See Switches.
Failsafes: drive and weapon must stop on signal loss, low receiver voltage or power loss. FRA rules also restrict which radio bands are allowed for each class; 2.4 GHz spread-spectrum is allowed in every class.[17] See Radios.
Pneumatics and hydraulics: SPARC's exemptions stop at 12 lb, so a middleweight must meet every rule on rated components, relief and dump valves, and fill fittings.[18] Under FRA rules, hydraulic accumulators are banned and hydraulic systems need a test point.[19] These systems are well beyond this wiki's scope. Get an experienced mentor before attempting one.
Spinners: FRA rules require advance approval for spinning weapons over 500 RPM, over 500 mm across, or heavier than 10% of the robot, and every spinner must stop within 60 seconds.[20] See Spinner Design.
Pits and handling: locking bars, mechanically fastened edge covers, and stands that lift the wheels off the floor are standard. Pull the main link before anyone works on the robot.
Insurance and venues: few venues and insurers are set up for robots this size. Organisers need liability cover that names robot combat (see Running an Event).

Getting started

Experience first: build and fight smaller robots, ideally a Featherweight or Lightweight, before tackling 120 lb.
Crew roles: a typical team has a driver, a weapons and electrical lead, a mechanical lead who does repairs between fights (see Repairs Between Matches), and someone handling batteries, spares and paperwork. Moving and lifting a middleweight takes two or more people.
Shop space: you'll need a garage or makerspace with welding, cutting and drilling tools that can handle thick steel (see Hand Tools and Basic Machining), plus a safe enclosure or large outdoor area for driving tests. Never spin up a weapon in the open.
Transport: plan for a pickup, van or trailer, plus a heavy-duty dolly or cart, ramps or a lift, ratchet straps, and approved battery containers.
Confirm the class: contact organisers before building. A 120 lb class only runs if enough robots enter, so ask what happens if too few register.

Where they fight

As of October 2026:

RoboGames lists a 120 lb class. Its most recent world championship was its 20th, held April 18–21 in San Jose, and the next event is listed as "to be announced".[21][22]
RobotCombatEvents.com shows very few 120 lb listings in recent years, mainly RoboGames 2023–2024 and Brendan's Bash in Victoria, Australia (2022).
NHRL runs only 3, 12 and 30 lb classes.[23]
In the UK, the FRA rules define a 55 kg class; ask the FRA-listed event organisers about middleweight fights.[24]

See Events and Major Competitions.

Notable robots

The best-documented middleweights fought in the original BattleBots. Wikipedia's results table lists these champions:[25]

Season	Middleweight champion
BattleBots 1.0 (2000)	Hazard
BattleBots 2.0 (2000–2001)	Spaz
BattleBots 3.0 (2001)	Hazard
BattleBots 4.0 (2002)	Hazard
BattleBots 5.0 (2002)	T-Minus

Blade Runner – a Comedy Central-era middleweight and the first robot to attempt meltybrain drive, though the technology never worked as planned (see Melty Brain).[26]
Chiabot – a middleweight entered in all five Comedy Central seasons by SimCity creator Will Wright.[27]

See Robot Combat History and TV for more history.

Middleweight

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