RobotRobot: New weight-class page: Middleweight

2026-10-17T23:23:38Z

New weight-class page: Middleweight

New page

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.

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==Rules==
* '''SPARC''': 120 lb (54.43 kg), called Middleweight in the '''[[SPARC Tournament Procedures]]'''.[https://sparc.tools/SPARC%20Tournament%20Procedures%20v1.2.pdf] Shufflers can weigh 150 lb, non-traditional drives 180 lb, and walkers 240 lb (see '''[[SPARC Robot Construction Specifications]]''' and '''[[Multibots, Walkers and Shufflers]]''').[https://sparc.tools/SPARC_Robot_Construction_Specifications_v1.7.pdf]
* '''UK (FRA)''': 55 kg. Event organisers may grant bonus weight, for example to walkers, at their discretion.[http://www.fightingrobots.co.uk/documents/Build-Rules.pdf]
* '''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.[https://en.wikipedia.org/wiki/BattleBots]
* '''RoboGames''' lists a 120 lb / 54.5 kg combat class.[http://robogames.net/events.php]

==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 '''[[Fabrication Services|waterjet, laser or plasma]]''', and SendCutSend cuts AR500 steel up to 0.500" thick.[https://sendcutsend.com/materials/ar500/] 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.[https://flipsky.net/products/flipsky-75200-84v-high-current-with-aluminum-pcb-based-on-vesc-for-fighting-robot-surfboard-agv-robot]
* '''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.[https://sparc.tools/SPARC_Robot_Construction_Specifications_v1.7.pdf][http://www.fightingrobots.co.uk/documents/Build-Rules.pdf]
* '''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.[https://sparc.tools/SPARC_Arena_Construction_Best_Practices_v1.1.pdf]

===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.[https://battlekits.com/order/][https://battlekits.com/] Brushless parts are cheaper per watt: Flipsky lists the 75200 ESC from $120 and its 63100 motor at $137–143.[https://flipsky.net/products/flipsky-75200-84v-high-current-with-aluminum-pcb-based-on-vesc-for-fighting-robot-surfboard-agv-robot][https://flipsky.net/products/flipsky-sensored-outrunner-brushless-dc-motor-battle-hardened-63100-140kv-170kv-190kv-5500w] 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.[https://sparc.tools/SPARC_Robot_Construction_Specifications_v1.7.pdf] FRA rules require a tool-free, insulated removable link instead of a key or switch.[http://www.fightingrobots.co.uk/documents/Build-Rules.pdf] 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.[http://www.fightingrobots.co.uk/documents/Build-Rules.pdf] 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.[https://sparc.tools/SPARC_Robot_Construction_Specifications_v1.7.pdf] Under FRA rules, hydraulic accumulators are banned and hydraulic systems need a test point.[http://www.fightingrobots.co.uk/documents/Build-Rules.pdf] 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.[http://www.fightingrobots.co.uk/documents/Build-Rules.pdf] 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".[http://robogames.net/index.php][http://robogames.net/events.php]
* '''[https://www.robotcombatevents.com/searches?search%5Bcategory%5D=event&search%5Bterms%5D=&search%5Btype_id%5D=2 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.[https://wiki.nhrl.io/wiki/index.php?title=NHRL_Rules]
* In the '''UK''', the FRA rules define a 55 kg class; ask the FRA-listed event organisers about middleweight fights.[http://www.fightingrobots.co.uk/documents/Build-Rules.pdf]

See '''[[Events]]''' and '''[[Major Competitions]]'''.

==Notable robots==
The best-documented middleweights fought in the original BattleBots. Wikipedia's results table lists these champions:[https://en.wikipedia.org/wiki/BattleBots]
{| class="wikitable"
! 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]]''').[https://en.wikipedia.org/wiki/Translational_drift]
* '''Chiabot''' – a middleweight entered in all five Comedy Central seasons by SimCity creator Will Wright.[https://en.wikipedia.org/wiki/BattleBots]

See '''[[Robot Combat History and TV]]''' for more history.

==See also==
* '''[[Lightweight]]''' (60 lb) and '''[[Heavyweight]]''' (250 lb)
* '''[[Featherweight]]''' (30 lb)
* '''[[RobotClasses|Robot Classes]]'''
* '''[[Armor and Materials]]''', '''[[VESC]]''', '''[[Switches]]'''
* '''[[Safety]]''' and '''[[Failsafes]]'''

Middleweight - Revision history

RobotRobot: New weight-class page: Middleweight