# Self-righting mechanism

In robot combat, a self-righting mechanism or srimech (sometimes spelled as srimec or shrimech) is a device used to re-right a robot should it get flipped. Biohazard of BattleBots was the first robot to self-right.

## Military applications

As of 2016, the U.S. Army Research Laboratory (ARL), based at Aberdeen Proving Grounds, MD, developed self-righting robots for bomb defusal and reconnaissance. Listed as a 2004–2020 effort, the prototype was called CRAM, for compressible robot with articulated mechanisms. ARL scientists were led by Chad Kessens, and collaborated with researchers from the University of California, Berkeley, and Johns Hopkins University to develop a prototype.
Cockroach exoskeletons inspired researchers to manufacture a robot that can move around rapidly in both open and confined spaces with self-righting capabilities.
In 2016, ARL and its collaborators published additional research, "Cockroach-inspired winged robot reveals principles of ground-based dynamic self-righting", demonstrating a bio-inspired design. Researchers showed that robots can use insect body structures to achieve self-righting, as demonstrated in the rounded shell and mobile wings of the robot prototype.

## American Robot Wars: 1994–1997

Biohazard was the first robot to self-right in combat, against Vlad the Impaler in the 1996 tournament, however since the match had ended it made no difference to who actually won. Terminal Frenzy had attempted to right itself when it earlier came up against Biohazard, but failed to do so. The next year Vlad the Impaler fought Biohazard again, and the former used its special pneumatic lifting arm to self-right numerous times, yet it still lost the judge's decision.

## UK Robot Wars Series 2-3

The first attempted self-right in the UK Robot Wars was by a robot called Chaos, during its Series 2 heat final. However, it was unable to do so. Later in the series, Cassius successfully righted itself with its pneumatic flipping arm, after Sir Killalot had flipped it over with his drill during the semi-final pinball trial. Cassius was flipped again in the Grand Final, but it self-righted and flipped Roadblock to win the eliminator. In Series 3, Chaos' successor Chaos 2 used its innovative rear-hinged flipper panel to catapult itself through the air and then land on its wheels, a technique that later became standard.

## Weapon srimechs

The majority of flippers can double as srimechs. However, most flippers are powered by CO$_2$ and therefore have limited uses. Some axes can also be used as srimechs; the first robot to successfully use an axe to self-right was Iron Awe in Robot Wars Series 4.

### List of robots with weapon srimechs

Robots are listed alphabetically. The weapon indicated is the weapon used to self-right.
| Robot's name | Competing series | Weapon | Notes |
| Apollo | Series 8–10 | Flipper | |
| Axe-Awe | Series 5, Extreme 1 | Axe | |
| Barbaric Response | Series 6–7, Extreme 2 | Flipper | |
| Beast | Series 5–8 | Flipper | |
| Behemoth | Series 2–9, Extreme 1–2 | Lifting Scoop | |
| Bigger Brother | Series 4–7, Extreme 1–2 | Flipper | |
| Bonk | Series 8 | Hammer | |
| Bulldog Breed | Series 4–7, Extreme 1–2 | Flipper | |
| Cassius | Series 2–3 | Flipper | First robot to successfully self-right in UK Robot Wars |
| Chaos 2 | Series 3–6, Extreme 1–2 | Flipper | First rear-hinged flipper to catapult the robot back onto its wheels |
| Dantomkia | Series 6–8, Extreme 2 | Flipper | |
| Dominator 2 | Series 4–6, Extreme 1–2 | Axe | |
| Eruption | Series 8–9 | Flipper | |
| Firestorm | Series 3–7, Extreme 1–2 | Flipper | |
| Gravity | Series 7, Dutch Series | Flipper | |
| Hydra | Series 5–7, Extreme 2 | Axe, Flipper | |
| Iron Awe | Series 4 | Axe | First robot to successfully self-right with an axe |
| Judge Shred 2 1/2, 3 | Series 6–7, Extreme 2 | Flipper |
| Killerhurtz | Series 2–4 | Axe | |
| Lightning | Series 7, Extreme 2 | Flipper | Flipper was side-hinged |
| Meggamouse | Series 9 | Flipper | |
| Mortis | Series 1-4 | Lifting Arm, Axe | |
| Mute | Series 7, Extreme 2 | Flipper | |
| Ripper | Series 7 | Flipper | |
| Roobarb | Series 6-7 | Flipper | |
| Storm II | Series 7–8, Extreme 2 | Lifting Arm | |
| Terrorhurtz | Series 5–9, Extreme 2 | Axe | |
| Thermidor II | Series 4–8, Extreme 1-2 | Flipper |
| Thor | Series 6–9, Extreme 2 | Axe | |
| Tsunami | Series 7, German Series | Flipper | |
| T-Minus | Seasons 3.0–5.0 | Flipper | |
| The Matador | Seasons 4.0–5.0 | Flipper | |
| Toro | Seasons 2.0–5.0 | Flipper | |
| Bronco | ABC Seasons 1–2 | Flipper | |
| The Judge | Seasons 3.0–5.0 | Axe | |
| frenZy | Long Beach 1999, Las Vegas 1999, Seasons 1.0–5.0 | Axe | |
| Chomp | ABC Seasons 1–2 | Axe | |
| SlamJob | Seasons 3.0–5.0 | Axe | |

## Other methods of self-righting

Some robots had weapons that couldn't be used for self-righting, and so incorporated separate dedicated srimechs. These varied in design and effectiveness; examples include Razer's side wings, Hypno-Disc's srimech bar and Panic Attack's top lid. These did not detract from the weapon, but could easily break if damaged repeatedly, and also took up some of the robot's precious weight allowance - Razer, after the addition of its wings, had to have over 450 holes drilled into it to keep it within the 79.4 kg (175 lb) weight limit.

### Body shape

A rarer and more difficult type of srimech was to design the robot's body in such a way that it could roll back onto its wheels when flipped. Sometimes known as a "rollover" design, robots with this ability included Mega Morg. While a fairly ingenious solution, that did not require any additional power or mechanics, there were still flaws. It was extremely difficult to get the design perfect, and if flipped without enough momentum or flipped from the front or back, the robot would be left stranded. Mega Morg's predecessor, The Morgue, was also defeated in Series 4 by Firestorm when it was flipped against the arena wall, preventing it from rolling over.
Some robots were not true rollover designs, but had other design elements intended to aid them in self-righting. Examples include the rounded Lexan panels on the rear of Behemoth, without which it would have stranded itself on its back when self-righting, and Spikasaurus' roll-bars. These were often effective but, like active srimechs, they were vulnerable to damage.