Rats, Doom and a Very Tiny VR Rig
Back in 2021 a quirky experiment caught the attention of PC gamers everywhere. Researchers taught two rats named Carmack and Romero to “play” a simplified version of Doom by running on a ball for sugar water rewards. It was funny, a bit surreal and raised a serious question. Were the rats actually playing Doom or just running in response to basic stimuli?
The project’s creator, Viktor Tóth, was not fully satisfied with that first attempt. The original setup only let the rats move through a corridor toward an enemy. There was no real way for them to control shooting, and the visual immersion was limited. You could argue they were kind of playing Doom, but it was a stretch.
Four years later the team is back with a much more advanced system. The new setup dramatically upgrades the display, the motion tracking and most importantly it gives the rats a proper trigger to fire a weapon inside the game. This time the hardware looks a lot closer to a very tiny custom VR rig built just for rodents.
How the Rat Doom Rig Actually Works
The basic idea is the same as before. The rat’s real world movements are mapped into a virtual Doom environment. Everything that matters is handled by external hardware. Sensors track how the rat moves, the system renders what the rat “sees” and the rat gets a reward when it does the right thing.
In the original version the rat was suspended in a harness above a ball. As it ran, the ball rotated. Motion was translated into movement down a Doom style corridor with an imp at the end. When the rat moved correctly it received sweetened water. That worked, but there were clear limitations in both control and immersion.
The new version significantly upgrades the experience.
- Wraparound AMOLED display The rat now views the game world on a curved AMOLED screen that wraps around more of its field of view. This increases immersion while intentionally leaving space for whiskers to move freely, which is important for how rats sense their surroundings.
- Physical feedback for collisions When the rat runs into walls in the game, the system puffs small bursts of air onto the rat’s snout. That gives instant physical feedback that corresponds to the virtual environment, a clever way to make the digital world feel more real.
- Motion and sensors all external As before, the entire system uses external sensors and motion tracking rather than invasive methods. The rat simply moves and interacts with the custom hardware around it.
The biggest change is the new shooting input. Instead of some indirect cue, the rat can now fire a gun in Doom using a dedicated trigger mechanism.
Tóth describes the shooting input as a custom built hand operated lever that the rats pull with their paws. The lever is held in place by small springs and housed in a 3D printed casing. Inside the mechanism there is a rotary encoder to read motion and a stepper motor to actuate the lever. In hardware terms this is a neat little hybrid of mechanical design and precise input tracking, very similar in spirit to an ultra specialized controller.
This new control scheme finally gives the rats two meaningful inputs in the game world. They can navigate through the map and they can decide when to fire. From a gamer’s point of view that makes the activity look a lot closer to actual play, even if it is still driven by rewards and training.
Training Tiny Doom Marines
The second generation project is a collaboration between Viktor Tóth and electrical engineer Sándor Makra, with Akos Blaschek helping document everything. One of the more interesting touches is that they are open sourcing the entire setup. On the project’s website there is a detailed hardware guide that explains how to build your own rodent VR rig, from the motion system to the trigger mechanism.
In terms of results the team reports that the rats successfully learned to navigate through the virtual environment and use the shooting lever. Habituation took around two weeks per rat. That is just the time needed for the animals to get comfortable with the hardware and basic interaction. Advanced training did not get as far as the team would have liked because of time limits, but the early data suggests strong engagement with the system.
To properly validate the behavior and prove exactly how the rats understand the game would require longer training. For now we can say that they definitely move through a Doom level and they definitely trigger the weapon using their paws to pull a lever. Compared with the first project, the new setup is a clear step up in both immersion and control.
The original rats Carmack and Romero are no longer around, but their legacy as the first rodent Doom pioneers continues in this upgraded experiment. What began as a fun side project has evolved into an impressive mix of VR research, hardware hacking and game culture. For PC and Doom fans it is a charming reminder of how far interactive tech has come. We now live in a world where even rats can run and gun in Doom on a wraparound AMOLED display and a custom 3D printed controller.
Original article and image: https://www.pcgamer.com/games/fps/the-doom-playing-rats-are-back-and-now-theyve-learned-how-to-shoot/
