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DARPA Subterranean Challenge: Urban Circuit Preview

The second event in the DARPA Subterranean Challenge starts this week

6 min read
Darpa SubT Urban Circuit
Image: DARPA

The Urban Circuit of the DARPA Subterranean Challenge is the second of four robotics competitions that send teams of state-of-the-art robots into challenging underground environments in an attempt to seek out artifacts while creating detailed maps. Last August, the robots explored a man-made tunnel system in the NIOSH research mine near Pittsburgh, Pennsylvania. And starting this Thursday, the teams will be taking on the urban underground, at Satsop Business Park in Elma, Wash.

If you’re not familiar with the DARPA Subterranean Challenge, here’s an overview video from DARPA to get you caught up on the whole thing:

This post will be focused on a preview of the Urban Circuit, but if you’d like to learn more about SubT we’ve got plenty more coverage on the challenge itself, the teams that are involved, and the results of the first competition, the Tunnel Circuit.

The overall objective of the SubT Challenge is for each team of robots to spend 60 minutes exploring an underground (or simulated underground) course, searching for a variety of artifacts. You can read more about how the scoring works here, but the team of robots that’s able to find the most artifacts (and report back their exact location) in the least amount of time wins.

DARPA’s intention is that the Urban Circuit “will represent human-made urban environments such as municipal infrastructure and mass transit.” We’d sort of figured that they’d choose a subway station, mostly because they’ve been using subway station graphics on the SubT website. But DARPA has chosen Satsop Business Park (just to the west of Olympia, Wash.) as the location for the event, and it’s much more of an industrial-y looking place. Here’s an environment preview video:

Environments like these can be pretty grim for autonomous robots. There’s all kinds of stuff on the floor, lots of localization-unfriendly flat surfaces, dirt, water, stairs, ledges—it sucks if you’re a robot (or roboticist). But that’s the point, because the SubT challenge is DARPA-hard. That’s what the teams and their robots are preparing for, and I can’t imagine they’d want it any other way.

Something in particular to look out for in the Urban Circuit is verticality: Things like stairs, ladders, ledges, and holes in the ground and ceiling that need to be explored or traversed. The Tunnel Circuit didn’t really have that; there may have been one or two optional holes, but nothing that robots were required to deal with in order to make progress. We’re expecting that verticality will be a much more significant (i.e. mandatory) part of the Urban Circuit, which will definitely add some risk. And some drama!

The SubT challenge is DARPA-hard. That's what the teams and their robots are preparing for, and I can't imagine they'd want it any other way

A key thing to remember is that all teams are allowed to do is push their robots through the entry to the Urban Circuit course, and after that, they can’t touch them. Once the robots move out of communications range, they’re completely on their own, operating fully autonomously without any human input at all.

During the Tunnel Circuit, teams tried a variety of very creative ways to keep in touch with their robots, both to give them high-level instructions and to get back artifact coordinates to score points. We’re expecting even more autonomy for the Urban Circuit, as teams have refined their communications strategies over the past six months.

New to the Urban Circuit are two different artifacts: gas, and vent. They replace the drill and fire extinguisher artifacts from the Tunnel Circuit. Here’s what we know about the new artifacts:

The gas artifact is a CO2-emitting device used to simulate a range of hazardous air quality conditions, such as a gas leak, poor ventilation, or fumes and smoke. Finding this artifact represents identifying areas that would be hazardous for personnel, including areas where breathing apparatus may be necessary.

The vent artifact is a typical supply register commonly found in homes or work environments. Finding this artifact represents identifying potential areas with fresh air or an escape route to the surface.

SubTImage: DARPA

The vent artifact can be found on a wall or ceiling at any height, and it’ll be heated to at least 30 °C above ambient temperature. The gas artifact is a little trickier; the gas itself will be kept at 2000 ppm in a room with an open door. There won’t be any visual indicators; robots will have to sense the gas, and precisely identify the room that it’s coming from by finding the center point of the entry door threshold (at floor level) of the room where the gas is detected.

Besides the new course and new artifacts, DARPA has made some updates to the SubT rules for the Urban Circuit. We’ve gone through and highlighted some of the most relevant ones:

The scale and complexity of competition courses is expected to vary across events and may vary from run to run due to configuration changes. The design of the Urban Circuit course is intended to assess the ability of teams to address challenging urban environments that include multiple levels, degraded terrain, and austere environmental conditions.

Each of the two courses are expected to include multiple levels, requiring teams to traverse stairs, ramps, or vertical shafts to access the entire competition course. Stairs are expected to be a challenge element on both courses. The height difference between levels requires teams to traverse multiple flights of stairs to reach a different level.

Did we mention that the Urban Circuit will include multiple levels? Because there are going to be multiple levels. 

Vertical shafts and openings vary by course but may be as large as 2.5 m x 2.5 m. Each level may also include mezzanine levels. Artifacts may be located on mezzanine levels and in some cases may require elevated vantage points for line-of-site detection. It is expected that some areas could include significant drop-offs. Other areas include curbs that typically range from 0.1 to 0.2 meters high.

Interesting that there will be some artifacts that robots will have to spot without necessarily being able to get particularly close to them. And while curbs are good, the “significant drop-offs” is a bit worrisome. 

The width of passages at the Urban Circuit site vary greatly and include large open areas as well as narrow constrained passages common in urban environments (i.e., doorways). It is expected that some portions of the course will only be accessible via passages that are approximately one meter in height and/or one meter in width. For the Urban Circuit, it is expected that up to 50 percent of the competition course could be inaccessible for systems that cannot traverse these passages.

While a majority of passages at the Urban Circuit site are greater than 1 m x 1 m, some passages are as narrow as 0.8 meters and a limited number of passages are as narrow as 0.7 meters. Some artifacts (up to 10 percent) may be inaccessible without traversing the more constrained passages. 

Chubby robots are on notice!

Dispute Cards are intended to provide teams a mechanism to submit a formal dispute or request for review by the Chief Official. The Dispute Card must be completed and delivered by the Team Lead to the relevant Course Official, Team Garage Coordinator, or Chief Official. The Dispute Card must be submitted within 30 minutes of the completion of the run in question. All submissions will be reviewed by the Chief Official in a timely manner. All decisions made by the Chief Official are final.

This is a new mechanism for the Urban Circuit. We don’t know whether there was some specific incident that prompted this, or whether DARPA simply decided that it would be a good system to have in place. 

In the event that multiple teams have an identical score, tiebreakers will be applied in the following order until the tie is broken:
- Earliest time that the last artifact was successfully reported, averaged across the team’s best runs on each course
- Earliest time that the first artifact was successfully reported, averaged across the team’s best runs on each course
- Furthest distance traveled by any deployed system 

That last one (furthest distance traveled by any deployed system) is a new addition. I’d be surprised if a tiebreaker made it that far, but it does emphasize DARPA’s interest in exploration.

Teams are encouraged to provide audible and visual recovery aids such as flashing LEDs and audible cues to help Competition Staff locate deployed systems or components.

Many robots drop things like wireless repeaters as they progress through the course—DARPA was explicit that teams should not necessarily expect them all to be returned, but the agency may have gotten a little bit fed up attempting to track down all the robot droppings after every run.

There are currently no restrictions on the use of tethers for power, communications, or physical retrieval. However, teams are encouraged to consider the significant limitations imposed by the large-scale, potentially dynamic, and complex environments of interest.

This is more of a reiteration from DARPA than a new rule, but it’s worth noting that it’s being emphasized again for the Urban Circuit. Several teams who did use tethers for the Tunnel Circuit seemed to derive a significant advantage from them, and perhaps DARPA is concerned that more teams will use that approach. Which, of course, they can, it’s just that tethers can also be very limiting, and it seems like DARPA would really like to see more versatile, creative solutions.

Since the Urban Circuit is a closed course, the best way to follow along with the event will be through DARPA’s livestream, which will be on a one hour time delay (boo!) but may also have commentary this time around (yay!). Also, you can hear directly from the teams themselves by following #SubTChallenge on Twitter

Scored runs (the thing that’ll be the most fun to watch) will take place February 20 (Thursday) to February 22 (Saturday), and also February 24 (Monday) to February 26 (Wednesday). There’s a media day on the 24 that we’ll be at, so make sure and let us know if there are specific things you want us to check out.

[ DARPA Subterranean Challenge ]

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