In this second part of the All Japan Robot Sumo Tournament interview series we explore some of the technical background behind the sumo robots and the strategies and tactics used by some of the top Japanese competitors. In addition to patiently answering all of our endless questions, the officials provided us with video clips from the 2005 competitions (see video below) that clearly, and dramatically, illustrate many of the topics they touched upon.
Note: Participants from the All Japan Robot Sumo Tournament office included Takeshi Kanai (Secretary General), Masaru Ishikawa (Vice Secretary General - Chief Judges), and Akiko Tsuda (Public Relations Section).
Before we get into the extensive Q&A section of this article, it might be useful to watch the following video clip. The video includes some of the top competitors from the 2005 competition (3 kg. classification), and we think you'll be as suprised as we were by some of the action and tactics.
Lem: You mentioned before that roughly half the robot entries are autonomous and half are radio controlled (R/C). The sumo action seems so fast. How can an operator possibly control the robot that quickly?
Kanai: Each team designs their own entry, so their strategies vary quite a bit. Of course, the autonomous robots have sensors to track their opponents and also the edges of the ring. Some of them have as many as five sensors and can track their opponents even when they manage to get behind them.
Although the R/C entries are basically remote controlled by their operators, there's no rule to prohibit the use of sensors and autonomous behavior as well. As a result, some of the top robots use R/C for general positioning and movement, then the operator will hit a button that locks the robot on target to attack using its sensors and autonomous control program. It's just like the fighter jet pilots do in the Top Gun movie.
Lem: We saw in the video clips that some of the robots seem to feint or draw back slightly then attack. Is that what's really going on?
Kanai: Yes, that's exactly right. The teams give a lot of thought to the behavior they can expect from the other entries. Many times you can see their robots pull back when the match starts then quickly move out of the way as the other robot attacks. If their timing is right they can get behind their attacker and push it out of the ring. When you have two robots fighting that use similar strategies it sometimes resembles an unbelievably complex and lightening fast dance.
Lem: Most people think robot sumo is a game of pure strength and pushing power.
Ishikawa: There are many entries every year that focus on that aspect, and they usually do very well. Other teams try to emphasize quick movement, or special tactics to gain the advantage. In many ways, this is real sumo. You see all the same positioning, leverage, and strategy in action. It's definitely just as exciting as real sumo.
Lem: Some of them even seem to fly in the air.
Kanai: That's a deliberate part of the design approach for those particular teams. Most sumo robots are designed for head to head pushing battles, so they are often very vunerable from the rear. To get behind your competitor you either have to be very fast and go around them, or you can jump over the top. After all, your competitor comes equipped with a very useful ramp.
Lem: In some of the matches the two robots seem to be almost identical, yet one of them quickly gains the advantage. What are some of the design factors involved?
Kanai: Even with the same overall dimensions, motors, and weight the teams have found ways to improve performance. For example, some of them will try to move the robot's center of gravity further to the front to give it the ability to turn faster in competition. It's a real advantage against a robot that has its weight and mass more evenly distributed. Of course, all of the design factors have to work together to achieve the team's strategy.
They have also become very resourceful and creative with material selection. A good example is the wheels/tires used by the robots. They discovered that hose manufacturers are an excellent source. Hose companies have to provide products that have a wide range of characteristics, that work well in many different regions of the country and the world, and under widely varying temperature and environmental conditions. It gives the teams a great source of materials to chose from.
Lem: What other challenges do they face because of the high speed and sudden impacts involved? In many ways it reminds me of cars crashing on the highway.
Kanai: That's a good comparison. Although we haven't measured the actual shock and G forces involved, they must be very similar. The teams have to learn good design practices, and take a lot of care. We have occasionally had some robots catch fire when their batteries became loose started moving around generating a lot of friction and heat inside the robot chassis. We always have trained staff and fire extinquishing equipment ready, but it can be very embarassing for the team involved.
The high speeds also create some interesting sensing and tracking challenges. It's not enough for a robot to sense were it's opponent happens to be. In the high speed matches it also has to take the direction and velocity of the opponent into consideration so that it can attack where the other robot 'will be' instead of where 'it is.'
In the next article in this series, we'll explore another unique competition staged annually by the same organization here in Japan: Robot American Football. Yes, we said "American Football", real American football, not soccer, played by teams of robots, with lots of action and even cheerleaders.
Photo credit: All Japan Robot-SUMO Tournament Office (all screen shot images and the original video footage used for this article.)
FSI-All Japan Robot Sumo Tournament Website (Japanese)