Wednesday, October 29, 2003

Back From Modular Robotics Workshop

I just got back yesterday from Las Vegas where the IROS conference is happening. That's the "International Conference on Intelligent Robots and Systems". However, I showed up before it started and left the day it began. I attended a workshop that preceded the general conference organized by Mark Yim and his crew from the "smart matter" division at PARC.

Specifically, we got to learn how to use the Polybot modules, put them together to make certain forms and how to rapidly program them to do locomotion or other general movement. Basically, the polybots are individual modules with one degree of freedom. You can manually put these together by screwing them together and putting them into any configuration you want. After you have your desired form, you then use the software suite to program them to move.

One of the most impressive things was the record feature. Since every module adds 1 DOF to the system, and you typically use 10 or more modules to build arbitrary shapes, the system becomes very difficult to program and control! However, the record feature allows you to hold the robot in particular configurations, take a snapshot, then select the next configuration. You can then play back this series of configuration snapshots with a gradual transition between each one and create any type of locomotion you want. My colleague and I made a quadraped crawl with this feature in 10 minutes.

This workshop was a day-long event where we did a lot of exercises to practice using the system. There were a few breakdowns, of course, especially when systems are taken outside of the laboratory. In particular, the serial modules that communicate and power the Polybot arrays were frying for unknown reaons, so by the end of the day we were down to only 3 left. However, only a few individual modules malfunctioned which is an enormous accomplishment considering how notoriously difficult it is to maintain hundreds of robots and the amount of abuse we were visiting upon them with our wild and erratic locomotions.

There were two competitions during the day. The first was a race to see who could come up with the fastest locomotions. There were some very interesting attempts from people who have never had experience with modular robots. I believe the winner was a snake performing a sinusoidal gait with some passive components to keep it stable and give it better traction. My friend and I wanted to make a really ambitious configuration, so we tried to implement the rolling gait where you connect modules together in a circle. However, we quickly learned that there is too much calibration to be done to get it to work quickly and we only had 8 modules to work with whereas Yim did the rolling gait with 10.

Realizing this, we quickly reconfigured the modules to implement a lazy biped that uses his two feet to push himself and rests and slides on a pair of crutches. Unfortunately this didn't work out very well since we couldn't get effective forward motion. Finally, we decided on the quadraped which took about 20 minutes to assemble. We were late in finishing the design, but I think people thought we had the second-most ingenious design. The most innovative design was a robot doing somersaults that one of my other colleagues designed who was inspired by one of the locomotions he saw in Karl Sim's work.

The final competition, following the theme of Las Vegas, was to design a robot that would approach a slot machine, put a coin in the slot, pull the lever, and catch the coins that popped out with a cup. This was not an autonomous requirement since we could control the robot serially from a laptop. We split into two teams and spent about 3 hours working on the problem. In fact we went over our allotted time by an hour.

My team was fairly successful. We realized that these modules are really good at implementing caterpillar gaits, but the gaits by themselves are very unstable and incapable of changing direction. We decided to implement two caterpillars in parallel to each other, connect them together by a beam, and attach a robotic arm to the beam. The result was a crazy robot that was able to move around and turn in place using four snake appendages, and a robotic arm that was used to manipulate the slot machine. To my knowledge, no one has ever come up with a design quite like this. I'm quite proud of our innovative design and the fact that we were able to put the coin in the slot and push the lever. Sadly, we were unable to catch the coins since the time-to-response to move the cup in position was too short for successful teleoperation. I should know since I was the one at the controls!

The other team was not so successful. They tried to build a very long and large robotic arm and do recorded motion to interact with the slot machine. However, there were so many DOF (approx. 20) and the motor dead-reckoning was not accurate enough that the errors quickly added up and was unable to reach the correct positions. Implementing manual interface would be impractical in the amount of time allotted, so they reverted to a simpler design. However, the team began to disintegrate by this time, and they were unable to make a successful showing during their demonstration.

All in all, I really enjoyed this workshop. Mark has promised to send us all the videos he took of the workshop, so hopefully I should have some videos to link to that show our crazy snake monster. You'll be able to see our coin-slot operation in action with me at the controls

In the meantime, I encourage you to browse the videos of Polybot in action.

Also, comment on this story here over at Frontier Files.


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