The challenges of designing a firefighting robot.
"It seemed like killing two birds with one stone," says John Seminatore, graduate researcher at theTREC lab and DRC program manager. Over the past year the lab has continued work on both robots, learning from several design flaws that arose during SAFFiR's testing to build ESCHER the DRC.
"We realized that we were woefully underpowered in computing power," says Seminatore.To rectify this issue in SAFFiR, the team enhanced ESCHER to feature the equivalent computing power of two desktop and two laptop computers. However, adding the extra computers added a huge amount of power draw, which meant more batteries, and more weight. "This overwhelmed the weight capacity of the knee," says Seminatore, so the team doubled up the power going into the knee and switched out the physical mechanism that powered it, which was originally a Hoeckens linkage.
"[The Hoeckens linkage] gave us nice linear power curves through the entire range of motion," explains Seminatore. "It turned out it's a great mechanism but it's not really what you want in a knee." ESCHER now features a more traditional design that is just a lever arm with two actuators attached to it.
Most of ESCHER uses aircraft grade aluminum, with many of the parts designed in-house, including the actuators and the circuit boards that power the robot. "We have a very good machine shop and some very talented engineers and machinists on the team who are students," says Seminatore. Every part on the robot was at one point manufactured by the students, which is rare. "Not a lot of labs build their own stuff, but it's pretty vital to what we are doing," he adds.
This need became apparent during testing, as the team was getting bad readings off of the knee's encoders. "We pulled one and we felt it, and all the bearings had been destroyed," says Seminatore. As it turned out, the shaft that the encoders were attached to weren't perfectly concentric, so it destroyed all the bearings in the encoder.
The team redesigned the part and manufactured it in the lab, replacing all 16 encoders on the robot within a week. If they needed help from an outside shop, the robot would have been down for eight weeks. With in-house capabilities, the robot was up and running three days after the new encoders were installed.
The lab has even started to use 3D printers, making parts for protective purposes--not anything load bearing or structural.
"We are a lab that prides itself on getting our hands dirty," Seminatore says.
Whole Body Control
The biggest engineering challenge has been bringing all the disparate teams together. "A small change on what the software team needs in terms of computing power can ripple through the entire mechanical design," says Seminatore.
Another challenge has been using parts in ways that have never been done before. For example, the main motor is a series elastic actuator, the same type of motors that are used in modern prosthetics, which have never really been applied to a full sized humanoid robot.
The robot's actuators were also custom made. According to Seminatore, what makes them clever is that they are not rigidly attached to the robot; instead, they are attached via titanium springs for shock absorption.
"It functions like your tendons," he adds. "Your muscles aren't directly connected to the bone, you've got the springiness of the tendon that helps store energy and make walking much more efficient."
Traditionally, robots are controlled via position control. You command a joint to go to a certain angle and then you play that over and over. In ESCHER, load cells are incorporated into each of the motors which measure the force placed on each of the joints. This gives the robot a basic sense of touch as it walks. It reaches its foot out, slowly puts weight on it, making sure there is a stable plant, then moves the next foot.
Additionally, the robot features a custom whole-body controller which gives the robot center of mass awareness.
"If I shove the robot and that center of mass moves, the robot can calculate how much force it takes to move its center of mass back into position because we can calculate all the forces going through each of the joints," adds Seminatore.
If the robot were to be shoved from behind, the robot moves forward, drops its hips, flares its arms back and then stands up, much like human nature.
Developing that center of mass was a difficult task. In fact, the TREC lab may be the second or third group in the world to get this capability working on a robot. "We were right there in the running with those who did it for the first time," he adds. "Normally you focus on controlling a specific joint, we're focusing on what the whole body is doing when a joint moves"
A SAFFiR Robot
All of the work the team has done in preparation for the DRC will helpTREC in their SAFFiR project for the Navy, as the ESCHER platform will eventually replace the current SAFFiR robot. The next challenge, apart from the DRC, will be to improve mobility on a ship.
"One of the big problems a lot of the DARPA robots have is that they are big," explains Seminatore. "We are on the smaller side compared to a lot of the other robots, and that's by design. "This design is necessary as the SAFFiR robot will have to fit into much smaller, much more confined spaces of a ship, and handle a moving floor with no outside frame of reference. The robot will also have to work around people.
"The firefighter or sailor that is operating near the robot has to be able to shove the robot out of the way to get past it and not be afraid to be in a very confined space with it," says Seminatore. An all-electric robot, ESCHER is safer to operate around than its hydraulic counterparts.
However, there are still a huge amount of challenges to overcome before the robot is "grunt proof." Right now, it takes a team of PHDs to operate ESCHER. It still needs to be simplified down to something more robust, durable, and easier to interact with.
"You don't want a massive computing station and a command center operating a single robot," says Seminatore. "Even a joystick is probably a little too much," he adds.
Other challenges pertain to actions generally taken for granted. For example, picking up a cup from a table. "When I reach out and I try to pick up the cup, I know if there is water in the cup. I shouldn't turn it upside down," says Seminatore. "I know the best way to approach the cup." The robot has no idea; it doesn't even know that the cup isn't attached to the table.
Today, the best algorithms can only identify objects with a 60% accuracy using supercomputers, but a robot can't carry that much computing power on board.
In addition to knowing the object, the robot must also know its condition. "How does the robot know that the cup can't be picked up from the top because it needs access to what's inside of it," asks Seminatore.
These are enormous artificial intelligence challenges, and while the TREC lab has been working to overcome them, they still have a long way to go.
"It's easy to design a robot that people find very difficult," says Seminatore. "I can design a robot that can lift 2,000 pounds no problem ... but it's the simple things that robots really have a lot of trouble with."
The lab demonstrated SAFFiR to the Navy in November and is ramping up for Phase Two. Seminatore doesn't expect a finalized product for ten to 15 years, but in the mean time, they will take to the robotics challenge with ESCHER hoping to put on a good show, demonstrating what the future may hold for the Navy's firefighting robot.
By Melissa Fassbender, Editor
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|Title Annotation:||Engineering Answers: ROBOTICS|
|Publication:||Product Design & Development|
|Date:||Apr 1, 2015|
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