By Melissa Fassbender, Editor
THE CHALLENGES OF DESIGNING
A FIREFIGHTING ROBOT R O B O T I C S
SAFFiR was tested (page right) on the former USS
Shadwell (below), a decommissioned U.S. Navy landing ship that now serves as full-scale damage control
research center to test new shipboard fire-fighting
techniques. (All image credit: Virginia Tech College of
The Shipboard Autonomous Firefighting Robot (SAFFiR) is a humanoid
robot designed by the Terrestrial
Robotics Engineering and Controls
Lab (TREC) at Virginia Tech.
Designed for the Navy, the lab
realized that with a few changes,
the robot could also
compete in the DARPA robotics
challenge (DRC) for a chance to
win $2 million. Soon thereafter,
the team began designing
ESCHER, an Electromechanical
Series Compliant Humanoid for
"It seemed like killing two birds with one stone," says John
Seminatore, graduate researcher at the TREC 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 stu-dents," 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,"