ALGOR SOFTWARE ENABLES DANTE TO DESCEND INTO HIS INFERNO

Dante II scales a rugged hillside on a field test before being sent into Mount Spurr, an active volcano in Alaska. The frame and leg joints were optimized with Algor.

In July 1994, Dante II, an eight-legged robot, made a well-publicized descent into Mount Spurr, an active volcano 80 miles from Anchorage, Alaska.

People all over the globe watched on TV and read in newspapers about the robot's painstaking climb 700 feet down the boulder- and gully-lined surface of the crater.

This amazing task was accomplished with Algor finite element analysis software, NASA funding and the talent of engineers at Carnegie Mellon University's (CMU) Robotics Institute in Pittsburgh, Pennsylvania.

New and Improved

Dante II is actually the "new and improved" version of its predecessor, Dante I, which attempted a similar descent into Antarctica's Mount Erebus in 1993.

Working on UNIX-based SUN workstations, engineers at CMU, one of the nation's forerunners in robotics technology, used Algor software to optimize the weight and strength of Dante II's components.

Improvements over Dante I included a different gait and leg configuration, stronger legs, updated software and a stronger winch and rappelling cable.

The Importance of Analysis

"Robotic exploration is a field where many factors can determine the success or failure of a project," said John Bares, principal investigator of Dante II. "With so many unanticipated events that can occur in the field, the last thing you want to worry about is whether or not your robot's structures will hold up.

Robotics engineers saved precious weight by reducing the amount of material used in support structures such as this. The frame shown above is visible on Dante II's right side(see figure of Dante at top of page).

Walk This Way

The 1700-pound Dante II walks on two sets of four legs with the aid of a tether that both provides a communications link and adds stability. While the original Dante had four legs on each side, Dante II has four legs each in the back and front. The body is partitioned into two frames, each of which is linked to four legs.

To understand Dante's "frame walker" leg configuration, picture two coffee tables, nested one inside the other. The robot rests on one set of four legs, while the other set slides forward. The second set of legs then lowers and the first is raised for the next step.

An Optimal Frame Structure

Algor software was used to test the design for many of Dante II's frame structures. These frame structures were originally designed as solid sheets of aluminum alloys. When the analyses indicated low stresses in the frames, engineers removed material from the sheets to reduce weight while maintaining safe margins of structural strength.

"From the stress analyses we performed using Algor software, we learned that in some structures we could reduce bulk, while in others, we had to add material to reduce stresses in the design," said Dimitrios Aposto-lopoulos, a member of the Dante design team.

Optimizing the Leg Joints

For the leg mechanisms, the CMU engineers needed to change the design to meet the difficult performance requirements of walking on the rough, steep slopes of the volcano. Finite element analysis revealed that the original leg joint design would not be strong enough to withstand the difficult terrain. Based on these findings, fork-like joints were designed resulting in nearly a three-fold increase in strength and stiffness.

The new fork-like design (shown in center frame) of Dante's leg joints resulted in nearly a three-fold increase in strength and stiffness. Algor analysis results were confirmed by prototype testing.

Algor Results Confirmed by Field Tests

"The results from preliminary loading tests of the prototype legs were in close agreement with the analysis results," said Mr. Apostolopoulos.

"Our strong confidence in Algor software was reinforced when we measured body deflections during our field trials of Dante II. The results from these real-world tests also matched closely with the analysis results.

Dante Saves Lives

Harsh volcano craters claimed the lives of eight volcanologists in 1993. Mount Spurr, which has erupted three times since 1992, was deemed too dangerous for human scientists to enter.

Because of Mount Spurr's close proximity to Anchorage, scientists wanted to determine if the volcano would be spewing toxic ash again in the near future. Dante II provided a safe, effective way of obtaining the necessary scientific data.

Human scientists only needed to get to the rim of the crater, where they set up a telecommunications dish and a generator. They then sent Dante II on its way.

Behind the Scenes

Dante's on-board scanning laser rangefinders and eight video cameras transmitted images and data to scientists in Anchorage and to the NASA Ames Research Center in San Francisco.

The data from the rangefinders was rendered into an elevation map of the terrain surrounding the robot. This map was then superimposed with a three-dimensional kinematic model of Dante II to produce a virtual reality environment. Scientists, students, members of the press and robot operators viewed images from Dante's on-board video cameras on a stereoscopic monitor through special glasses.

Artificial Intelligence

Scientists provided a general plan for Dante's mission, but the robot's artificial intelligence took care of many of the details. The robot autonomously controlled the force, height, and placement of each step by correlating data from leg sensors and laser rangefinders. Dante was able to choose a specific path, walking over one meter boulders and around taller objects. The tension of the communications/rappelling cable was adjusted using on-board winch sensors and controls.

Mount Spurr was the perfect assignment for Dante II: too dangerous for human scientists but important to study because of its proximity to Anchorage, Alaska.

Getting There...

Dante II, which was airlifted to the rim of the crater by the Alaskan National Guard, began its perilous journey, creeping into the crater at about one half meter per minute. After reaching the crater floor, the robot took temperature readings and sampled volcanic gases.

As a result of the data Dante II delivered, it was determined that Mount Spurr will probably remain inactive in the near future. More importantly, all of this was accomplished without endangering human life.

...and Back Again

When Dante had nearly completed its ascent back up the volcano, a steep gully caused the robot to lose its "footing" and tip over when it was a mere 150 meters from the lip of the crater. Volunteers ventured in to attach a harness, and a helicopter airlifted the robot out of the crater.

Although Dante II did not complete its ascent to the top of the crater, the robot successfully met its mission objectives:

• Show the capabilities of robots to explore steep and challenging terrain.
• Demonstrate the ability to operate in harsh environments.
• Implement various control methods ranging from human remote control to fully autonomous robotic control.
• Perform volcanic scientific analysis using robotically-deployed equipment.

Dante's Future is in the Stars

NASA hopes Dante's experience in the inferno of Mount Spurr is just a small step on the way to the planets. Volcanoes are a good pre-extraterrestrial testing ground because the rugged terrain and harsh environment represent challenges which a robot would have to face in space.

"Our hope," said a spokesperson for NASA's Telerobotics Program, "is that a lot of this (technology) will find its way into future planetary missions. That's obviously where NASA's interests lie. We want to move this out onto other heavenly bodies: the moon, Mars and other planets.

About Algor

"We chose Algor software because Algor had a reputation for high quality at a low cost," said Bares. "Our grant funds limited the time and resources we could spend on design and analysis.

"We are very pleased with the results from the software which eventually contributed to the successful completion of the Dante mission," said Bares.

Copyright © 1995 Algor, Inc. All rights reserved.