Newsgroups: comp.robotics
Path: brunix!cat.cis.Brown.EDU!agate!ames!kronos.arc.nasa.gov!doctor
From: doctor@kronos.arc.nasa.gov (Terry Fong)
Subject: Dante II - Mt. Spurr Expedition Status (12-Jul-94)
Message-ID: <1994Aug23.211950.3028@ptolemy-ethernet.arc.nasa.gov>
Summary: status information on CMU/NASA volcano robot explorer
Keywords: Dante, teleoperations, volcano, Alaska
Sender: usenet@ptolemy-ethernet.arc.nasa.gov (usenet@ptolemy.arc.nasa.gov)
Nntp-Posting-Host: tardis.arc.nasa.gov
Organization: NASA Ames Intelligent Mechanisms Group
Date: Tue, 23 Aug 1994 21:19:50 GMT
Lines: 125

The following is a status update on the Dante II project. Dante II is
an eight-legged robot (developed by the CMU Robotics Institute with
sponsorship from NASA) which is currently descending into the active
crater of Mt. Spurr, an Alaskan volcano 80 miles west of Anchorage,
Alaska. The primary objective of the Dante II project is to develop and
evaluate new techniques and technologies which can be applied to space
and planetary exploration. 

Throughout the Mt. Spurr expedition, Dante II is being remotely
operated from a base station in Anchorage using control station
software developed at CMU and NASA Ames. Live video coverage is
periodically available via NASA Select. Full mission details including
current status, real-time images/video, and technical data is available
via a WorldWideWeb server provided by the NASA Ames Intelligent
Mechanisms Group. This site can be accessed on the Internet using
information browsers such as NCSA Mosaic and the URL:

	http://maas-neotek.arc.nasa.gov/dante

Questions regarding the Dante II project may be addressed to me via email 
(terry@ptolemy.arc.nasa.gov). Reponse time may be slow.

Terry Fong
NASA Ames Research Center

------------------------------------------------------------------------------

Status Report (06-Aug-94 to 10-Aug-94)

As noted in the last Dante Status Report (Friday, August 5), Dante
tipped over in a steep sided ravine at 6:37pm ADT.  Although Dante
was apparently undamaged, it was incapable of righting itself from
its position.  Dante's cameras and science sensors continued to 
function.  All computing was operational and data recorded onboard 
was successfully down-loaded to Anchorage.

A thorough analysis of logged information on Saturday, August 6 has
revealed the series of events which led to the tip over.  Dante was
climbing downhill, backing up after two unsuccessful attempts to scale
a boulder pile uncovered in the recent snow-melt.  Dante was on the
bank of a steep sided ravine with a downhill slope of approximately 30
degrees. Due to the nature of the ravine, a significant cross-slope
(left-to-right) was also present. Since the tether provides support
primarily in the downhill direction, Dante compensates for
cross-slopes by adjusting left and right leg heights to maintain a
level body posture.

Each step in the soft terrain led to small amounts of foot sinkage and
tipping of the robot as the weight was shifted among the legs.  At 6:35pm
ADT operators issued a standard corrective move to redistribute leg
loading after Dante was found to have shifted its weight onto its
left (downhill) legs. As the right (uphill) legs reestablished 
contact, the left legs started to sink further and slip in the soft terrain.
Dante's posture rapidly destabilized, and the robot tipped over in a period 
of several seconds.  

A combination of the leg placement command, unfavorable tether angle,
and soft terrain explain the fall. There were no indications of
hardware or software failure causing or contributing to the tipover.

It should be noted that it there were incorrect reports in the
media that Dante had broken a leg or that mechanical failure caused
the collapse.  We have no evidence of any damage at all.  Dante
appeared to be functioning normally,... on its side.

Saturday and Sunday, (August 6 and 7) were spent analyzing the tip
over and the disassembling the Dante Anchorage base station.  We also
took some much needed rest and a number of Dante team members departed
from Alaska over the weekend.

On Monday, August 8, the Army National Guard flew to Mount Spurr
to retrograde gear back to Anchorage.  Our plan was to pick up Dante
by the end of its tether (the end normally attached to the anchor) and
lift it from the crater.  By attaching to the tether at the anchor
point, no one would have to approach the robot.  At the point of
tipover Dante had climbed more that 200 feet from the crater floor but
was still approximately 350 below the crater rim.  Dante's tether is
Kevlar fiber reinforced and has undergone extensive testing of its
strength, flexiblity and abrasion resistance.  The breaking strength
of the tether is in excess of five times Dante's weight (1700 pounds).

National Guard helicopters arrived at Mount Spurr's rim and rigged the
anchor end of the tether for lift.  However, steam and cloud cover
obscured the crater and Dante.  Although the helicopters are equipped
for flight in low visibility (IFR), clear skies were deemed necessary
to view Dante while being lifted and slung 400 feet below the
helicopter. The weather did not clear for the remainder of the day.

On Tuesday, August 9, teams returned for the lift.  At approximately
11:00am ADT, the tether was attached to the lift point of an Army
National Guard Blackhawk helicopter.  The helicopter flew down the
tether's route rising to lift the tether from the ground.  Once above
Dante, the helicopter began to rise vertically.  It lifted the robot
so that it hung with tether exit (back end) up and the robot facing
down.  As the tether tensioned, it broke, an estimated four feet from
the robot exit point.  Dante dropped, and rolled onto its right side
and then onto its back.  Dante is now 10-15 feet from the point of
initial tipover with its legs in the air.  A brief flyby showed the
robot to be mostly intact but with some apparent damage. The cause for
the tether break has not yet been explained. A close examination of
the severed tether ends may provide some insights.

With available helicopters, focus shifted to recovering the remaining
equipment at the rim (generator, communications satellite and rim
electronics). While coiling cable between the generator and rim
electronics, CMU team member Tim Hegadorn slipped in the wet muddy
terrain and suffered a broken leg. He was immediately evacuated by a
second Army National Guard helicopter already present and treated at
Alaska Regional Hospital. It should be noted that neither Hegadorn nor
anybody else had descended below the rim of the volcano and his 
unfortunate accident was unrelated to the robot recovery attempt.

The remaining personnel were able to airlift the power generator with
the Blackhawk helicopter before the weather once again forced an early
end to operations at the volcano for the day. 

No further recovery operations are scheduled for Wednesday, August 10,
as options for recovering Dante are being considered.


-- 
_______________________________________________________________________________
 "San Francisco has only one           Terry Fong <terry@ptolemy.arc.nasa.gov>
  drawback - it's hard to leave..."    NASA Ames, M/S 269-3, Moffett Field, CA
                -- Rudyard Kipling          (415) 604-6063, (415) 604-6081 lab
