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Slip Sliding Away (Mars Rovers)



 
 
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  #1  
Old March 11th 04, 04:20 AM
Ron
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Default Slip Sliding Away (Mars Rovers)

http://marsrovers.jpl.nasa.gov/spotl..._20040309.html

Slip Sliding Away
Jet Propulsion Laboratory
March 09, 2004

On February 9, the wake up song for Opportunity was 'Slip
Sliding Away' by Simon and Garfunkel in honor of the
experience the prior day when Opportunity first tried to scoot
up the crater slope at Meridiani Planum. The ambitious rover
aimed for its target and willingly went forth up the slope;
nevertheless, Opportunity slipped and slid in the sand,
making it only half way to its target.

But ignorance is bliss, and while Opportunity's wheels had a
hard time gaining traction on the sandy surface, the rover's
brain (or computer) had a hard time grasping that it hadn't
successfully made it to its target. The little rover didn't have
to encourage itself to make it up the crater slope later by
chanting, "I think I can, I think I can," because the little rover
thought it actually did make it up the slope the first time.

Measuring the Distance Traveled on Mars

"Like a car on Earth, each Mars rover uses an odometer to
click off the distance its wheels travel to measure and
register how far the vehicle has moved," explains Randy
Lindemann, rover mobility lead. One revolution of the rover
wheel equals 80 centimeters or 2.6 feet, so after the wheels
have revolved four times, the rover believes that it has
moved forward 320 centimeters or 10.5 feet (80 centimeters
X 4 = 320 centimeters).

Alas, Opportunity's wheels had a hard time grasping onto
the sandy ground around the crater and the wheels spun in
place before they actually gained tracking. "As Opportunity's
wheels turned and ticked off 80 centimeters (2.6 feet) each
revolution, they eventually spun four times, calculating to
what it thought was a distance of 320 centimeters (10.5
feet). Thus, Opportunity believed it had reached its goal,
when in reality, it had spun in place 50 percent of the
revolutions and only really made it 160 centimeters (5.25
feet)," said Lindemann.

Outwitting the Odometer

In order to prevent any future missed targets, Opportunity's
mobility experts quickly started trying to predict exactly how
far the rover would slip down a slope or fall short of a target
while climbing up a slope due to the loose terrain along the
steep angles of the crater wall. "Since the rover isn't on
cruise control and can't rev its engine to get some extra
oompf to go up a hill, we continually have to outwit
Opportunity's odometer and command the rover to go farther
or shorter than the real target distance," said Rover Driver
Eric Baumgartner.

Rover Drivers and their Crystal Ball

"Well, we don't quite have a crystal ball to predict slippage
of the rover wheels," said Lindemann, "but our team of
mobility experts and rover drivers can make predictions
using a rather nice piece of paper with a curved line on a
standard plot."

How well does this prediction on paper work? It's all about
prior testing. While Opportunity was cruising through deep
space on the way to Mars, engineers on Earth tested the
rover's mobility using an engineering model of the rover of
the same weight and size with identical wheels. Engineers
affectionately named it the "SSTB-lite rover." SSTB-lite
stands for Surface System TestBed, and the lite means that
this rover doesn't have any of the appendages, such as the
robotic arm, high-gain antenna, or panoramic camera mast
assembly.

"Our sandbox was a variable-tilt platform covered with 6
inches of dry, loose sand similar to what is used with
construction cement. Throughout the weeklong test, we
plotted how much the test rover slipped at different
angles going up, down and across the simulated martian
terrain," explained Lindemann.

"We never expected the incredible result that the rover's
slipping behavior at the Meridiani site would be almost
identical to its behavior on dry and loose sand. The reason
that this surprised us so much is that the soil at Meridiani
is nothing like dry beach sand from the Earth in terms of
the minerals that it is made of or even how it was formed.
What we have learned is that the primary characteristic of
any loose soil in terms of how the rover will drive on it
is determined by the characteristics of the friction between
all of the tiny grains -- pretty much no matter what they
are made of," said Lindemann.

How Far Will Rovers Slip and Slide?

The test created a set of trustworthy mobility plots. The
plots show rover drivers that, at a 15-degree angle facing
down, the rover will slide an extra 25 centimeters downward
for every meter it is trying to go. The chart is not a straight,
even line. At a 20-degree angle downward, the rover will
slide 55 centimeters (1.8 feet) down, whereas at 20-degree
angle upward, the rover will slip 90 centimeters (2.9 feet) in
place and only move forward 10 centimeters (3.9 inches) out
of a drive of 100 centimeters (3.3 feet).

"For the type of sand Opportunity is in, the dead-end point
where the rover simply can't climb upwards anymore,
regardless of how many times the wheels turn, is 25
degrees," explained Baumgartner. "We've already gone up
slopes as steep as 22 degrees on Opportunity Ledge.
Luckily, the Long Term Planning team has found places
around the crater with slopes lower than 25 degrees, so we
can eventually get out of this crater where we landed," said
Baumgartner.

Driving Spirit Versus Opportunity

Baumgartner is one of eight rover drivers. There are four for
Spirit and four for Opportunity. Two rover drivers are on
station for any given sol. "It's a lot of fun to come to work
and drive the rovers on Mars and drive the rover arm, which
is a whole other story in itself," said Baumgartner. The rover
drivers for the two rovers have had very different
experiences due to the difference in terrain at the two sites.

"At the Opportunity site, it's like we're driving on snow
with little traction on the slopes, but the Spirit site is like
monster truck driving with the rocky terrain," laughed
Baumgartner.

Spirit is on flat, rocky terrain, while Opportunity is in steep
terrain with a low distribution of rocks, so the two rover
driving teams will be swapping lessons learned when each
rover moves to a different location. "If Spirit makes it to
Bonneville crater, the rover drivers will have to rely on what
we've learned at Meridiani, and once we get out of the crater
at Meridiani, we may need to learn how to drive far in a
rock-strewn landscape from the Spirit team," said
Baumgartner.

On Your Mark, Get Set, Rove!

In order to build the drive commands for Spirit and
Opportunity, rover drivers use sophisticated software
created at NASA's Jet Propulsion Laboratory to make a
three-dimension simulation of the martian terrain using
navigation camera images and a simulation of the actual
movement of the rover. Rover drivers must simulate the
rover movement in a computer program because there isn't
enough time to sprint to a test bed (a sandbox with an
engineering rover model) every day to run the command
sequence. Schedules are extremely tight to turn around new,
complex robot moves and send the commands to a planet
over 150 million miles away.

"We run many, many simulations -- up to 20 per move --
to figure out what the best path is for each segment of the
drive," explains Baumgartner. Rover drivers for Opportunity
have to add in the slippage estimates created by the mobility
experts. Rover drivers use the slope information and tell the
rover to stop short of its target when it's heading down a
slope so that the rover will slide into home plate on its own.
When the rover has to trek up a slope, engineers do the
opposite since it is harder for the wheels to churn upward. If
the rover needs to go up a slope, engineers command the
rover to actually go farther than necessary to compensate for
the upward tilt.

"I didn't think adding in slippage would be part of my work
as a rover driver," said Baumgartner. "The foresight of
mechanical team was tremendous, and if we didn't have the
slippage chart, we would be putting our thumbs to the air and
saying, 'I think the rover will slip about this much here,'"
laughed Baumgartner. "Within about five hours every day,
we have to write hundreds of lines of commands to drive the
rover to the scientists' dream location. Without the efficient
slip estimates, which the mobility team constantly refines,
we would be in a lot of trouble here," said Baumgartner.

Body Movin?

On February 18, the wake up song for Opportunity was "Body Movin"
by the Beastie Boys in honor of the 15-meter (49-foot) drive,
which was Opportunity's farthest distance to date. "We were off
by less than 0.5 meters (1.6 feet) from our desired final
destination, which is an error of about 3%. In contrast,
Opportunity actually slipped between 10% and 17%, so without
this slippage planning, we would have been off by as much as
2.6 meters (8.5 feet). That would have cost us another day on
Mars to get close enough for the pancam and mini-TES work that
was planned at the target," said Lindemann.

"We've moved from sad folk music to body movin' rap music for
wake up songs, so I'm pretty happy," said Lindemann with a smile.
  #2  
Old March 11th 04, 02:43 PM
mlm
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Posts: n/a
Default Slip Sliding Away (Mars Rovers)

(Ron) wrote in
om:

http://marsrovers.jpl.nasa.gov/spotl..._20040309.html

Slip Sliding Away
Jet Propulsion Laboratory
March 09, 2004

On February 9, the wake up song for Opportunity was 'Slip
Sliding Away' by Simon and Garfunkel in honor of the
experience the prior day when Opportunity first tried to scoot
up the crater slope at Meridiani Planum. The ambitious rover
aimed for its target and willingly went forth up the slope;
nevertheless, Opportunity slipped and slid in the sand,
making it only half way to its target.

But ignorance is bliss, and while Opportunity's wheels had a
hard time gaining traction on the sandy surface, the rover's
brain (or computer) had a hard time grasping that it hadn't
successfully made it to its target. The little rover didn't have
to encourage itself to make it up the crater slope later by
chanting, "I think I can, I think I can," because the little rover
thought it actually did make it up the slope the first time.


All very nice Ron. Thanks again for sending on this detailed
explanation.

What is the message to draw from this? The rovers are incredibly stupid.
Perhaps, in fairness to the poor things, one should say that they have
incredibly stupid decision making software running them. Even the
vaunted independent navigation system is incredibly crude when you think
about it.

One wonders how much it would take to enable the rover to figure out that
it was not really moving as far as it thought. What about using
accelerometer data? Images? Doesn't the independent nav system look at
obstacles in the rover's path? If so, why can't it just figure out that
the obstacles haven't changed much despite the odometer clicking off 20
metres (65 feet for the metrically clueless).

Fact is these things are really only elaborate extensions of their
engineers egos. Far from the independent robots they are made out to be.
Highly capable machines that don't really have a clue. A lot like pro
wrestlers.

Mark
  #3  
Old March 11th 04, 07:33 PM
Keith Lehman
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Default Slip Sliding Away (Mars Rovers)

On 10 Mar 2004, Ron wrote:

http://marsrovers.jpl.nasa.gov/spotl..._20040309.html

Slip Sliding Away
Jet Propulsion Laboratory
March 09, 2004

On February 9, the wake up song for Opportunity was 'Slip
Sliding Away' by Simon and Garfunkel in honor of the


Slip Sliding Away was done by Paul Simon after he went solo.


  #4  
Old March 11th 04, 09:42 PM
Hud Nordin
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Posts: n/a
Default Slip Sliding Away (Mars Rovers)

In article ,
Keith Lehman wrote:
On 10 Mar 2004, Ron wrote:

http://marsrovers.jpl.nasa.gov/spotl..._20040309.html

Slip Sliding Away
Jet Propulsion Laboratory
March 09, 2004

On February 9, the wake up song for Opportunity was 'Slip
Sliding Away' by Simon and Garfunkel in honor of the


Slip Sliding Away was done by Paul Simon after he went solo.


So you're saying they never recorded it together?

http://www.lyricsfreak.com/s/simon-a...el/124691.html
--
Hud Nordin Silicon Valley
  #5  
Old March 11th 04, 10:09 PM
Henry Spencer
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Default Slip Sliding Away (Mars Rovers)

In article , mlm wrote:
One wonders how much it would take to enable the rover to figure out that
it was not really moving as far as it thought. What about using
accelerometer data? Images?


Accelerometers that will precisely measure very small accelerations --
the rovers don't move very quickly, and their acceleration is very small
indeed -- are complex, heavy, and costly. Not something you put on a
low-budget low-mass rover, especially when the need should be rare.

And automatic image analysis is really very difficult. Yes, something
might be devised for this particular situation... but why bother, unless
it's going to happen every other day?
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |
  #6  
Old March 11th 04, 11:16 PM
Greg Crinklaw
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Default Slip Sliding Away (Mars Rovers)

mlm wrote:
Fact is these things are really only elaborate extensions of their
engineers egos. Far from the independent robots they are made out to be.
Highly capable machines that don't really have a clue. A lot like pro
wrestlers.


Please show us the robots and decision making software that you have
designed, Mr. know-it-all.

Yeah. Thought so.

  #7  
Old March 12th 04, 12:04 AM
Ben Bradley
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Posts: n/a
Default Slip Sliding Away (Mars Rovers)

In comp.robotics.misc, mlm wrote:

(Ron) wrote in
. com:

http://marsrovers.jpl.nasa.gov/spotl..._20040309.html

Slip Sliding Away
Jet Propulsion Laboratory
March 09, 2004

On February 9, the wake up song for Opportunity was 'Slip
Sliding Away' by Simon and Garfunkel in honor of the
experience the prior day when Opportunity first tried to scoot
up the crater slope at Meridiani Planum. The ambitious rover
aimed for its target and willingly went forth up the slope;
nevertheless, Opportunity slipped and slid in the sand,
making it only half way to its target.

But ignorance is bliss, and while Opportunity's wheels had a
hard time gaining traction on the sandy surface, the rover's
brain (or computer) had a hard time grasping that it hadn't
successfully made it to its target. The little rover didn't have
to encourage itself to make it up the crater slope later by
chanting, "I think I can, I think I can," because the little rover
thought it actually did make it up the slope the first time.


All very nice Ron. Thanks again for sending on this detailed
explanation.

What is the message to draw from this? The rovers are incredibly stupid.
Perhaps, in fairness to the poor things, one should say that they have
incredibly stupid decision making software running them. Even the
vaunted independent navigation system is incredibly crude when you think
about it.

One wonders how much it would take to enable the rover to figure out that
it was not really moving as far as it thought. What about using
accelerometer data? Images? Doesn't the independent nav system look at
obstacles in the rover's path? If so, why can't it just figure out that
the obstacles haven't changed much despite the odometer clicking off 20
metres (65 feet for the metrically clueless).

Fact is these things are really only elaborate extensions of their
engineers egos. Far from the independent robots they are made out to be.


I would have expected a (or several) more reliable system for
measuring distance, such as some sort of radio distance ranging from
the base/platform (is it running or does it have any active
electronics in it after the rover goes down the ramp?) or Mars
sattelite, and/or a downward-facing camera and logic system such as in
a modern-day optical mouse, or looking at obstacles as you described.
OTOH, there's the engineering idea that the more complex something
is, the more likely it is to break down. They probably have opto
quadrature detectors in each wheel to detect its direction and speed,
which surely also detects stalled wheels and such, so using that for
distance measurement is 'good enough.'

Highly capable machines that don't really have a clue. A lot like pro
wrestlers.


Now you've insulted both pro wrestlers AND the rovers!

Mark


-----
http://mindspring.com/~benbradley
  #8  
Old March 12th 04, 02:08 AM
Robert Casey
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Posts: n/a
Default Slip Sliding Away (Mars Rovers)

Henry Spencer wrote:

In article , mlm wrote:


One wonders how much it would take to enable the rover to figure out that
it was not really moving as far as it thought. What about using
accelerometer data? Images?



Accelerometers that will precisely measure very small accelerations --
the rovers don't move very quickly, and their acceleration is very small
indeed -- are complex, heavy, and costly. Not something you put on a
low-budget low-mass rover, especially when the need should be rare.

And automatic image analysis is really very difficult. Yes, something
might be devised for this particular situation... but why bother, unless
it's going to happen every other day?


Analyzing images in real time still takes a small brain to do. Though
insects and small fish
can do it, so it can't be as hard as some of the things human brains do
routinely. At
least the rover didn't tilt or fall over. Can they recover if they turn
turtle? Depending on
which way, I suppose that instrument arm might be able to help right the
rover. Not on
its own, NASA would have to tell it how. Hopefully nothing gets broken
if it did roll
down the slope....

Can the rover, instead of driving straight up the slope, take it sideways?

  #9  
Old March 12th 04, 02:58 AM
Chosp
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Posts: n/a
Default Slip Sliding Away (Mars Rovers)


"Robert Casey" wrote in message
...

Analyzing images in real time still takes a small brain to do. Though
insects and small fish
can do it, so it can't be as hard as some of the things human brains do
routinely. At
least the rover didn't tilt or fall over. Can they recover if they turn
turtle?


No.

Depending on
which way, I suppose that instrument arm might be able
to help right the rover.


Not anywhere near enough strength where it needs it.
And it would ruin the instruments on the end of the arm.
If it goes over, that's that.


  #10  
Old March 12th 04, 03:45 AM
mlm
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Posts: n/a
Default Slip Sliding Away (Mars Rovers)

Greg Crinklaw wrote in
:

mlm wrote:
Fact is these things are really only elaborate extensions of their
engineers egos. Far from the independent robots they are made out to
be. Highly capable machines that don't really have a clue. A lot
like pro wrestlers.


Please show us the robots and decision making software that you have
designed, Mr. know-it-all.

Yeah. Thought so.



I wish I knew it all. I don't Mr. Cynic, but I do know how to solve
this problem. And I don't need a multimillion dollar software
development budget to do it. Furthermore, the rovers have all the gear
they need. Snap photo. Contrast enhance severely to take out gray
areas. Move. Snap photo. Measure distance between black spots on
photos. Hey presto no movement. Doubt something like this could be
done? How about the DIMES system? Yes it was a late addition but it
proves the concept. It is a software problem. The hardware to do it is
right on the rover.

As was mentioned, coming up short on a drive means another day wasted.
With a budget for the mission of $400 million, each day is worth a lot
of cash. SHould be solvable by a clever engineer with a little extra
midnight oil. Don't even need a know it all.

Mark
 




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