Post Cook Islands Bedrock and Soil Science Studies, The 3rd leg in our Journey to Endeavour Crater |
Post Cook Islands Bedrock and Soil Science Studies, The 3rd leg in our Journey to Endeavour Crater |
May 4 2009, 08:07 PM
Post
#121
|
|
Member Group: Members Posts: 530 Joined: 21-March 06 From: Canada Member No.: 721 |
Hey, when Two Guys from Canada both suggest the same thing, they've got to start thinking it might be a good idea.
|
|
|
May 4 2009, 08:12 PM
Post
#122
|
|
Solar System Cartographer Group: Members Posts: 10172 Joined: 5-April 05 From: Canada Member No.: 227 |
That's right, eh, you hosers!
Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PD: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
|
|
May 4 2009, 08:14 PM
Post
#123
|
|
Member Group: Admin Posts: 976 Joined: 29-September 06 From: Pasadena, CA - USA Member No.: 1200 |
... To me it seems this would be a really tough call. How do you quantify the advantages of driving faster now, versus extending the life of the wheel to allow greater maneuverability later? Actually, it may be moot at the moment, since negotiating even the current moderate ripples may be a big problem with five wheels. But then I suppose that would be simple enough to test with a short experimental drive using 5 wheels. Perhaps voluntary 5-wheel driving will become a good option once we get to the flat parking lot terrain. I agree. In this type of terrain we need as much heading control as we can. Once on the parking lot maybe we can relax a bit. If the issue is the number of thermal cycles, not the number of wheel revolutions, then the answer is pretty clear (use it while you can!). Paolo -------------------- Disclaimer: all opinions, ideas and information included here are my own,and should not be intended to represent opinion or policy of my employer.
|
|
|
May 4 2009, 09:31 PM
Post
#124
|
|
Senior Member Group: Members Posts: 4247 Joined: 17-January 05 Member No.: 152 |
|
|
|
May 4 2009, 09:38 PM
Post
#125
|
|
Member Group: Members Posts: 507 Joined: 10-September 08 Member No.: 4338 |
Any thoughts on why the right front wheel seems to be more vulnerable than the other wheels?
|
|
|
May 4 2009, 09:46 PM
Post
#126
|
|
Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
1:6 says that the first wheel to get trouble will be the same on both rovers.
|
|
|
May 4 2009, 09:57 PM
Post
#127
|
|
Dublin Correspondent Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 |
I think the odds are actually lower than that - the front two wheels are likely to be a bit more stressed in general so I'd have thought it was closer to a 50:50 chance. But you are right - it's 1 in 6 assuming all wheels are equal which means we can't read anything into it with just two data points.
|
|
|
May 4 2009, 09:58 PM
Post
#128
|
|
Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
Maybe even shorter odds. The corners could be be more vulnerable than the middle wheels.
EDIT Nice one helvick, you beat me to it there. |
|
|
May 4 2009, 10:04 PM
Post
#129
|
|
Director of Galilean Photography Group: Members Posts: 896 Joined: 15-July 04 From: Austin, TX Member No.: 93 |
Assuming there are no dependent variables between the wheels. But I think the front wheels had to do more "unfolding" out of the stowed position versus the middle or rear wheels. Maybe that is a factor? Plus, the weight distribution might not be symmetrical, with one side heavier than the other due to the robotic arm (it comes out from the right, correct?) and the pancam mast (front vs back). If MSL's first wheel failure is the right front, then we know there's a conspiracy.
-------------------- Space Enthusiast Richard Hendricks
-- "The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke Mother Nature is the final inspector of all quality. |
|
|
May 4 2009, 11:03 PM
Post
#130
|
|
Member Group: Members Posts: 399 Joined: 28-August 07 From: San Francisco Member No.: 3511 |
... so how many wheels need to fail before the rover can't rove ?
Would a Left Rear freeze do that? -------------------- 'She drove until the wheels fell off...'
|
|
|
May 5 2009, 12:19 AM
Post
#131
|
|
Member Group: Admin Posts: 976 Joined: 29-September 06 From: Pasadena, CA - USA Member No.: 1200 |
... so how many wheels need to fail before the rover can't rove ? Would a Left Rear freeze do that? I actually went to the ISIL to do some testing to answer this question a couple of years ago. For sure this depends a lot on soil type, but in the testing I have done, if you lose two driving actuators you immediately become a lander. Of all the wheels to lose, the front wheels are the one that cause less trouble (the rocker is longer than the bogie) and they can be seen in the FHAZ (the RR can't be seen very well in the RHAZ). Between the rear and middle, losing one of the middle wheels has the advantage of having the same difficulties in driving forwards vs backward and causes less heading change when trying to drive straight. The loss of one of the rear wheels would probably be worst, less visibility in the RHAZ and driving backwards would probably be a mess since you would immediately pop a wheelie effectively driving only with four active wheels. As a side note, I also tried to drive the testbed on pavement Spirit-like and do typical Opportunity-like turn-in-place and neither of these activities are look pretty to the eye or to the ear: the grinding noise and the amount of deflection on the rocker is amazing! Paolo -------------------- Disclaimer: all opinions, ideas and information included here are my own,and should not be intended to represent opinion or policy of my employer.
|
|
|
May 5 2009, 06:25 AM
Post
#132
|
|
Member Group: Members Posts: 399 Joined: 28-August 07 From: San Francisco Member No.: 3511 |
Thanks for taking the time to answer..
.. so wonderfully informative! Best of luck MER team.., Eoin -------------------- 'She drove until the wheels fell off...'
|
|
|
May 5 2009, 03:10 PM
Post
#133
|
|
Director of Galilean Photography Group: Members Posts: 896 Joined: 15-July 04 From: Austin, TX Member No.: 93 |
As a side note, I also tried to drive the testbed on pavement Spirit-like and do typical Opportunity-like turn-in-place and neither of these activities are look pretty to the eye or to the ear: the grinding noise and the amount of deflection on the rocker is amazing! Paolo *Sigh* Youtube was just a little bit too late... -------------------- Space Enthusiast Richard Hendricks
-- "The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke Mother Nature is the final inspector of all quality. |
|
|
May 5 2009, 03:35 PM
Post
#134
|
|
Senior Member Group: Moderator Posts: 3431 Joined: 11-August 04 From: USA Member No.: 98 |
*Sigh* Youtube was just a little bit too late... I still have nightmares after seeing the engineering model (or maybe it was a simulation, I don't recall) driving with 5 wheels in the "Five Years on Mars" special. Okay, not literally, but ouch... that was painful to see. |
|
|
May 5 2009, 08:22 PM
Post
#135
|
|
Member Group: Members Posts: 507 Joined: 10-September 08 Member No.: 4338 |
1:6 says that the first wheel to get trouble will be the same on both rovers. Assuming randomness, though, we would expect to see increased signs of wear, such as occasional elevated currents, on the other wheels before too long after the first, right? Is it reasonable to invoke randomness when one wheel has serious trouble long before the others show the slightest sign of trouble? |
|
|
Lo-Fi Version | Time is now: 30th May 2024 - 04:26 PM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |