Wheel Trouble, ...down to 5 good wheels? |
Wheel Trouble, ...down to 5 good wheels? |
Mar 14 2006, 04:37 PM
Post
#16
|
|
Junior Member Group: Members Posts: 90 Joined: 13-January 05 Member No.: 143 |
Do we have six clutches on this thing? Can we disengage the motor and free-wheel? The short answer: I'm 99% sure the answer is "no". The long answer: There are two things that resist turning of the wheel when the motor isn't energized: dynamic braking and static detents. Dynamic braking occurs from back-emf in the motor electrical circuit, and provides a resistive torque when the wheel is turned but no force when the wheel is stopped. Dynamic braking can be disengaged in the electrical system. The static detents, on the other hand, are magnets that cause the motor to preferentially stay at certain turn positions. These are necessary to keep the wheels from rolling after the rover comes to a stop, and cannot be disengaged. Because of the high gear ratio of the drive gearbox, it takes a hefty torque to the wheel from the outside to overcome the detent. Bottom line: assuming the motor stall can't be corrected, they will probably have to drive backwards dragging a stuck RF wheel. This is something they have done before in the West Spur area when they were afraid the RF motor was nearing end of life. Though at that time, I think they periodically turned the RF wheel a bit to drive over the buildup of dirt in front of the wheel. |
|
|
Mar 14 2006, 05:53 PM
Post
#17
|
|
Member Group: Members Posts: 688 Joined: 20-April 05 From: Sweden Member No.: 273 |
Design lesson for future rovers: there should be some simple and reliable mechanism for unclutching a wheel once it is certain that it is inoperable and cannot be recovered. Some kind of pyro mechanism perhaps?
tty |
|
|
Mar 14 2006, 06:09 PM
Post
#18
|
|
Senior Member Group: Members Posts: 3008 Joined: 30-October 04 Member No.: 105 |
QUOTE there should be some simple and reliable mechanism for unclutching a wheel... Probably not do-able within the constraints of 'simple and reliable'. Given that the original service life of the Rovers was 90 days and they have lasted a long time, the optimum solution would be to upgrade the motor and geartrain to give a much much longer service life. --Bill -------------------- |
|
|
Mar 14 2006, 07:49 PM
Post
#19
|
|
Senior Member Group: Members Posts: 1887 Joined: 20-November 04 From: Iowa Member No.: 110 |
|
|
|
Mar 14 2006, 08:23 PM
Post
#20
|
|
Member Group: Members Posts: 648 Joined: 9-May 05 From: Subotica Member No.: 384 |
That's good news...if it got in, it can posibly get out of there...Would not be the first time.
-------------------- The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.
Jules H. Poincare My "Astrophotos" gallery on flickr... |
|
|
Mar 14 2006, 08:32 PM
Post
#21
|
|
Dublin Correspondent Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 |
[quote name='alan' post='45573' date='Mar 14 2006, 07:49 PM'] Something in there? [/quote] Looks like a rock stuck in there to me. With some stretching and bending of the luminosity curves there seems to be a fairly irregular potato shaped object jammed in there. If it is a rock is there any chance that it could be jolted loose with some creative driving? B)--> That's good news...if it got in, it can posibly get out of there...Would not be the first time. [/quote] The last one that I recall was this one from Sol 345 |
|
|
Mar 14 2006, 09:34 PM
Post
#22
|
|
Junior Member Group: Members Posts: 90 Joined: 13-January 05 Member No.: 143 |
Something in there? That's really encouraging! Now I think (hope) I overreacted to the initial description I heard of the problem. At that time it sounded like there was evidence in the telemetry that the motor circuit had failed "open", which suggested a broken wire or brush inside the motor. By comparison, unsticking a rock sounds easy. I knew I should keep my virtual mouth shut and wait for more data. |
|
|
Mar 14 2006, 09:46 PM
Post
#23
|
|
Dublin Correspondent Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 |
|
|
|
Mar 14 2006, 09:46 PM
Post
#24
|
|
Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
That's really encouraging! Now I think (hope) I overreacted to the initial description I heard of the problem. At that time it sounded like there was evidence in the telemetry that the motor circuit had failed "open", which suggested a broken wire or brush inside the motor. By comparison, unsticking a rock sounds easy. I knew I should keep my virtual mouth shut and wait for more data. I hope that's a rock too, but none of it is out in the light looking clearly 'rocky'. I hate to suggest it might just be some internal reflection - like my...er...flying saucer. -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
|
|
|
Mar 14 2006, 10:05 PM
Post
#25
|
|
Dublin Correspondent Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 |
|
|
|
Mar 14 2006, 10:34 PM
Post
#26
|
|
Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
And just in case we get too optimistic: Example 1 Example 2 There's shading in both of these in exactly the same place and the lighting is from a similar direction. ...And the pendulum swings... http://static.flickr.com/36/112580016_7b9d7405a1_o.jpg Somebody in another forum doing some more intensive photoenhancement. (Like looking for WMDs) -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
|
|
|
Mar 14 2006, 10:37 PM
Post
#27
|
|
Dublin Correspondent Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 |
|
|
|
Guest_Sunspot_* |
Mar 14 2006, 10:55 PM
Post
#28
|
Guests |
I thought it might have been a rock at first... but now i'm thinking it is probably some internal reflection too
|
|
|
Mar 14 2006, 11:05 PM
Post
#29
|
|
Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
At a first look - it just looks like dust to me - and the two sets of diagnostic images ( one presumes before and after a commanded rotation of the wheel ) show no change in the position of the wheel
Doug |
|
|
Mar 14 2006, 11:06 PM
Post
#30
|
|
Senior Member Group: Members Posts: 2488 Joined: 17-April 05 From: Glasgow, Scotland, UK Member No.: 239 |
Design lesson for future rovers: there should be some simple and reliable mechanism for unclutching a wheel once it is certain that it is inoperable and cannot be recovered. Some kind of pyro mechanism perhaps? tty That's *exactly* how the wheels were organised on the Lunokhods - individual motors which could be popped to allow the wheels to rotate freely if required. Perhaps old lessons should be *remembered*... Bob Shaw -------------------- Remember: Time Flies like the wind - but Fruit Flies like bananas!
|
|
|
Lo-Fi Version | Time is now: 24th September 2024 - 08:00 AM |
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. |