Wheel Trouble, ...down to 5 good wheels? |
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Wheel Trouble, ...down to 5 good wheels? |
 Mar 14 2006, 11:28 PM
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#31
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Newbie  Group: Members Posts: 19 Joined: 17-April 05 From: Zagreb, Croatia Member No.: 240  |
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Mar 14 2006, 11:39 PM
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#32
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Member Group: Admin Posts: 468 Joined: 11-February 04 From: USA Member No.: 21 |
There was a tiny bit of motion between sol 779 and 780, though I'm not sure it is very promising.
 click through for a larger (2x) enlargement of the FHAZ images. The wheel doesn't rotate, and it doesn't change its pointing (steering motor), but it does seem to roll with regard to the suspension which doesn't move. Is that even a commandable motion? We know the wheels can turn and can be pointed (yaw) but can they be rolled? |
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Mar 15 2006, 12:11 AM
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#33
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
That's a very odd motion - at first I thought it might just be a change in lighting, but it's genuine movement.
I've got to give a talk to some students tomorrow that will end with "and here's Spirit's wheel appearing to start falling off" Doug |
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Mar 15 2006, 12:49 AM
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#34
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Senior Member Group: Members Posts: 1636 Joined: 9-May 05 From: Lima, Peru Member No.: 385 |
QUOTE (mars_armer @ Mar 14 2006, 11:37 AM)  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. Would you post the rover wheel in graphical description? I still have no a good idea about its design. By now, I tought that there are four motors for motion: 2 in front and 2 in back and the motor axis is connected to the wheel. The others motor are for turning control which are connected at the top of every four motors: 2 front and 2 back. Isn't that correct? P.D. If that looks so, I think that design is the most elegant but not the most robust. Hope this would provide a good lesson for the next Mars rover : MSL (I am afraid that its wheel design is very similar to MER according to the very generic picture.) Rodolfo |
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Mar 15 2006, 01:06 AM
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#35
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Senior Member Group: Members Posts: 1636 Joined: 9-May 05 From: Lima, Peru Member No.: 385 |
QUOTE (tty @ Mar 14 2006, 12:53 PM) 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 Once time, one of the wheels of my truck was stuck by a small stone (between the brake and wheel) and it started to noise awfully. The only way to get rid off the small stone from the wheel was to use a long screwdriver and hammer. What might be done with MER? As MER goes very slow and I don't think that any small stone would stuck any wheel and the most probably ones would be of dust, grain or sand. The use of any kind of shaking with pyro or anything else is not a good design. The best ones would be the wheels have a very tight seal that neither a water or powder can filter into it. On the other hand, the rover wheel has smaller circunference and its 5 kilometers is like 1,000 km for a off road truck with its big tires (I don't exactly compare the cicunference distance). After that distance, a truck need a chasis wash to flush off the dust and other dirty things and some lubrications in their joints. The MER ones has no such service for more than two years. That is Amen! Rodolfo |
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Mar 15 2006, 01:24 AM
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#36
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 Senior Member Group: Admin Posts: 4763 Joined: 15-March 05 From: Glendale, AZ Member No.: 197 |
QUOTE (slinted @ Mar 14 2006, 11:39 PM) The wheel doesn't rotate, and it doesn't change its pointing (steering motor), but it does seem to roll with regard to the suspension which doesn't move. Interesting. That could be a good sign. It looks like it's torquing against a load, causing the suspension to shift, which would infer something jammed somewhere out of view. That would be a far better situation than a malfunctioning motor. -------------------- If Occam had heard my theory, things would be very different now.
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Mar 15 2006, 04:01 AM
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#37
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Senior Member Group: Members Posts: 2998 Joined: 30-October 04 Member No.: 105 |
Not at all good. Slinted's animated-GIF shows that there is radial motion of the wheel, which suggests to me that a wheel bearing has failed.
--Bill -------------------- |
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Mar 15 2006, 04:33 AM
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#38
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Junior Member Group: Members Posts: 90 Joined: 13-January 05 Member No.: 143 |
Looks like a drive will be attempted on Sol 781 (dragging the right front wheel), after some diagnostics. Goal is to move toward an area ~14m away with a more favorable power situation.
There is no debris in the wheel, but also no explanation yet for the anomaly. |
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Mar 15 2006, 09:49 AM
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#39
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Member Group: Members Posts: 184 Joined: 2-March 06 Member No.: 692 |
QUOTE (tty @ Mar 14 2006, 11:53 AM) 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 In a future mission, how about just blowing off the whole wheel? Pyro wouldn't add much weight. |
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Mar 15 2006, 10:47 AM
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#40
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 Member Group: Members Posts: 147 Joined: 30-June 05 From: Bristol, UK Member No.: 423 |
QUOTE (monty python @ Mar 15 2006, 09:49 AM) In a future mission, how about just blowing off the whole wheel? Pyro wouldn't add much weight. Cheers Monty Now that has my warped sense of humour going  Couldn't have come from a better named contributor  But seriously, that is a good point - if a stuck wheel is an impediment - chop it off! Nick |
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Mar 15 2006, 10:49 AM
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#41
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Senior Member Group: Members Posts: 1870 Joined: 20-February 05 Member No.: 174 |
quote: "I've got a little list..... I'm SURE it won't be missed!"
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Mar 15 2006, 01:57 PM
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#42
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Member Group: Members Posts: 252 Joined: 27-April 05 Member No.: 365 |
Yeah, wheel bearing looks likely to me, or some other 'broken' component besides a motor winding. Does anyone know if the wheels have -any- free movement in a radial direction under normal circumstances?
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Mar 15 2006, 02:16 PM
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#43
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 Member Group: Members Posts: 510 Joined: 17-March 05 From: Southeast Michigan Member No.: 209 |
QUOTE (Ames @ Mar 15 2006, 05:47 AM) But seriously, that is a good point - if a stuck wheel is an impediment - chop it off! It's just a flesh wound!  However, I think we'd run into some problems with balance and stability if a wheel gets blown off. Not so bad on the flats, but I think Spirit would lose her mountain goat abilities. -------------------- --O'Dave
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Mar 15 2006, 06:10 PM
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#44
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Forum Contributor Group: Members Posts: 1372 Joined: 8-February 04 From: North East Florida, USA. Member No.: 11 |
Strange co-incidence......today the front left wheel bearing went kaput on our van, its fixed now though
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Mar 15 2006, 06:48 PM
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#45
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
I gave a talk to some 16-18 y.o. school students today - and I always finish my talks with the most recent image I can get before the talk starts...so today I finished talking about Spirit thus...
"To bring it bang up to date, this image was taken yesterday morning, and shows the front right wheel - the same one that was a temporary problem 600 sols ago, essentially stuck. A major stall of the motor suggest that something might be broken for good inside the mechanics of the wheel - so I'm sad to say that I leave Spirit with the news that yes, one of its wheels might be about to fall off" For a bunch of typical teenagers, they got most of the space related gags, went oOoo at the right anaglyphs, wow at the right pictures - and indeed laughed at the idea of a dodgy wheel falling off. For the Brits ammoungst you, there's a joke about finding a Mars rover up on bricks with 6 missing wheels somewhere in there, with the mission engineers saying something like "I KNEW we shouldnt have had that engineering consultant from Liverpool in to do the job" Doug |
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It looks like no rock to me. 
