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mars_armer
I hate to be the bearer of bad news, but I just heard that there is a serious problem with Spirit's right front drive actuator after yestersol's drive. (This is the actuator that had high currents in the past and led to the backward-driving strategy.) It will take awhile to evaluate the situation, but early speculation is grim.

In a worst-case scenario, they can still drag the bum wheel along, but don't expect another summit view.

Best-case scenario would be a rock or debris jammed in the wheel.

This is a heads-up, sorry I can't really give more info at this time. I still thought you all would like to know.
Myran
Thank you for the heads up mars_armer.
With winter approaching which would mean lower temperatures, something might have jammed, but just as you say, lets hope its just a splinter of rock that can be wiggled loose.
DFinfrock
QUOTE (mars_armer @ Mar 14 2006, 12:29 AM) *
It will take awhile to evaluate the situation, but early speculation is grim.


The problem is, they can't spend a month trouble-shooting like they did with Oppy at Olympia. Spirit has to make progress toward McCool Hill, and that winter haven. sad.gif

David
Sunspot
You mean the wheel will no longer turn at all anymore?
Shaka
QUOTE (mars_armer @ Mar 13 2006, 02:29 PM) *
I hate to be the bearer of bad news,

daaaaaaaaaaammmmmmmmm sad.gif Thanx, Mars. I'd shoot you but I'm too depressed.
Finger crossing time, Guys! You know it has to happen, but still...
mars_armer
QUOTE (Sunspot @ Mar 13 2006, 05:27 PM) *
You mean the wheel will no longer turn at all anymore?

That's right, it stalled. So far the data is limited, so I may be jumping to conclusions. But based on what I've heard, the most likely interpretation is a failed motor, meaning the right front wheel would be steerable but wouldn't turn.
Jeff7
Yeah, let's really just hope that it's just a rock stuck somewhere. I think something like that happened before.
Either way, they know how to drive the thing in 5-wheel mode, which is good. So spin-round, get to safe ground, then analyze the thing thoroughly.
BruceMoomaw
Do you mean that the wheel won't turn even if its motor drive is disengaged, or just that the motor has failed?
Shaka
QUOTE (BruceMoomaw @ Mar 13 2006, 06:13 PM) *
Do you mean that the wheel won't turn even if its motor drive is disengaged, or just that the motor has failed?

Do we have six clutches on this thing? Can we disengage the motor and free-wheel? huh.gif
BruceMoomaw
Under ordinary circumstances that is possible. In fact, it's what they did when they had the earlier problem with high friction in one of the wheel drives, until they managed to redistribute the lubrication to get the motor working properly again.
CosmicRocker
Oh, no. So that is one reason why Spirit has moved so little recently. It would seem to be an appropriate time to pray to the engineers. It's not likely to be caused by a rock lodged in the wheel, since Spirit has been travelling over a fairly hard surface recently, and the few available hazcams show no suggestion that debris is in the wheel. It is curious though, that there are so few recent hazcams available if there is an issue with that wheel...3 pairs from sol 774, 1 pair from 776, and nothing else so far. Is that due to the MRO/MOI communication? I thought that would be finished by now.

But yes, that seems to be the $64,000 question. Can it still free-wheel as it once did, or is it locked? All I can tell from the images available so far is that Spirit was driving backwards on sol 774 and it left differently appearing left/right tracks. At some point it had turned around 180 degrees, and then it turned back and was in a somewhat different orientatation/location by sol 776.

Even if the wheel is shot, they should be able to drag it to safer ground, but it may take some learning along the way.
djellison
QUOTE (CosmicRocker @ Mar 14 2006, 07:08 AM) *
Oh, no. So that is one reason why Spirit has moved so little recently.


No - read the first post - this is a brand new thing - literally yestersol.

The comparatively little movement recently has been because of the DSN conflict between Spirit and MRO so all commands for Spirit have had to go up via UHF which has a very long lead time - it's like super-restricted sols.

Tosol looks like diag.
QUOTE
780 p0781.03 2 0 0 2 0 4 navcam_1x1_az_324_3_bpp
780 p0981.03 2 0 0 2 0 4 navcam_1x1_az_324_3_bpp
780 p1213.00 2 0 0 2 0 4 ultimate_front_hazcam_3_bpp_pri15
780 p1242.01 1 1 0 0 0 2 front_haz_front_right_wheel_subframe_pri_17
780 p1313.02 2 0 0 2 0 4 rear_haz_ultimate_3bpp_pri15
780 p2138.04 2 0 0 2 1 5 pancam_right_wheel_L27
780 p2138.04 2 0 0 2 1 5 pancam_right_wheel_L27
780 p2600.07 2 2 0 0 2 6 pancam_tau
780 p2630.03 56 2 0 0 2 60 pancam_saw_skysurvey_L4578R2478
781 p1585.00 4 0 4 0 0 8 navcam_cloud_4x1_dwnsmp_RVRAz_calstart

Doug
Bill Harris
Oh well, stuff happens. We're all a lot creakier than we were 30-40 years ago.

My suspicion would be that this is a geartrain failure. I forget the exact reduction ratio, but there many gears and bearings between the motor and the wheel and there has been a failure along the way. Remember, we are many hours past the design service life.

Spirit needs to get to an interesting north-facing site. She may be a 3-legged dog, but we still love her...

--Bill
edstrick
I note that both from Husband hill and from the drive to and around home plate, the driving on the north McCool "flats" and the lower flank of the hill look mostly pretty easy.... likely sand traps are rare and high-density large cobble areas are scarce. Some of that "diagonal" stripe of lighter and grayer colored terrain on McCool are pretty rubbly and cobbly, but they're not in the drive to get onto the hillslope.
Marz
Poor Spirit, just as she regains the lead in milage, she hits another bump in the road.

I suppose there is a plan to return to Homeplate in spring, so I expect the driving around McCool will be very conservative. Maybe if we're lucky, some of the Homeplate unit will be found along the east slopes of McCool.

I was half hoping we could get some closer images of the Chaos terrain that was next on the adjenda, but now I worry it's a rockbed too far.
mars_armer
QUOTE (Shaka @ Mar 13 2006, 09:15 PM) *
Do we have six clutches on this thing? Can we disengage the motor and free-wheel? huh.gif

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.
tty
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
Bill Harris
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
alan
Something in there?
Click to view attachment
Toma B
That's good news...if it got in, it can posibly get out of there...Would not be the first time.
helvick
[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)-->
QUOTE(Toma B @ Mar 14 2006, 08:23 PM) *

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
mars_armer
QUOTE (alan @ Mar 14 2006, 11:49 AM) *
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. unsure.gif
helvick
QUOTE (mars_armer @ Mar 14 2006, 09:34 PM) *
I knew I should keep my virtual mouth shut and wait for more data. unsure.gif

Absolutely not ! If everyone waited until they were certain of what they were saying then we'd have nothing to do here.
Shaka
QUOTE (mars_armer @ Mar 14 2006, 11:34 AM) *
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. unsure.gif

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. blink.gif
helvick
QUOTE (helvick @ Mar 14 2006, 09:46 PM) *
Absolutely not ! If everyone waited until they were certain of what they were saying then we'd have nothing to do here.

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.
Shaka
QUOTE (helvick @ Mar 14 2006, 12:05 PM) *
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)
helvick
QUOTE (Shaka @ Mar 14 2006, 10:34 PM) *
...And the pendulum swings... (Like looking for WMDs)

And finding just dust it would seem. Well time to wait for more news.
Sunspot
I thought it might have been a rock at first... but now i'm thinking it is probably some internal reflection too sad.gif
djellison
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
Bob Shaw
QUOTE (tty @ Mar 14 2006, 05:53 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


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
Daba
QUOTE (helvick @ Mar 14 2006, 11:05 PM) *
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.


sad.gif It looks like no rock to me. sad.gif sad.gif

Daba
slinted
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?
djellison
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
RNeuhaus
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
RNeuhaus
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
ElkGroveDan
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.
Bill Harris
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
mars_armer
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.
monty python
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.
Ames
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 huh.gif

Couldn't have come from a better named contributor laugh.gif

But seriously, that is a good point - if a stuck wheel is an impediment - chop it off!

Nick
edstrick
quote: "I've got a little list..... I'm SURE it won't be missed!"
Burmese
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?
odave
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! smile.gif

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.
MahFL
Strange co-incidence......today the front left wheel bearing went kaput on our van, its fixed now though smile.gif
djellison
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
lyford
QUOTE (monty python @ Mar 15 2006, 01:49 AM) *
In a future mission, how about just blowing off the whole wheel? Pyro wouldn't add much weight.

well, maybe just to blow open the clutch or something so it could freely turn - then dragging it wouldn't be dead weight.
Sunspot
Still limping along:

http://qt.exploratorium.edu/mars/spirit/fo...23P1210R0M1.JPG
Burmese
Good, they aren't going to sit still and spend a week analyzing the problem w/o moving. I suspect they just make best time possible to the slopes and then take a breather to see if they can do anything about it.

No updates from SS since Feb 5th, really could use another one by now.
general
QUOTE (Sunspot @ Mar 15 2006, 08:54 PM) *



Looks like she's returning to Home Plate
Marcel
QUOTE (Sunspot @ Mar 15 2006, 08:54 PM) *

Ohmy...this doesn't look good at all. Let us not forget, that dragging a blocked wheel is no problem in this loose material, but roving around rocks is a must in this situation. If it's really stuck (which is most certainly the case because of the high gear ratio indeed), rocks that could be driven over before are an obstacle now: draging along rocks isn't easy on 5 working wheels.

It might get us some interesting views under rocks though....something we did not see before ! I remember thread that was about turning rocks with the arm ! And: we'll get a loooong trench ! ALWAYS look at the bright side of life (I am trying to keep the corners of my mouth up !)

I hope this motor starts working again. I remember something about a gear ratio well within hundreds: this means it is going to be hard to force the motor back and forth by excerting force on the wheel itself. It might be done in combination with a high current boost through the actuator, while pushing the wheel to a stationairy surface (large, coarse rock, with the "cleats" of the wheel pushed on it): the other 5 might slip then.... unsure.gif unsure.gif

Fingers crossed that they'll fix it....like they did before. That wasn't a complete stall however...it was a higher current, but still turning.
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