A stall would result in a dramatic change in the current signature on the motor would it not? Something that would almost certainly flag up a drive fault.


Have we ever heard of a motor stalling, but the drive continuing regardless? I know that Spirit was using a cautious automatic system to recover from stalls within a sol, but for a drive motor to stall on Opportunity and yet the rover carry on driving would be highly unusual.#

I think we're just seing something of an NPE (Near Purgatory Event)

Note, in FredK's image - the 100% perfect track's just outside the churned material. The Front and Rear wheels have similar track width, but the middle wheels are slightly inboard of that. That clear track mark infers the FL wheel turning normally at that time.

Maybe its some soil properties experiment??

But then the latest update does say the right middle wheel has elevated current.

Agreed. And a Navcam from Sol 2220 suggests that the right Front and Rear wheels were turning and tracking normally and the right Middle wheel started to drag. The right Front wheel then began to churn and veer off to one side, as shown
on the attached annotated NavCam.

Nothing on Scott Maxwell's blog yet.

--Bill

It's pretty clear what's happened when you look at this navcam frame:
http://qt.exploratorium.edu/mars/opportuni...0M1.JPG?sol2220
As Doug said, the middle wheel tracks are normally inwards of the front and rear, as at the top of that navcam frame. Then presumably about a third of the way from the bottom of that frame, the RM wheel started to dig in (stall?), forming a trench (edit - dashed blue in Bill's pic). Then the RF wheel slipped into that trench, so it's track moved inwards a bit to line up with the RM track (dashed yellow in Bill's pic). Then the RR (not FL as Doug said) track was visible outwards of the trench (red in Bill's pic).

The more I think about this the more I lean on the side of a regular embedding event. As I pointed out above, the RM trench isn't perfectly smooth. But also, if the RM stalled outright, I might've expected Oppy to yaw around counterclockwise as her right side was slowed by the dead wheel. But there's no sign of that. Also, I might've expected furrows of soil piled up along either side of the RM track, like with Spirit's RF. Again, no clear sign of that.

We'll find out soon enough...

Edit - thanks for the nice illustration, Bill!

Very impressive Bill.

New images down:

http://qt.exploratorium.edu/mars/opportuni...00P1214R0M1.JPG

There's clearly some degree of sinking on the right side as well, so it does look more like a soil composition change rather than a wheel problem on the left side--good news if true!


(Naughty Nprev. Inline image turned into link - ADMIN)

EDIT: Oops, sorry! (Now I finally understand exactly how that works...)

IIRC, when Spirit's RF wheel failed on the way to McCool hill (sol 781) the drive didn't finished immediately but continued enough time to make a long trench.

Now waiting for some official (or "leaked" ) news.

Spirit's right front wheel failed on sol 779, the trench was created following tests to determine the nature of the fault.


http://marsrovers.jpl.nasa.gov/mission/sta...006.html#sol778

I see what appear to be two cleat marks in the image fredk posted, the one nearest the wheel partially buried by soil dropped by the right rear wheel.

Discuss...

Soil mechanics experiment to combine with the previous study of driving cross-ripple that they did. That's my guess.

You do the Hokey Cokey...

Yep, Phil, that's what it's all about...

What are you guys referring to? If you mean the little wiggle in the tracks about 1/3 down from the horizon in that navcam image, that's just the small turn in place at the end of the sol 2218 drive:
http://qt.exploratorium.edu/mars/opportuni...0M1.JPG?sol2218

Was this a new trouble free drive then? How far Algernon?

No, just a picture looking backwards taken from the current site.