Getting Unstuck in West Valley Options

[RoverDriver]

The image was taken as part of the West Valley pan on sol 1367
http://marswatch.astro.cornell.edu/pancam_...WestValley.html
http://marswatch.astro.cornell.edu/pancam_..._L257_pos_5.jpg

Thanks. This exactly the kind of posting I'd like to see. THANK YOU!!

Paolo

[lyford]

Pardon my ignorance, but what does the term "high centered" mean? Is it referring to center of gravity? A 4WD phrase? Both sides are equally dug in???

[nprev]

"High-centered" usually means that the vehicle's center of gravity is being supported on something other than the drive surfaces, so there's little or no traction, Lyford.

Paolo, it's good that there's some significant lateral slope. Are there any transducers or some indirect means to measure how much of Spirit's weight is resting on the wheels? That would be good to know for strategy development.

Based on your description of the situation, if it was me in a truck or something I'd gun it forward, expecting the left wheels to slip & hoping that the right wheels would grab enough to spin me downslope (leftwards) & pick up dual traction again.

[HughFromAlice]

"....risk of high centering the rover," project manager John Callas said. "There is a real danger of it getting permanently stuck."

Purgatory ...looked pretty scary.......wasn't immediately obvious

From one who has been bogged in remote places many times during their driving career, I would say thinking it through and - above all - patience pay high dividends!!! I'm sure that they'll test, retest and reretest....... over many many weeks if necessary.

Paolo, besides getting thermoses of strong black coffee air freighted to your team, is there any small thing at all that UMSFers could do that could be of support? (Like the v useful posts above of exactly where Spirit was bogged - or some thread similar to the Drivability Analysis etc.) Very frustrating to have to just sit here while the wheels spin!!!!

[marsophile]

This is maybe grasping at a straw, but is the soil traction affected by temperature? Is there any reason to think a night move, when it is colder, might have better traction?

[RoverDriver]

"High-centered" usually means that the vehicle's center of gravity is being supported on something other than the drive surfaces, so there's little or no traction, Lyford.

That is correct. Sorry for using terms that are unfamiliar.

Paolo, it's good that there's some significant lateral slope. Are there any transducers or some indirect means to measure how much of Spirit's weight is resting on the wheels? That would be good to know for strategy development.

Not that I know of. The rocker-bogie system since it is passive is an indirect measurement, but it is affected by the mechanical properties of the soil.

Based on your description of the situation, if it was me in a truck or something I'd gun it forward, expecting the left wheels to slip & hoping that the right wheels would grab enough to spin me downslope (leftwards) & pick up dual traction again.

A car or truck is not really representative of the type of motion we have on the rover. It is mostly a sequence of quasi-static moments rather than a dynamic event.

Paolo

[nprev]

Got it; I used the truck analogy for illustration only.

What I was thinking was something like a 30 sec run on all drive wheels (forward or backward!) Even churning the soil on the left side provides some impulse via reaction. If you can get the nose to swing to the left enough, you're probably home free.

[nprev]

Here's another unsolicited silly idea: Can you turn the 3 operable front & back wheels 90 deg with respect to the lateral axis of the rover & try to translate it to the left (not a spin, all driving the same direction)? That might drag you clear of whatever's presumably underneath & reseat the wheels.

[RoverDriver]

Here's another unsolicited silly idea: Can you turn the 3 operable front & back wheels 90 deg with respect to the lateral axis of the rover & try to translate it to the left (not a spin, all driving the same direction)? That might drag you clear of whatever's presumably underneath & reseat the wheels.

Nope. The max is 60deg, we tried to turn them 30deg and drive forward (1894-1899) and made some (slowly diminishing) progress.

Paolo

[SpaceListener]

A question, when MER landed on Mars, its six wheels were kept inside. I wish I would have seen the movie on how MER unstowed their six wheels before rolling out from the lander bag to see whether the below idea would be feasible.

Depending upon to its technical characteristics, is possible to perform stow the 2-4 or 6 wheels until its belly touches on the surface and again perform to unstow the wheels very slow trying to turn around somewhat so that the wheels can pose on better firmness soil?

[Stu]

Roughly, yes. The roll of the rover is not very accuratly represented as well as the precise state of each wheel, but the position itself is quite accurate.

Thanks Paolo, appreciate that. It was just a thrown-together thing, so glad to know I wasn't too far out.

All the best to you and your team as you start looking at this. Hard days ahead of you, to be sure, but you're the guys to get our gal free.

[nprev]

Hmm. How about rocking it? That would be a 60 deg all wheels right short move going aft, followed by 60 deg all wheel left going fwd, repeat a few times & see if her nose begins to point downslope.

(BTW, thanks for your patience with my amateur suggestions, P; you're busy, and your replies are kind, but no worries if you got better things to do! I'll post whacko thoughts as I get them just for fun.)

[BrianL]

Paolo, could you move your seat forward a bit? I don't think nprev has enough legroom back there.

[nprev]

...fortunately, my legs are retractable!

BTW, Paolo, don't forget to adjust your rear-view mirror before backing up!!!

[Guest_Oersted_*]

I wonder if the arm could usefully push against the ground in any way, to take weight off wheels? Would that be helpful? That would obviously be a last-ditch (no pun intended) effort. The arm is pretty strong and the rover weighs less on Mars...