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Do rovers need a specific trenching tool?, Dead wheel works, but designed scoop would be better
Floyd
post Dec 2 2007, 07:46 PM
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The stuck wheel has been key to most of Spirit's most important discoveries. Should future rover designs include a scoop which can be dragged behind the rover to turn over the soil? It could be on an arm with just one motor/degree of freedom--up or down. The scoop/plow could be on a flexible arm so if it snagged a rock, it would deflect away. Since everything on mars is covered with a layer of dust, you need something to continuously trench to find sulfates, silica or the next unexpected thing. The arm could be very light if you had a little scoop/rake at the end of a flexible fiberglass pole. Maybe you could add some type of simple sensor to the scoop to determine the crude spectral properties of the freshly exposed soil. Lots of possibilities.

What do you think--is a scoop/plow/rake a worthwhile rover tool? What is your design?


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mike
post Dec 2 2007, 09:23 PM
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A simpler design would be to have the scoop hanging on the underside of the rover, then it could just drop straight down. As far as it snagging on something, you could just have the software check for some limit on extra friction and stop moving if the force is too high.
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SpaceListener
post Dec 3 2007, 12:56 AM
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My philosophy is that an "Space hand" is of vital importance in order to increase the survival of spacecraft as the main objective and also taking the advantage of its own characteristics.

Let us suppose about the problem of Spirit, the arm would assist to improve the motion. For Opportunity, the arm would help it to go closer to rocks and lower to bottom of Victoria and also to climb on sandy surface. Overcome any accident such as one with more than one month sand stuck to Opportunity. Anyway, this arm would help both rovers to improve the science by snagging any interesting stone, rock, dig the surface, etc.

You can see this example with the Shuttle's own long and powerful arm that help to improve the security and survival of spacecraft.

However, I think that this facility, will lead a much increase the budget to the program since the engineering to build an intelligent arm is very expensive as I know about the Shuttle's arm. Sophisticated software, very light material and strong, more video camera, incorporated laser for measuring the distance, etc., etc.

Finally, it would be a one of the top wishlist for MSL since it can supply electrical power with more prediction. At this point, I cannot further comment about the trade between benefit and costs by incorporating an intelligent arm to MSL project. However, for the philosophy of survival, it must be a "yes" or "yes" choice.
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edstrick
post Dec 3 2007, 05:31 AM
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I have been frustrated the entire MER mission, since before landing, at the lack of any capability to observe the intact stratigraphy of the soils. Yes, Yes, Yes, what would you remove from the MER's to include, blah, blah, blah. But MSL REALLY should have something. ... And ExoMars.

I've thought that a very simple, 1 degree of freedom plow could be very revealing. A simple arm, spring loaded, with a single up-down motor. At the end is some equivalent of a (I think the term maybe moldboard) plow.. essentially a single-sided plow, designed to cut into the surface, leaving a 45 or 60 degree slice-exposed and relatively undisturbed soil slope, and turn-over the soils of the opposing surface. The angle should be less than the angle of repose for loose soils... maybe that's less than 45 deg. (I'm too lazy to google and check)

The plow blade should be sping-loaded-hinged so that if it catches it's leading edge on something that resists too much, it simply pivots to the rear and slides over the whatever.

The whole idea is that this thing would be very light, KISS designed (keep it simple, stupid), with one exception. In case of failure of the lower/raise motor, it should have 1 backup, maybe pyro initiated, forced retraction ability so as to not cause rover mobility problems with an un-retracted plow.
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Shaka
post Dec 3 2007, 06:18 AM
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unsure.gif How deep a furrow?

Edit: This proves it. nprev and I must both be dreaming in lockstep.


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nprev
post Dec 3 2007, 06:18 AM
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Ed, man...take a pill! smile.gif Understand you're bolstering for criticism, but I'm with you; good idea.

Trenching the martian soil clearly is scientifically valuable, which was completely unexpected until Spirit's wheel failure; this will surely be recorded as one of the great incidences of serendipity in modern science.

Your schema sounds very practical, and like the fail-safe mode; well done!


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djellison
post Dec 3 2007, 09:34 AM
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QUOTE (edstrick @ Dec 3 2007, 05:31 AM) *
But MSL REALLY should have something.


Well - it's not going to.

I struggle to see what benefits (when balanced with the addition failure modes, mass, volume, power etc) a simple trenching device would have over the techniquie of lock-5-and-drive-1-wheel. We got some fairly good trenches that way. Having a constant trenching tool would be a complication and a restriction to mobility that I really don't think is necessary. Imagine a turn in place with a plough in the way - or the limitations to WEB clearence that would be incurred. Sorry - I just don't get it - look at the nightmare we have for mobility with 1/5th of the wheels screwed on Spirit. A plough will produce a lot more drag than a locked wheel and I can just see day after day after day of it getting stuck on things and/or breaking off. Springs etc. are not to great at -80 degrees - the metal doesn't really want to play that way.

What Spirit may have shown us is that there is a lot more value in playing scratch-and-sniff than we ever thought possible, so from a planning perspective, it would put in your mind the option to do a little trenching test at the end of every significant drive (the scuff in MER terms). But bolting something on the bottom of a rover to do it - it scares me half to death.

ExoMars is proposing to do this properly - a drill tool.

Doug
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edstrick
post Dec 4 2007, 11:02 AM
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DJEllison: " We got some fairly good trenches that way. "

Sorry. We didn't. We got churned up holes in the ground with practically all tracesof stratigraphy removed.


Nprev: "Trenching the martian soil clearly is scientifically valuable, which was completely unexpected until Spirit's wheel failure"
DJEllison: "What Spirit may have shown us is that there is a lot more value in playing scratch-and-sniff than we ever thought possibl"

We had clear signs from Vikings that there was "interesting" structure in the soils, most specifically "duricrusts" at both landing sites, plus drifts and more indurated soils. Spirit didn't see too much till it reached the hills, but did spot at least one patch of light salts on the long drive southeast, then hit (as I recall) some light salts on the climb to the summit, then hit a major patch of multi-colored salts on the drive south from el Dorado toward Home Plate. The wheel lockup just forced us to see how much interesting geology there was in the soils.

As I argued, a very simple trencher plow, normally kept retracted, AND WITH REDUNDANT RETRACTION CAPABILITY, would do a far better job of slicing a stable, stratigraphy revealing cut in the ground than just grinding your way down with churning treads.
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djellison
post Dec 4 2007, 11:22 AM
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I just don't see it working - I don't see it producing any soil stratigraphic record at all. I see it making a little furrow of mixed soil, in essence no better or worse than spirit's FR wheel.

If you want soil stratigraphy - do a vertical mission - a big arm - Phoenix style, or a drill or even just a more simple sampling tool (Pluto was good on Beagle 2).

Worth investigating - worth doing some tests on - but I don't think it's the right way of doing it and I just can't see it achieving what you want it to.

Doug
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ElkGroveDan
post Dec 4 2007, 04:02 PM
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QUOTE (djellison @ Dec 3 2007, 01:34 AM) *
the technique of lock-5-and-drive-1-wheel.

Don't forget the newly learned technique of lock-1-and-drive-5-wheels smile.gif


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ilbasso
post Dec 4 2007, 04:49 PM
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and don't forget that they were trenching with the wheels before Spirit's got stuck - they were deliberately making wheel trenches in Eagle Crater.


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centsworth_II
post Dec 4 2007, 06:05 PM
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But it was Spirit's stuck wheel that really showed the extent
of what lay unseen just beneath the surface. Some big
discoveries would not have been made but for that wheel.
Just think, as MSL rolls happily along, who will not wonder
on occasion what we're missing.
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hendric
post Dec 4 2007, 07:28 PM
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QUOTE (djellison @ Dec 4 2007, 05:22 AM) *
I just don't see it working - I don't see it producing any soil stratigraphic record at all. I see it making a little furrow of mixed soil, in essence no better or worse than spirit's FR wheel.
Doug


I think that's what he mean by tilting it. Most plows have two halves to make a cut into the ground: \/ (from above looking at the plow)

The StrickPlow (if I understand it correctly) would look more like \ except tilted slightly down so it looks like \, ie it is at a diagonal, but it is also tilted backwards a little bit. The trench wouldn't look like --_-- but more like --^^\__/--, with the removed dirt on the left side, and the slope on the right cut so that the dirt doesn't slide down.

That being said, I agree with the KISS philosophy. Just put a spade-like device on the arm, at the joint that can contact dirt so you can get enough torque to lift a few oz. It's not going to be a rock-thrower or a stuck-in-Purgatory-pusher, but a simple thin blade for moving a 25g or so. Hell, make it out of paper/thin plastic with a slight curve, should be plenty strong for moving dirt/dust and flexible enough not to be a problem.


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algorimancer
post Dec 4 2007, 07:30 PM
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I like the plow idea. However, I did a fair amount of pulling plows with tractors as a teenager. It takes a LOT of force to pull a plow (which is why our neolithic ancestors hitched them to big animals), and I just don't see this amount of force being available. My own experience was with with sandy soil, which was trouble enough. On Mars this would be through regolith with lot's of rocks of many sizes mixed in - it strikes me as a very difficult proposition. On the other hand a simple arm designed for the purpose - perhaps even designed to take advantage of the strength of the wheel motors - seems easily doable.
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Floyd
post Dec 4 2007, 08:00 PM
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algorimancer--It all depends upon the size of the plow as to how hard it is to pull. hendric made that point in a near simultaneous post. I was also thinking small, but such a tool would require some sand/mars box testing to get a design that was not too hard to pull and cleanly turned over 2" -3'' of soil.


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