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Beyond Lewis and Clark Gap, Sol 4482- (September 2, 2016-)
hendric
post Jun 16 2017, 07:31 PM
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I'm sure Paolo would do the least risky attempts first, and only the more risky ones after a risk analysis or simulation done on the Test Bed. Perching on a rock shouldn't be too dangerous (I'm not talking a rock the size of the wheel, just one large enough that the force is localized on the tire - so maybe 1/4 wheel height), but trying to drag the wheel across I agree could be dangerous. But since everything can be done with small stepper motor steps, it's not like the drivers are going to gun the engine the first try. The Test Bed can tell us if it's even possible to move the wheel sideways across a rock, it might not work geometrically. Again, I'm not saying pin the wheel to the rock, just let the friction naturally grab and release the wheel as it goes over the rock.

I'm also curious about the Test Bed drive distance vs the rovers because the dust in the Martian environment might be similar to the Lunar dust that gave the Apollo astronauts such fits because it was so fine, dry, and abrasive. Could be that dust is reaching the gearbox or actuator? There might be something to learn about gaskets for future rovers - magnets to keep dust away from actuators or something, like this article proposed for Lunar dust. https://www.sciencedaily.com/releases/2008/...80924191552.htm Perhaps for future requirements a lunar dust analog endurance test could be done against actuators to determine how well they can keep the dust from eroding the gaskets and reaching the actuators.


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serpens
post Jun 16 2017, 11:03 PM
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The recent conversation on the Opportunity General Health includes a pretty thorough Paolo overview of the situation with respect to drive motors and actuators. Well worth the read for any that haven't seen it. For a system designed for a mission success criteria of 90 sols and 700 metres the performance of the mobility systems has been outstanding and I think that the engineering team can sit back and bask in the plaudits of we mere mortals.
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marsophile
post Jun 17 2017, 02:58 AM
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QUOTE (fredk @ Jun 14 2017, 06:48 AM) *
I don't see any real sign of an overhang, just a shadow - compare with this view:
http://merpublic.s3.amazonaws.com/oss/merb...KPP2596L2M_.JPG

Indeed there are rocks in shadow. They show up best (but still faint) in blue light.
Two-D images can give a misleading perspective. Here is a parallel-eye 3D.
(From Sol 4761 images brightened to show detail.)

Attached Image


For those who prefer Xeye, here it is:

Attached Image


Xeye underestimates depth perception for distant objects (but is better for close objects).
Here is a comparison with the image Fredk pointed to (bottom image).

Attached Image


The new (top) image is from a slightly lower angle.

This R1 from Sol 4759, where the rocks are illuminated, tells a different story.
Attached Image

It looks like it was just shadows as Fredk said.
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RoverDriver
post Jun 17 2017, 07:14 AM
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I'm not sure this thread is the most appropriate one for this discussion, I will let the admins move or delete the offending post(s).

After the initial tests I'm not sure we know where the problem is, whether it is close to the motor, or the wheel. I would say that only after we have a reasonable idea we will come up with a solution (if it exists).

All the suggestions so far are good but unfortunately we have pretty severe restrictions due to power and volatile storage (cold and hot temperature testing). We also have to get ready for Conjunction and Winter 8 while providing meaningful means to explore Perseverance Valley.

I don't think anyone has kept track of the odometer on the testbeds but I would be surprised if it was a significant percentage of either Oppy or even Spirit. We typically use it to do small-motion tests (a few meters at most) and the tether is pretty short.

The torque at the output of the gearbox is so strong that any attempt to force a stall by manually locking a wheel was fruitless. So on the one hand we would need to apply a very strong force to do anything significant, and on the other hand one could cause more damage. So if you won't see us try more crazy things, please understand that we rather drive a crippled vehicle than a lander.

Not sure what flavor of lemonade we will make this time (maybe Orange Crush?), but we thought it was almost impossible to use the IDD after Joint 1 became unreliable. I'm sure we will learn how to drive this thing (again!). There's still some of us that remember how to drive a-la-Spirit.

Paolo


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marsophile
post Jun 18 2017, 03:56 AM
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I appreciate that safety is paramount, but if the rover ever did need to find a vise-like terrain configuration, it could perhaps create its own by doing a "wheelie" in soft soil, as it has done many times before.
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fredk
post Jun 18 2017, 02:30 PM
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QUOTE (RoverDriver @ Jun 15 2017, 03:39 PM) *
*I* haven't give up hope on that actuator tho.

Indeed we have some motion this morning!
http://merpublic.s3.amazonaws.com/oss/merb...KVP1242R0M_.JPG
http://merpublic.s3.amazonaws.com/oss/merb...KWP1242R0M_.JPG
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RoverDriver
post Jun 18 2017, 05:05 PM
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QUOTE (marsophile @ Jun 17 2017, 07:56 PM) *
I appreciate that safety is paramount, but if the rover ever did need to find a vise-like terrain configuration, it could perhaps create its own by doing a "wheelie" in soft soil, as it has done many times before.


Not sure what you mean. Wheelies to me refer only to extreme bogie positions, so either mid or rear wheels in air while the other is in contact with the surface. Even in these cases, the shift in CG position would not have a significant impact on the front wheel.

Paolo (who is really happy about the LF wheel being straight)


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PDP8E
post Jun 18 2017, 05:45 PM
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here is a GIF of the wheel movement :
Attached Image


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stevesliva
post Jun 19 2017, 10:13 PM
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QUOTE (fredk @ Jun 18 2017, 09:30 AM) *
Indeed we have some motion this morning!


No doubt LATE in the morning. We're into the melodramatic teenage years now.
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fredk
post Jun 22 2017, 02:47 PM
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From Crumpler's latest post:
QUOTE
We have decided to wait outside the valley until solar conjunction is over. Then Opportunity will begin the descent in ernest. That will be around the beginning of August.

And a sketch of a proposed route over the next couple of weeks:
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fredk
post Jun 23 2017, 03:10 PM
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Details of the LF wheel in the latest update:
QUOTE
In addition to attempting to actuate the steering at different voltages in a straightening (toe-in) direction, the team also commanded very small (half degree) actuations in the toe-out direction in between the straightening attempts. While these also stalled, the very last straightening attempt appeared to break free from whatever was impeding it and steered the wheel to straight.

QUOTE
This very good result was tempered by the fact that we still do not know for certain what the cause of the stalls was and whether the problem could reoccur... tank turning and steering will be used wherever possible.

I'm sure they tried this (and many other things) with the RF.
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RoverDriver
post Jun 23 2017, 11:32 PM
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QUOTE (fredk @ Jun 23 2017, 08:10 AM) *
...
I'm sure they tried this (and many other things) with the RF.


Testing on Mars was quite limited instead. There was much discussion but given the small toe-in value of the RF helped in settling into the decision not to use that actuator again.

Paolo


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Disclaimer: all opinions, ideas and information included here are my own,and should not be intended to represent opinion or policy of my employer.
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