[X] My Assistant

[Tesheiner]

Attitude information (e.g. tilt) is obtained from the IMU but wheel slippage needs visual/navcam data. Does visodom work with navcam images pointing opposite to the driving direction?

[bgarlick]

Something just occurred to me (probably occurred to others, but I am too lazy to search the forums).

Given that Oppy has already lost the ability to steer one its wheels (fortunately while it was pointing almost straight ahead!), why does Oppy still perform turns using the steering motors? If one of those motors were to die while a wheel was turned at a high angle it could be curtains for future rover control.

Why not instead point all the wheels forward and turn using a 'skid-steer' approach (ie like a bulldozer or 'bobcat'). Yes the turns would be a bit gross and wide, but who cares, what are you going to bump into out here? This includes the end of drive turns for downlink orienting, etc.

Paolo, is there a reason skid steering is not acceptable or why avoiding skid steering is worth risking a turning motor locking up while turned?

[centsworth_II]

Why not instead point all the wheels forward and turn using a 'skid-steer' approach...

My guess is you would just be trading wear and tear on the motor for perhaps greater wear and tear on other parts. Also the loss of steering control in a region full of sand traps would not be good. Also, energy is at a premium up there and that sounds like an energy intensive way to drive. I bet there are a lot of other good reasons.

[RoverDriver]

I presume that in blind drives the usual "emergency stops" like maximum tilt and wheel slippage are still operating?

That is correct. Tilt, pitch, slip values are all monitored.

Paolo

[RoverDriver]

Attitude information (e.g. tilt) is obtained from the IMU but wheel slippage needs visual/navcam data. Does visodom work with navcam images pointing opposite to the driving direction?

It actually works better when you are driving backwards. In meridiani the featured that VO uses are mostly the tracks. Driving backwards they are just in front of the vehicle. When we drive forwards we have the LGA in the way so we have to point the NAVCAM slightly off from the straight back and therefore see the tracks at an angle and larger distance. It usually works but sometimes it does not.

Paolo

[RoverDriver]

My guess is you would just be trading wear and tear on the motor for perhaps greater wear and tear on other parts. Also the loss of steering control in a region full of sand traps would not be good. Also, energy is at a premium up there and that sounds like an energy intensive way to drive. I bet there are a lot of other good reasons.

Correct. In addition, and this is more for Gusev type of terrain, turning while the wheels are straight, 1/2 of the act as a scoop and is a rock falls into one, as it happened on MER-A 318 (I think), it is a potential wheel hazard. If the rock (we call them potatoes) gets wedged between the wheel and the actuator assembly it might prove difficult to get it out.


Paolo

[Pando]

Well, you are not seeing 160m drives for some time but we have done quite long blind drives. I believe I have done a 120-140m blind once.

I have to admit, it's fun to see that on JPL parking lot...

[HughFromAlice]

Paolo,

Assuming you drove the equivalent (terrain wise and energy wise) to a drive like Sol 1797 - which achieved 111 meters - how far do you think the rover would have travelled with a jammed (please not!!) wheel? That might help all of us here to extrapolate to Oppy's likely future progress if the worst did come to the worst.

All else being equal, do you think we could still get to Endeavour?


Hugh

[RoverDriver]

Paolo,

Assuming you drove the equivalent (terrain wise and energy wise) to a drive like Sol 1797 - which achieved 111 meters - how far do you think the rover would have travelled with a jammed (please not!!) wheel? That might help all of us here to extrapolate to Oppy's likely future progress if the worst did come to the worst.

All else being equal, do you think we could still get to Endeavour?


Hugh

Excelent question to which I have no answer. We gained lots of experience with Spirit in this category and one thing we learned is that the soil type makes a large difference in terms of speed of travel, slopes we can traverse. Meridiani is a totally different soil from Gusev. I could give you a number but the error bar would be larger than the number itself ;-)

Paolo

[HughFromAlice]

I could give you a number but the error bar would be larger than the number itself ;-) Paolo

Thanks Paolo - let's just hope it will be a long while before we need to use those error bars!!!!

[djellison]

Just reading Scott's blog - today, funnily enough - http://marsandme.blogspot.com/2009/02/spirit-sol-48.html - talks about the work required to churn soil, he's comparing the first Spirit trench to Opportunities...

"Opportunity's hole, by contrast, was nearly 10cm deep, and they needed less than half as much energy to dig it. Which would tell me something about the differing soil composition between the two sites, if I were that kind of person.)"

That would bode well for Opportunity (if the floor of Eagle crater is like the rest of Meridiani) - BUT - the dunes may become a worse danger if we're dragging.

Doug

[SFJCody]

Looks like 1806 is another drive sol. Keep going wheels!

[Juramike]

Alright, here's my prediction: Oppy will back on parking lot terrain (Aqua/Green) on May 1.

That's assuming a rate like what we've done from Sol1800 to 1806 and no major pit stops.

[Juramike]

Graphic showing track due S from Sol 1806 position.
(The predicted ickiness of the dune field to the E of Porcupine varies between the different models - the most conservative is shown)

The black box at the end of the arrow shows the approximate location of first Aqua/Blue terrain on this vector.
(All the models agree that this would be "Aqua/Blue" terrain - somewhere between Sol1691 and Sol1693 in difficulty.)

-Mike

[Juramike]

Left turn at some point? Maybe soon?