Dragon Star: a good motor without clutch will always have a large dead torque. They make the engine turn very fast (which is efficient) and through gears they lower the RPM and thereby increase the torque at the wheel.

The rsult is though, that a wheel going the other way around would need a large torque to turn the motor. Indeed probably such a large torque that the wheel would be dragged instead of turned.

So if you're not designing in a clutch, there is little need to have an emergency brake release for the situation Spirit's currently in.

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I understand what your saying, I suppose your right.

Found THIS, it seems that she does have a brake release that would allow it to continue without dragging along.

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Those are steering actuators. When not actively steering, they resist the twisting of the wheel, and don't affect the turning of the wheel.

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I was looking at that in particular.

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OK, but the braking they are referring to seems to be that offered by the resistance of the steering actuators to twisting of the wheels. It's something they can do if a steering actuator fails and they desire a wheel to be free to align itself in the direction it is being dragged.

Anyway...

To the topic -- well not exactly news, but good stuff -- from the Planetary Society Weblog, from Phil Stooke, Some great maps of the Mars Exploration Rovers' progress.

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Phil's a regular over at the Unmanned Space Flight forum, which is a great place to keep up with the rovers and other solar system probes. (Phil's maps actually appeared there first, before Ms. Emily grabbed them for her blog.)

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Your just looking at it the other way I am is all, I see it as saying that disabling the brake is possible, but the result of blowing the fuse means loss of twisting control. But I understand what you mean, I guess the article was written purely is all...but isn't an actuator used to turn the wheels? If so then the term "brake" can not be used here because all that is, is resistance alone, not a brake, a brake resists rotation, and has only that purpose, no other. An actuator forces rotation or lack there of.

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The brake Ericson mentions is a brake in the steering actuator. It actually isn't a brake at all, it uses the steering motor itself, when switched off, as a braking device to prevent the wheel from changing direction. The question now becomes why there is no way to 'blow the fuse' on the driving motor of the wheel. I think (speculation alert!) that this could have been done but the designers didn't think it was worth the trouble, weight and increased complexity. A broken drive motor, like we have now, is never fatal because it can be dragged around quite easily. As long as your not in lose sand, low on solar energy and 27 months into the mission.... A broken steering actuator however, when fixed in a rotated position, actually is a fatal accident because the rover is not capable of dragging a wheel around when it is working as a sand scoop, digging itself in. So, the steering motor was a much higher priority to have a 'blowable' fuse than the driving motor.

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I'd speculate that failure analysis had something to do with it, too. If the steering actuator relay opened unintentionally, you would lose control of twist on a pair of wheels, but you can compensate. If the proposed drive motor relay opened unintentionally you would lose braking on a wheel, which could be fatal to a rover on an incline.

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Maybe, but you would lose only 1/6 of your braking capacity. And besides, turning the steerable wheels to let's say 45 degrees or so after driving makes it unlikely for the rover to slide. Still, I believe when something gives up after nearly 10 times its design lifetime you can only stand up and applause. I don't see any reason to 'improve' anything on these machines.

BTW. They are still very much alife and kicking! I wouldn't be surprised if they lasted another 1 or 2 Earth years.

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Last minute diversion takes Mars rover to safety

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Wow, they made it? Awesome...

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I understand why NASA makes these winter migrations, but I find them kind of funny. Sort of like bringing the herd down from its summer pasture up in the hills, down to the valley for the winter. I can see some astronauts riding Mars horses and Border Collies nipping at the heels of all the little rovers, keeping them moving.

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I don't think the Spirit rover will do lots more traveling in its life. It might go another mile. What they need to do is target some area they want to study inch by inch.

The Opportunity rover has had its share of trouble, but so far the drive-train is doing alright. Hopefully it will get to Victoria crater over the next couple of months, spend a month looking that over for deeper layers, and then hit the road cruising South or West for bigger more interesting terrain.

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Folks on the UMSF are suggesting that Opportunity will go into Victoria and never come out. For one thing, there isn't anything of equivalent geological interest for many kilometers.

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I read that. Maybe it won't come out. They thought it might not come out of Endurance Crater. I'm guessing they will exhaust their interest in Victoria, and give getting out a try, and eventually succeed. How long this will take, and whether the rover survives that long is anyone's guess.

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I think Squyres at one point referred to the possibility of not being able to get out of Endurance as the horrible fate of "being locked in the candy store." Victoria should be the same and then some.

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I think that in Victoria, it will be harder to get close to something like Burns' Cliff. Further, with the grinder mostly dead, and the Mossbauer tool getting weak, there is probably less to do there than in Endurance. On the other hand I agree with Squyres about it being a good place to be stuck.

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I just think it's sad that Spirit has a wheel out of comission

http://www.cnn.com/2006/TECH/space/0....ap/index.html

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