Wheel Trouble, ...down to 5 good wheels? Options

[mars_armer]

Do we have six clutches on this thing? Can we disengage the motor and free-wheel?

The short answer: I'm 99% sure the answer is "no".

The long answer: There are two things that resist turning of the wheel when the motor isn't energized: dynamic braking and static detents. Dynamic braking occurs from back-emf in the motor electrical circuit, and provides a resistive torque when the wheel is turned but no force when the wheel is stopped. Dynamic braking can be disengaged in the electrical system. The static detents, on the other hand, are magnets that cause the motor to preferentially stay at certain turn positions. These are necessary to keep the wheels from rolling after the rover comes to a stop, and cannot be disengaged. Because of the high gear ratio of the drive gearbox, it takes a hefty torque to the wheel from the outside to overcome the detent.

Bottom line: assuming the motor stall can't be corrected, they will probably have to drive backwards dragging a stuck RF wheel. This is something they have done before in the West Spur area when they were afraid the RF motor was nearing end of life. Though at that time, I think they periodically turned the RF wheel a bit to drive over the buildup of dirt in front of the wheel.

[tty]

Design lesson for future rovers: there should be some simple and reliable mechanism for unclutching a wheel once it is certain that it is inoperable and cannot be recovered. Some kind of pyro mechanism perhaps?

tty

[Bill Harris]

there should be some simple and reliable mechanism for unclutching a wheel...

Probably not do-able within the constraints of 'simple and reliable'. Given that the original service life of the Rovers was 90 days and they have lasted a long time, the optimum solution would be to upgrade the motor and geartrain to give a much much longer service life.

--Bill

[alan]

Something in there?

[Toma B]

That's good news...if it got in, it can posibly get out of there...Would not be the first time.

[helvick]

[quote name='alan' post='45573' date='Mar 14 2006, 07:49 PM']
Something in there?
[/quote]
Looks like a rock stuck in there to me. With some stretching and bending of the luminosity curves there seems to be a fairly irregular potato shaped object jammed in there.

If it is a rock is there any chance that it could be jolted loose with some creative driving?

B)-->

That's good news...if it got in, it can posibly get out of there...Would not be the first time.
[/quote]

The last one that I recall was
this one from Sol 345

[mars_armer]

Something in there?

That's really encouraging!

Now I think (hope) I overreacted to the initial description I heard of the problem. At that time it sounded like there was evidence in the telemetry that the motor circuit had failed "open", which suggested a broken wire or brush inside the motor. By comparison, unsticking a rock sounds easy.

I knew I should keep my virtual mouth shut and wait for more data.

[helvick]

I knew I should keep my virtual mouth shut and wait for more data.

Absolutely not ! If everyone waited until they were certain of what they were saying then we'd have nothing to do here.

[Shaka]

That's really encouraging!

Now I think (hope) I overreacted to the initial description I heard of the problem. At that time it sounded like there was evidence in the telemetry that the motor circuit had failed "open", which suggested a broken wire or brush inside the motor. By comparison, unsticking a rock sounds easy.

I knew I should keep my virtual mouth shut and wait for more data.

I hope that's a rock too, but none of it is out in the light looking clearly 'rocky'. I hate to suggest it might just be some internal reflection - like my...er...flying saucer.

[helvick]

Absolutely not ! If everyone waited until they were certain of what they were saying then we'd have nothing to do here.

And just in case we get too optimistic:
Example 1
Example 2

There's shading in both of these in exactly the same place and the lighting is from a similar direction.

[Shaka]

And just in case we get too optimistic:
Example 1
Example 2

There's shading in both of these in exactly the same place and the lighting is from a similar direction.

...And the pendulum swings... http://static.flickr.com/36/112580016_7b9d7405a1_o.jpg
Somebody in another forum doing some more intensive photoenhancement.
(Like looking for WMDs)

[helvick]

...And the pendulum swings... (Like looking for WMDs)

And finding just dust it would seem. Well time to wait for more news.

[Guest_Sunspot_*]

I thought it might have been a rock at first... but now i'm thinking it is probably some internal reflection too

[djellison]

At a first look - it just looks like dust to me - and the two sets of diagnostic images ( one presumes before and after a commanded rotation of the wheel ) show no change in the position of the wheel

Doug

[Bob Shaw]

Design lesson for future rovers: there should be some simple and reliable mechanism for unclutching a wheel once it is certain that it is inoperable and cannot be recovered. Some kind of pyro mechanism perhaps?

tty

That's *exactly* how the wheels were organised on the Lunokhods - individual motors which could be popped to allow the wheels to rotate freely if required.

Perhaps old lessons should be *remembered*...

Bob Shaw