Front wheel on Mars rover stops

http://news.bbc.co.uk/1/hi/sci/tech/4821294.stm

On Sun, 19 Mar 2006 10:13:14 +0000 (UTC), "SJP"
wrote:

http://news.bbc.co.uk/1/hi/sci/tech/4821294.stm

they done really well to last as long as they have

In article , Clive
wrote:

On Sun, 19 Mar 2006 10:13:14 +0000 (UTC), "SJP"
wrote:

http://news.bbc.co.uk/1/hi/sci/tech/4821294.stm

they done really well to last as long as they have

Just when you need a KwikFit you can never find one!

"SJP" wrote in message
...
http://news.bbc.co.uk/1/hi/sci/tech/4821294.stm


Have to admit I am surprised they used brushed motors - surely it would be
better to go with motors with only 1 moving part and no consumables?!

Scott

"SC" wrote:

Have to admit I am surprised they used brushed motors - surely
it would be better to go with motors with only 1 moving part and
no consumables?!

MER had a tight schedule, and had to use off-the-shelf components
wherever possible. Whilst brushless-DC motors have been used
successfully by many space missions, such a motor has never been
operated on the surface of Mars. MER neither had the time or money
to develop the first qualified brushless motor for Mars, so they used the
heritage of Pathfinder and MPL, both of which used brush motors.

Whilst brushless motors are more reliable and have very long lifetimes,
they are more complex, requiring extra electronics. Brush motors,
in contrast, are lightweight, with simple mechanical commutation, and
provide higher power-to-weight ratios. The graphite brushes that MER
use tested at over 100 million revs with no failures.

"Ed Holden" wrote in message
...

"SC" wrote:

Have to admit I am surprised they used brushed motors - surely
it would be better to go with motors with only 1 moving part and
no consumables?!

MER had a tight schedule, and had to use off-the-shelf components
wherever possible. Whilst brushless-DC motors have been used
successfully by many space missions, such a motor has never been
operated on the surface of Mars. MER neither had the time or money
to develop the first qualified brushless motor for Mars, so they used
the
heritage of Pathfinder and MPL, both of which used brush motors.

Whilst brushless motors are more reliable and have very long lifetimes,
they are more complex, requiring extra electronics. Brush motors,
in contrast, are lightweight, with simple mechanical commutation, and
provide higher power-to-weight ratios. The graphite brushes that MER
use tested at over 100 million revs with no failures.
I'd also suspect that the problem is actually the bearings at the output
shaft, rather than the motor itself. This is where the dust will have been
gently eroding, and wrking it's way 'in'...

Best Wishes

SC wrote:

Have to admit I am surprised they used brushed motors - surely it would be
better to go with motors with only 1 moving part and no consumables?!

The parts have survived way, way beyond their design life. Brushless DC
drives have a lot more components to go wrong - just not mechanical
ones. A brushless drive has THREE moving parts - the rotor and 2
bearings BTW.

Steve

On Mon, 20 Mar 2006 22:55:47 +0000, Steven wrote:

In article , Clive
wrote:

On Sun, 19 Mar 2006 10:13:14 +0000 (UTC), "SJP"
wrote:

http://news.bbc.co.uk/1/hi/sci/tech/4821294.stm

they done really well to last as long as they have

Just when you need a KwikFit you can never find one!

yeah dont think the AA or RAC will travel that far either