
Curiosity rover writes Morse Code of JPL everywhere it goes - jgrahamc
http://blog.jgc.org/2012/08/curiosity-rover-writes-morse-code-of.html
======
ck2
I was surprised the treads are not very deep on the wheels.

With a 14-22 minute ping time, it better be able to handle most situations on
its own...

~~~
mturmon
They have very detailed physics-based models of terrain-wheel interaction
("terramechanics" is the general term). The tread depth must be one of the
design parameters.

Slip is something they watch closely, and 100% slip is something they worry
about a lot. I worked on a project using a small prototype in that same yard
(metal wheels with metal tread) and was really f-ing hard to get the thing to
slip with anything like a reasonable load and slope.

------
simias
Why don't they just put a camera filming downwards to determine the ground
speed? Wouldn't it be simpler and more reliable?

~~~
vasco
As I understood it that's exactly what the camera is doing, and the morse code
is just a helpful pattern with a known distance to make more precise
measurements of ground speed.

With no patterns one could think of a situation where the surface sand/terrain
would be displaced but your actual position was exactly the same.

~~~
mturmon
All true. JPL has been a world leader in development of visual odometry
("VO"), which is key to estimating slip, which in turn is key to not getting
stuck in sand.

The method hinges on establishing correspondence between visual features in
before/after images. Then, since you know (through stereo ranging) how far
away things are in both images, you can match points and see how far you've
gone. This works better the more visual features (tiny edges and corners) you
have to cue off of, and presumably these treads are generating more
distinguishable features. They ran VO on Spirit and Opportunity, and they will
on Curiousity as well.

A summary is in the first page of this little white paper:

[http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4053.p...](http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4053.pdf)

and one full description is here:

[http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.104....](http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.104.3110)

The good thing is that VO requires no extra hardware, because you already have
stereo cameras.

By the way, they do make commercial velocity sensors of the kind described in
the GP comment (special camera looking down):

<http://www.corrsys-datron.com/optical_sensors.htm>

These may not use VO, they might just use optical correlation. Sometimes
they're used in robotics.

~~~
altarelli
_Sometimes they're used_ ...in optical mice. By the millions.

------
dolson
It should have been DEI.

