Opitical Mouse for tracking robotic movement

Someone posted a URL with a picture of a bot they were helping high school
kids build in the past few months.  It used an optical mouse.  But instead
of using it to track ground movement, they used it to track the wheel
movement as a cheap shaft encoder.  The wheel was large enough that they
simply placed a sheet of paper against the wheel and mounted the mouse
against the wheel looking at the paper (if I am remembering correctly)).  I
don't remember the name to Google for.  Maybe the guy that posted will read
your post and answer or maybe someone else here will remember who it was?

I don't know how accurate the mice are however.  They don't need to be
accurate to work as a mouse since you have constant feedback with the user.
They might have more error than your stepper and wheel slipping combined.

--
Curt Welch                                            http://CurtWelch.Com/
curt@kcwc.com                                        http://NewsReader.Com/

Ah, I was able to find it with a bit of google work.

Here's a video news report about the bot ...

http://video.google.com/videoplay?docid 65197422869440629

And here's an article about it:

http://www.linuxjournal.com/article/9103

Both talk about how they used the optical mouse.

--
Curt Welch                                            http://CurtWelch.Com/
curt@kcwc.com                                        http://NewsReader.Com/

I would've thought that the scroll wheel encoder would be easier to use
(that's what they're made for aren't they?)

The above project used a standard PC board running Linux which means it
already had support for a standard mouse.  It was probably easier for them
to use that than to interface some type of encoder.

But sure, in general, shaft encoders are easy and cheap to build and would
probably be more accurate than the mouse.

--
Curt Welch                                            http://CurtWelch.Com/
curt@kcwc.com                                        http://NewsReader.Com/

Agilent (HP) makes the sensors (i don't know of other vendors) and you can
find data sheets here;

http://www.avagotech.com/products/document-results.jsp?catIdI39

one example is;
http://www.avagotech.com/assets/downloadDocument.do?idA5

some points to note - maximum speeds top out at about 14 inches/sec, and if
sensing ground, depth of focus is typ 0.5mm.