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Linux robots



On Tue, 22 Feb 2005 markw at mohawksoft.com wrote:

> I'm building a Linux based mobile robot. I started my career as an EE
> (wow, 20 years ago!), but now I do mainly software.
> 
> I have a Mini-ITX motherboard, wireless network, gellcell battery, LCD
> screen, a rudimentary wheeled base (not great, but a starting point),
> Veleman 8000 digital/analog I/O system, and a dual H-Bridge MOSFET motor
> amplifier.
> 
> I'm at the stage where it boots and can move on its own power. It ain't
> pretty yet, but hey its fun.

Way cool!  Does the flamethrower work yet?
Any chance of pictures?

> How would you guys do wheel rotation feedback? I need to monitor how much
> the wheels move so I can calculate rough position and control velocity. I
> have a couple LEDs and photodiodes installed on the wheels that produce a
> good set of square waves, not perfectly square, but close to a
> "quadrature" encoder. I'm not sure of the resolution yet, but I'll measure
> that later.
> 
> Do you guys know of a good/cheap/easy updown counter system? I can build,
> but would rather buy a kit or something. (I've done my share of
> wirewrapping)

Yes.  Rip open a $5 serial mouse and use its encoder.  I've seen this
outlined in an old Circuit Cellar article, though I doubt I still have it.  
You should get pulses at the mouse's 300DPI.  You might even be able to 
just mount the mouse pushing up against your wheel without modifications.

> Do you think I could hook it up to the printer port and read it fast
> enough. (I know that question relies on wheel RPM and resolution, but they
> are not too fast and the resolution is fairly slow.)

If you have a serial port it would be simpler, especially if you're using 
a mouse as above.  But using the parallel port should work fast enough, 
since I've heard of lighting systems doing that.  You only have (ISTR) two 
input pins, though, so make sure you use them wisely.

-------------------------------------------------------------------
DDDD   David Kramer                   http://thekramers.net
DK KD
DKK D  Football is not a contact sport; it is a collision sport.
DK KD  Dancing is a contact sport.              --Vince Lombardi
DDDD




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