Linux robots

[markw at mohawksoft.com (markw at mohawksoft.com)]

> 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?

Flamethrower? It's not that sort of robot. :)
Pictures, sure, I'll get the digital camera out and snap a few.
>
>> 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.

Hmm, that has some interesting prospects I hadn't considered. The one
problem I have is that I need two: I have a diametrically opposed wheel
setup.

I very much like the idea of an interrupt driven and kernel buffered
system that I don't have to write or debug. If I rip apart the mouse, I
could use an axis for each wheel and the buttons for contact sensors. I
could use select to wait on the serial port. Since the encoders are read
at the same time, maybe the relational movement will also be more
accurate.

I need to think about this, it is a very good concept. Very good inded.
Thanks.


>
>> 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.

Actually, you have a lot of pins on the parallel port that can be read.

http://www.mohawksoft.com/techtips/parport.html