Older blog entries for marcin (starting at number 3)

After getting all excited about the possibilities of software subsumption, I have made a very basic simulator using Borland C++ Builder (ie for windows) V1. You can find it on my geocities site under the news section.

While I wasn't able to achieve everything as easily as I hoped, I think there is heaps of potential here, without necessarily totally exhausting my ability to comprehend what's going on. The hardest part can be the arbiter on the outputs - currently it is a winner takes all arbiter - if a more cooperative approach to resources is desired. So now I'm going to try to stick this into my robot on the weekend - this will be a bit of a challenge since I still have to write the driver for the IR ranger and rewrite the motor control code, but it's all getting pretty exciting now, so I guess I'll just have to forgo sleep.

Cheers, Marcin

20 Jul 2005 (updated 20 Jul 2005 at 07:15 UTC) »

I am totally ignoring the ultrasonic rangefinder at the moment in order to limit the exponential increase in complexity. I figure if I make the code modular and therefore pluggable, I'll either be able to add a module (ie driver) for the SRF or if I'm out of I/O then I won't. A smart design will, however, hopefully mean that there will be a bit of I/O to be had.

I've had a read of Chris Schur's PAAMI (http://www.schursastrophotography.com/robotics/paami_main. html) and predecessor and I do like the concept, although being pretty useless with a soldering iron I'm going to try the software path to subsumption. I figure that with my M16C running at 24MHz, (PLLx2) I'll be able to do some serious almost-parralelism. In the future, though, I would like to try doing some hardware subsumption - I have a motorola HC08 C compiler so it may be a goer (they are pretty cheap too, for the little ones). Then again, I have that Philips ARM able to do 32-bits at 60MHz and heaps of code space and RAM that may tempt me instead.

I am beginning to think, having considered it some more since my last post, that the best way to achieve the asynchronous FSM that Chris talks about, but in software, is to totally run via interrupts. So rather than a while (1) loop and a big nested case statement in the main(), I think that maybe all state transitions are handled by dedicated ISRs. It goes against the short and lean ISR theory, but when you think about it, it is a type of co- operative multi-tasking that subsumes all ISRs/responses below it. Then, once the response is complete, control by the ISR is released and the next lower ISR (which was interrupted) will be given a go. A lot will depend on how many levels of interrupt I can get.

Once I rewrite the basic bits (ie basic control actions), I'll post on the success or otherwise of this theory.

Does anyone else have a view on this? Can responses be given here in a post/reply type forum?

Oh yes, and did I mention that I get really jealous of all these people who have well kitted-out workshops and can make their own wheels, and chassis, etc? Well, I am. Making stuff yourself is fun, if you have the tools and know how to use them.

Cheers, Marcin

So I got my GP2d02 and SRF04 sensors today, nice. But it seems I need to get a little bit smarter with my use of timers. The M16C has 8 (including 5 PWMs) but with 4xPWM for the DC motors, 1xPWM for the sensor-spinning servo, at least 1 (maybe 2) timers/event counters for the GP2, and I haven't looked at the SRF yet, or future encoders on wheels ... I think I need a redesign.

I know I can halve the PWMs for the motors with the use of a couple of gates - I hate to increase the component count but there may be no option - I'd like to have the ability to control the pwm to each motor independently, hence I need at least 2 PWMs.

This redesing is probably a good time to look at implementing a better structured FSM and maybe some element of subsumption (although I hear it may be hard in software).

I wonder if anyone uses neural nets in mobile robots?

Cheers, Marcin.

18 Jul 2005 (updated 18 Jul 2005 at 06:00 UTC) »

I currently have a blog on Blogger (sydbot.blogspot.com) but I think this is a better place for it.

Does anyone know if there is a robotics club in Sydney?

This is my first post, and I'll post details of my adventures into robotics here.

Basically, I have made a base, which is now going to get some sensors mounted onto it - a Sharp IR ranger for collision avoidance, and a SRF04 ultrasonic ranger for mapping/localisation. The SRF04 will be on an oscillating servo to provide a scan similar to radar on war ships. We'll see how it goes. Initially, I'll be using the Renesas M16C 16 bit uC until it becomes apparent that I need more grunt - in which case I have a Philips 2138 32- bit ARM uC ready to go.

My sensors arrived today in the mail (yet to get home and open the box) so we'll see how it goes.

Cheers, Marcin

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