Let's talk about motion control with an AVR

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Something I have been pondering and tinkering with over the months is precision motion control. I understand PID, trapezoidal velocity profiles, quadrature decoding etc, and I'm not really looking for anyone's valuable trade secrets or specific code snippets. Really I am wondering about what a motion control data structure would "look like" .. for example I think it would be neat to be able to load a waypoint into this structure from your main program loop, say "go" and sit back while everything runs in the background (more or less) transparently.

I wonder, is this how things are done "in the real world"? I've studied some basic motion control code and I see that the user must basically constantly update a waypoint to effect a movement. This seems a little ... backwards to me. I'd rather abstract all of that from the user's point of view, but I don't know if this is a good strategy or not.

Well, I guess I should make this topic at least generally relevant to AVRs. I think the new mega48/88/168 are perfect chips for these duties because of all the pin change interrupts (good for quadrature decoding right?) and higher speed. At any rate, I would appreciate a good shove in the right direction ...

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What litle experience i have had boils down to using a commercial controller card.
The card was a multiple embeded ( this qualifies it for the forumin question) '186 design sitting on the old ISA buss.

Card was programmable via a port( usual hex 300 or thereabouts location) on the buss. Programing language was a script like language written by (usually ) C application.

The user would send data to the C application and the data and motion would then be processed into the script like language and voila..

Everything else was transparent to the user.

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Couple of years ago I saw a blurb in the PSOS newsletter that Varilites in Dallas had a 68000 and a ethernet chip and PSOS in everyone of those computerized lights that they leased to Shoco for concerts. They all knew where they were in 3d space, and a command comes down the net that says 'everybody look at the drummer' and they do it. Polar coordinates and everything. This was at least 10 years ago. Boy its hard to remember way back when if you are over 50.....

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