Monday, February 05, 2007

 

Dual Darlingtons operational on the new Tommelise controller board...

I decided that I needed to build a new controller board largely because the one I'd already built was more patches than board. Those patches were confusing me and requiring more patches, so I took a few days off to build another board.



All that's left to do is put the power transistor that controls the heated extruder barrel and a bunch of two pole connectors to collect the sensor interrupts for limits and shaft encoders.

Comments:
Forrest, what circuit are you using there? Looks like a big processor there, not a tiny little pic. Is that for 1 axis?
 
That's a PIC 18F4610 and it controls the whole shooting match. It costs about $9-10 and it lets me run my system with one controller board which is as you see it plus one power transistor to run the extruder heating element, four two pole connectors to take in sensor inputs and one two pole connector to shoot amperage to the extruder heating element.

The 4610 also lets you do direct USB comms instead of having to have a MAX232 comms board to convert PIC serial comms into something your PC can understand. I haven't got around to making that work yet, though.

Because Adrian, Vik and the rest of the conventional RepRap team had pretty much already got their token ring with four controller boards attached approach working I decided that RepRap would be better served if I tried to do some higher risk developments that could, if successful, be used in the next generation RepRap. That's why I'm using shaft encoder feedback gearmotors instead of steppers and a single board, big PIC approach to control.
 
I think one larger controller board for the cartesian engine makes a lot of sense. After all its not all that much I/O and the number of axis is fairly stable at 3. The complexity of synchronising movements over a serial network is avoided. It might be sensible to keep a network of slaves for the head(s) as this seems the most variable part of the evolution.

I think that will be the approach I take with my RepStrap effort, but probably not a PIC.
 
Yeah, I've thought of a separate controller for the Mk 2.1 as well, but not for just right now. It is, as you say, very good sense if you have multiple extruder heads.
 
Why did you choose shaft encoded motors over stepper motors? Do find one easier to program or physically control?

I'm also curious to know what you program in and if you have your subroutines based on interrupts/hardcoded order or a full-fledged RTOS.
 
"Why did you choose shaft encoded motors over stepper motors? Do find one easier to program or physically control?"

Steppers were already being done by everybody else, so I decided to see if I could get shaft encoded gear motors to work. They're potentially a lot cheaper than steppers and are energetically a lot more efficient. You get much more bang for your buck.

Because you're not using so much power the controller boards are easier and cheaper to build, though the coding is considerably more complicated.

"I'm also curious to know what you program in and if you have your subroutines based on interrupts/hardcoded order or a full-fledged RTOS."

I'm using the Oshonsoft IDE with a BASIC compiler. It's cheap, reliable and Vlad takes quality control very personally.

I'm doing interrupt programming.
 
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