What type of motor is suitable for a plotter type device?

Steppers are easy to use, and hard to optimize. If you keep them easy they'll be big and power hungry.

DC motors are harder to use and easier to optimize (IMHO). You'll need position feedback, and when you're done you'll know a bunch of interesting control theory. They'll be smaller and less power hungry than unoptimized steppers -- but getting them working initially will be more difficult.

I doubt that you would be able to use the motor that drives the roller

-- it's probably too small to move the head and x assembly along the y.

I guess you could use DC motors, but the construction and troubleshooting would be much more difficult than using steppers. Also, the learning curve might be very steep.

The best advice I can give is to start scrounging -- if you can find some old dot matrix printers (especially ones by TI), you're all set.

The polished rods and the carrier are excellent for y travel, and unlike modern (inkjet) printers, the steppers were usually quite robust. Two of them (one on each side) will surely carry your x assembly with little problem. A nice plus is that all the hardware (belt, cable, or chain along with all pulleys and rollers) is also right there, ready to use as is.

As for z, I'd suggest the stepper from a hard disk drive. Now you have to find a real old one (anything above 25M probably uses a voice coil), but they're invaluable.

Good luck!

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That's the impression that I got from the motor tutorials that I've been reading. I think having an open loop system is not so bad to track the printerhead's position, but it seems like the motor accuracy is about 7 to 15 degrees (verification please?) for the permanent magnet versions. This will probably lead to alignment issues, no?

Learning controls theory would be great. I only had one class of that subject, and I already forgot. :( I need to find a good book on the subject.

I also read that DC motors are load dependent, no? So, I might need a bigger motor to drive the print head and holding rod.

Thanks, Tim!

Do you know of any For Dummies book on DC motors?

Good idea. I usually see a bunch of old printers being given away on Craigslist.

Thanks!

You can get steppers with more steps/revolution than that -- I think 1.8 degrees/step is fairly common, but below that probably gets iffy. Look around.

You can always gear them down, if you can accept the backlash in your gear train.

Did you read my tag line? I have a book for you!

If by "load dependent" you mean "need a bigger one for a heavier load" -- _all_ motors are like that, including steppers.

There's one pitfall I should warn you about: for a long time, my hobby was electronics, and I disassembled obsolete equipment for parts to feed that hobby.

Then one day I suddenly realized that my hobby had actually become tearing apart old stuff, and it had been years since I'd actually used any of the parts for new electronics projects.

Weaning myself off of that and getting back into electronics was as bad as trying to kick an addiction.

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For X, use the motor and carriage that the printer uses for X. Mount it on a frame that you design, which you use ordinary OTS table-moving stuff to move for Y.

Have Fun! Rich