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Direct drive turns out to be the bestSaturday, March 14. 2009
In which your narrator finds that simplest is best...
Going from a 3/8-16 lead screw to a 1/4-20 dropped the inertia of the lead screw by 80%.  A bit of sticky tape on the end of the 1/4-20 lead screw gave me a very firm connection with the surplus Airpax stepper and enabled me to run meaningful thrust exercises with it. I discovered that it was possible to get 250 pps out of the stepper in this configuration. Further, at that rotational rate I was getting 4-5 lbs of thrust, considerably more than the Haydon linear steppers are giving me now on Tommelise 2.0. That translates into a touch over 13 mm/sec axis speed. I'm done fooling with this. T3 is going to use a direct drive powered by old Airpax tin can steppers. $150 in parts, here I come. :-D Trackbacks
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If inertia is your limiting factor, rather than frictional load, then you should be able to go a lot faster with some acceleration.
It introduces some distortion when extruding, but no harm for extruder off moves. They are well worth speeding up because they reduce stringing.
I'm using a one step acceleration/deceleration to get that 13 mm/sec. Flat out gets me right at 10 mm/sec.
When I put the thing in an interrupt loop instead of using millisecond wait commands which don't have a lot of resolution, I suspect that I can push it up to 15-16 mm/sec. Using both axes flat out I should be able to do infil at 20 mm/sec.
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