Archive for May 3rd, 2011

Thing-O-Matic: Stepper Motor Torture Test

The G-Code in BenJackson’s Smooth Motion test does a good job of identifying mechanical constraints and stepper motor problems. Even after doing all the rod alignments and sundry tweaks, my TOM wasn’t reliable around 4000 mm/min = 65 mm/s and had terrible mechanical resonances around 5000 mm/min. While normal extrusion feeds run around 30 to 40 mm/s (1800 to 2400 mm/min), I didn’t have a warm fuzzy feeling that everything was operating correctly and, in fact, the TOM suffered the occasional missed step.

The per-axis speeds in thingomatic.xml limit the maximum speed attainable in the G-Code; you can set the F value in the G-Code as high as you like, but the axis won’t move any faster than it’s allowed. I think ReplicatorG applies those limits when it converts human-readable G-Code into binary Sanguino3G code.

After installing the new Y axis stepper motor and X rod follower, I ran through another series of tests to see what was new & different. With all the mechanical binding eliminated and a decent Y motor at 800 mA, the TOM now traverses reliably up to about 5500 mm/min = 90 mm/s. The X axis loses steps dependably by 6000 mm/min = 100 mm/s with the current set to 300 mA.

Note that this is not printing, just moving. Printing requires attention to a whole bunch of details, but first you gotta have reliable motor control.

So I set the upper limit at 5000 mm/min and we’re both perfectly happy. Indeed, with the new Y axis motor, the mechanical resonances have vanished and it’s a much quieter machine at the normal speeds. As a confidence builder, that one will suffice for now.

I have a 34 mm NEMA 17 in hand to replace the X axis motor; it’ll be all good.

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