Thread: Confused about stepper sizing
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22-09-2017 #1
Hi
My mechanical build is almost complete 20mm HiWin rails and bearings on X & Y axes with 2010 lead screws X axis is 1500mm and Y axes are 1000mm. Total weight of my gantry including the spindle is around 40Kg and I've been trying to calculate what size motors I need for my axes, but both my own calculations, and the output from several online motor calculators are giving me results that I wasn't expecting.
For example on the Y axis with a total load of 40Kg and a cutting force of 5N my total required torque @ 80 rpm (800mm/min) is coming out with a figure of around 0.18Nm, this would easily be achievable with the 175oz Nema 23 stepper on the openbuilds store which should put out around 0.7 Nm @ 48v and 80 rpm.
My gut instinct was to go for motors in the 400+ oz range, which seems to be what everybody recommends for this sort of size machine. Are my torque calculations way off or is there another reason that I need to massively overspec my motors?Last edited by Jeff; 22-09-2017 at 01:49 PM.
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22-09-2017 #2
Hi Jeff and welcome to the forum. In my opinion I would go with nema 23 3.1Nm from cnc4you and get AM882 drives from China and run them at 68V with a toroidal transformer power supply.
..Clive
The more you know, The better you know, How little you know
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22-09-2017 #3
Hi Clive, I had looked at the motors from cnc4you before I confused myself with my calculations. I think I know where I stuffed it up I was getting confused about feed rates inches/m vs mm/m the speeds I used in my calculations are way too low. I'll do them again at around 10000mm/min and see where that leads me :)
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22-09-2017 #4
Yeah that was where I was going wrong :). The 4Nm motors from cnc4you will give me cutting speeds of around 3000 mm/min and rapids around 10000 mm/min (which is as high as I can go due to the critical speed of the ballscrew), on a 48v supply with a 3x margin. 68V is way above the ideal voltage for these motors (3.0mH inductance) so I think I'll stick with 48V rather than turn my motors into workshop heaters :)
I'll probably get the CWD556 DSP drivers from there too.
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22-09-2017 #5
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22-09-2017 #668V is way above the ideal voltage for these motors
If you'll be cutting wood, you'll quickly find out that 3m/min is quite slow.Gerry
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29-09-2017 #7
I'm using the same motors, am882 drivers and a 68v psu. Got the motors running at 12500mm/min at first testing.
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