Microstep resolution - why not 16x all the time?

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zenwebb
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Microstep resolution - why not 16x all the time?

Post by zenwebb » Sat Mar 02, 2013 9:34 pm

I'm curious, the wiki assumes 8x microstepping on the X and Y axes, and 2x on the Z axis, but why is that? I'm using the BuildLog stepper shield, and it can be configured for 16x microstepping on all axes. Why wouldn't you want to have the electronics set up for the highest available resolution?
Jason Webb
Grad studen, creative technologist, OSHW engineer
http://jason-webb.info

cvoinescu
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Re: Microstep resolution - why not 16x all the time?

Post by cvoinescu » Sat Mar 02, 2013 10:54 pm

That's because Inventables sells the grblShield, which is limited to 8x. The lower, 2x multiplier on Z comes from a limitation of GRBL, which will force the X and Y to move slower if the Z would exceed the maximum stepping frequency if it went at the same speed. Since Z is screw driven and needs many more steps per unit than the X and Y, one way to circumvent this limitation is to use a smaller multiplier on Z.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

aldenhart
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Re: Microstep resolution - why not 16x all the time?

Post by aldenhart » Sun Mar 03, 2013 1:51 pm

The other reason is that as the microsteps goes up you lose power (torque). This has to do with the fact that there is less time for the current to flow and saturate the inductive motor windings. It also has to do with the fact that the step rates available from grbl will max out at high speeds at higher uSteps. This is mostly an issue for the Z axis.

Setting microsteps is therefore a compromise between a higher value for smoother operation, and a lower value for more power.

Alden

(Full disclosure - we make and sell the grblshield)

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