Multi stepping

[irving2008]

Thanks Irving2008 goes some of the way but still not clear how reproducible partial steps are when under load as the bit I read on the web inferred that steps between full and half were hit and miss not that I fully understand but I would think that as one of the coils only has partial power then its actual position will be influenced by the load.
So I would think that greater accuracy could be achieved with gearing albeit with a slower responding unit being as I want to make fairly small parts I think I should have gone with gearing instead of direct drive, only time will tell.

Peter

As long as you are not overloading the motor the accuracy should be reproducible - how good that will be will depend on the tolerance you can sustain. The tolerance of the motor is about 2 - 5% typically.

As you say, a lot depends on the design and work area of the overall system. With a 200step/rev motor on a 5mm leadscrew, say, 1 full step = 0.025mm. If you wanted 0.01mm accuracy you could either use 1/8 stepping to give .003125mm/step or geardown 2.5:1. The 1/8 step would give positioning of 0, .009375, .021875, .03125, .040625, etc, a maximum error of 0.001875mm, which may be good enough. 1/16 step would halve that error.

The disadvantage as you point out is that gearing down would reduce the ability to do rapids. In the above example at 1000 (full)steps/sec the rapids for the direct drive would be 25mm/sec (1.5m/min), whereas with the geared drive it would be only 10mm/sec (0.6m/min) which makes a big difference on a 1000 x 600 work area. On a 200mm x 100mm PCB router tho its not such an issue.