Move until step is lost.

My understanding is that the new drivers on the Duet Wifi are capable of detecting when a step is lost. Would is be possible to implement a G1 modifier say S3 that would move the specified axis until a step is lost. This would be useful for endstop free homing.

Are you thinking you'd set the current such that it doesn't destroy itself when it crashes, but holds reasonably well during prints?

That sounds like it would put a lot more wear on the printer over time, and trying to adjust it properly would be more trouble than it's worth. Spending $5 on endstops from China might be easier.

Of course, I would like to see if this could even be implemented just for the sake of experimentation, and skip step detection has other uses too. I just can't see this becoming practical.

Disclaimer - I'm by no means starting an argument. Debating is just how I like to have discussions.

I once experimented with endstop-free homing on my delta. I used M906 to reduce the motor current in the homedelta.g file, then drove the 3 motors far enough so that they were guaranteed to reach the end stops. Then lowered the head a little and restored the current to normal. Homing in this way was only accurate to within 4 full steps, but that was less than 1mm and running auto delta calibration using the Z probe could correct for that.

On the Duet WiFi it should be possible to use the skipped step detection to stop the motor early, but the position uncertainty would still be about one full step.

Btw it's possible to eliminate the homing switch on the X axis of a Cartesian printer by using an IR sensor as both the Z probe and the X endstop detector, as the Ormerod does.

Edited 1 time(s). Last edit at 10/01/2016 02:54AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].