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Stepper direction on Delta's

Posted by VectorRoll 
Stepper direction on Delta's
April 20, 2017 12:59PM
This is just a query.

In the Marlin Firmware it specifically says that DELTA does not invert for the stepper direction.
// Invert the stepper direction. Change (or reverse the motor connector) if an axis goes the wrong way.
#define INVERT_X_DIR true // DELTA does not invert
#define INVERT_Y_DIR true
#define INVERT_Z_DIR true

Is there a specific reason as to why that is?

I ask because in tweaking my Kossel Mini to try and get a little larger Printable_Radius I found that that my carriage placement and movement range sort of cuts it down. You see I have a Linear Rail version of the Kossel Mini and the instructions say to to place the rails at a certain distance. With the rails being a certain length the carriages do not go down as far as the pulley versions. My Printable_Radius is more like 80mm so a 160mm diameter. 200mm diameter is what I want and what it should be. So in looking at how it is setup I have two options. I could lower the rails or just invert the carriages. Inverting the carriages would be a lot easier as I have already gone through the process of leveling and squaring everything. But if I do that I need to Invert the directions of the steppers as the belts would also have to flip. Yet the Marlin Firmware specifically says that DELTA's do not invert. So I am wondering why that is.
Will it cause adverse affects in how things are printed if I do invert them?
Re: Stepper direction on Delta's
April 20, 2017 03:19PM
I find it very surprising that Marlin doesn't let you invert the motor direction when it is configured for a delta. But you can just reverse the motor connectors instead.

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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Stepper direction on Delta's
April 21, 2017 12:47AM
When I was running Marlin, my config had this:

#define INVERT_X_DIR false // DELTA does not invert
#define INVERT_Y_DIR false
#define INVERT_Z_DIR false

which is opposite to yours. So I'd say that it's fine to adjust this value.
Re: Stepper direction on Delta's
April 23, 2017 12:03AM
Thanks for the input both of you. I went ahead and tested out changing the value and it does seem to work fine.
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