Re: Homing in Marlin

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revwarguy
The G28 command is implemented in Marlin.cpp starting at line 996. There is conditional code for Deltas there, since it needs to home up all three axes at once. To do this, it sets the feedrate at 1.732 times the nominal homing feedrate with no comment. (What is that about - i.e., why the hard-coded weird number 1.732?)

It is about sqrt(3). So it is possible that author somehow thought that sin(60°) or cos(30°) should be involved. But I do not have a clue why.

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revwarguy
Also, it sets the max length of travel until switch trigger at 3 times Z_MAX_LENGTH (why so much - isn't 1.1 already more than what is possible?)

1.1*Z_MAX_LENGTH is not not enough but Z_MAX_LENGTH+DELTA_DIAGONAL_ROD would be enough if the printer is already callibrated. The best value would be FLOAT_MAX/k where k is a safety factor which would be determined based on the planner code so that no overflow can happen.

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revwarguy
It then calls a routine called endstops_hit_on_purpose() which I couldn't find anywhere to see what that does.

It is in stepper.cpp. It just clears flags that endstops were hit.
This way the code indicates that the endstop hit was processed at the higher levels.

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revwarguy
I must have a problem since I do not see the back-off occurring.

Probably, I do not use LCD so I'm not sure it calls the same homing code.