Homing fails every other time G28 is entered

jvbiondo

Hello all, thanks to the community helping with my questions.

I am testing a newly built delta for CNC use that has no heated bed or extruder. I have microswitches at top of travel for homing, baud rate is 115000.

From the Arduino IDE, on reset the serial response is:

start

Info:PowerUp

Info:Resetting Z correction

Free RAM:80104

Autoretract:0

X:0.00 Y:0.00 Z:0.000 E:0.0000

SelectExtruder:0

FlowMultiply:100

On the first G28 command I enter the machine homes as expected and responds:

ok 0

busy:processing

SelectExtruder:0

FlowMultiply:100

X:0.00 Y:0.00 Z:328.840 E:0.0000

When I enter a second G28 command I enter the machine doesn't home or move at all and responds:

ok 0

RequestPause:Homing failed!

SelectExtruder:0

FlowMultiply:100

X:0.00 Y:0.00 Z:328.840 E:0.0000

When I enter a third G28 command I enter the machine homes and responds as expected:

ok 0

SelectExtruder:0

FlowMultiply:100

X:0.00 Y:0.00 Z:328.840 E:0.0000

This goes on as long as I enter G28 commands.

If I check the endstop condition prior to entering the G28 command it is always on the endstops after the first home:
endstops hit: x_max:H y_max:H z_max:H Z-probe state:L 

Of course I only anticipate homing the machine once prior to each use, but this behavior does not seem normal, any thoughts?

Repetier

You need to tell firmware to move back z after homing 10-20mm for deltas. At top you have no move place so even adjusting to rotation or tool position will trigger end stops. So if you go down after homing you can adjust without triggering and since end stops are not triggered homing will work every time.

jvbiondo

Repetier said:

You need to tell firmware to move back z after homing 10-20mm for deltas. At top you have no move place so even adjusting to rotation or tool position will trigger end stops. So if you go down after homing you can adjust without triggering and since end stops are not triggered homing will work every time.

Thank you for the explanation, though I still find it odd that it homes correctly every other time even though it is on the end stops prior to homing every time. But yes, it always homes if I back it down first.