Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

Call me stupid, but what exactly do you adjust to make the gantry square once the whole sequence has finished? What is the purpose of step 4? Do you have separate cotrol of the two X distances in 6?

Hi Kit,

Quick answer, once the sequence is finished the gantry is square.

So the normal single motor home search (used by everything from gbrl on your 3d printer, mach3 and the DDCS) is:
1. Drive axis until home switch activates (at which point you have likely gone past it)
2. Retract axis very slowly until home switch releases (you are now at 'home').

In a setup with two motors one driving each side of the gantry adjust the switches/inductive targets so that when each respective release point is reached the axis is square.

Challenge now is to 'trick' the controller that is executing the single motor home search algo above into locating the point where both switches exactly release.

This is what the logic I described does. Step 4 is required during retraction as when a motor's home switch releases that motor is at 'home', whilst the remaining motor isn't yet there so requires more steps. My board never generates steps, it only suppresses steps if required. So in this case DDCS still believes it needs further retraction so continues to generate retraction steps, however my board only passes these onto the motor that has not yet reached 'home'. When this motor does finally activate it's switch both motors are at 'home' and my board signals this to the DDCS.

If your question was due to believing that because at step 2 both motors have activated their home switch and the DDCS has been signalled meant that the motors were at 'home' then this is not true. It wouldn't work as you may have overshot due to the momentum of the gantry and the angular momentum in the screw and it is highly unlikely the hysteresis of two switches is identical. This is why everyone does the very slow retraction until release which avoids both these problems.

This whole process will re-square a machine that has gone out of square. The machine only goes out of square if a driver misses some steps due to noise, a motor stalls or if someone turned a ballscrew by hand when the machine was off.