3d delta printer, convert tower vertical position to xyz in space

[Dr_Doggy]

My new printer! has 3 vertical towers with rods at length D , which come together to form a position in xyz space.

Any one happen to know the equation it uses to figure this out?

 

[Tony Stewart]

The vector length , D of each rod, depends on the RMS difference in each axis.
So D=√{(X-Xo)²+(Y-Yo)²+(Z-Zo)²}.
For base Bo at location Xo,Yo,Zo

 

[Dr_Doggy]

I am very glad you mentioned about the RMS, actually the reason i ask was cause i was told one of my diagonal rods is bad length, I dont believe this is so , since i sized them while threaded through screw. but he is still probably right. I also used a spread sheet to log results for the G29 code, the best result showed a 0.3mm difference across the z-tower axis in the bed at the corners, but ok in center, like a u shape, however it is not a convex/concave error since the perpendicular axis' are ok aswell . I can post graphical later if it helps.

is there a way we can break down the D value to each RMS value, so i can tune for a size difference in the towers?

 

[Tony Stewart]

only by offset from some reference calibrations , such as corner and middle test calibration with some object.

If your actuator has stiction, there may be hysteresis error.
If stressed in a static position, there may be geometric bias (offset) in some places more than others.
If couplers or sleeve bearings have wobble, then other errors can occur including hystereis.

 

[Dr_Doggy]

I have induction probe that returns the offset value of the true bed - nozzle distance when z should = 0, at multiple points across the bed.
if I understand that , would it help to get a second bed on stilts(level) that would measure the same values but at a higher point in z? it would be simple enough for me to modify code to do this..