Question on delta movement and coordinates

I used to have a delta and sold it, so I do not know a way to find an answer to this question, short of buying another and I would like to not buy any more.

Here is the question say you are at a point 50mm above the bed. Now you want to go straight/perpendicular to the bed - down. Can you simply subtract 20 from Z and move 20mm closer to the bed?

I am trying to find out if I can move strictly vertical up/down by changing just the Z or it it means all xyz change

Thanks
Bruce

To move the effector of a delta printer vertically, you have to move all 3 motors by the same amount. So to move it 20mm down, you need to drive all 3 carriages down 20mm.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
To move the effector of a delta printer vertically, you have to move all 3 motors by the same amount. So to move it 20mm down, you need to drive all 3 carriages down 20mm.

Correct if you do not support towers which are not perpendicular to bed (and parallel to each other).

It depends on your definitions of x,y, and z. If you're defining them as the towers, then all three must move. If you're defining them as Z=vertical movement, X= left/right, and Y=front/back, then only Z moves. Smoothieware uses the later definition.

If the towers are not parallel to each other then there is no single Z direction along towers. I.e. straight 20 mm Z move up cannot be done by simply adding 20 mm to tower coordinates.

Anyway, hardly any firmware supports such a situation.The fact that n9jcv needed to ask this at all means that the most simple answer should be good enough for him.
And if he is interested in a more complicated situations then he should check Deriving cartesian->delta transformation equations or he should check a specific implementation of them in e.g. this C++ template named computeTowerCoordinate.

First answer was what I was needing. Thanks all