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Question on delta movement and coordinates

Posted by n9jcv 
Question on delta movement and coordinates
February 15, 2019 10:11PM
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
Re: Question on delta movement and coordinates
February 16, 2019 02:53AM
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], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Question on delta movement and coordinates
February 16, 2019 06:25AM
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).
Re: Question on delta movement and coordinates
February 17, 2019 01:35AM
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.
Re: Question on delta movement and coordinates
February 17, 2019 05:18AM
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.
Re: Question on delta movement and coordinates
February 17, 2019 11:05AM
First answer was what I was needing. Thanks all
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