PolarGraph addition to my Wall Mounted Pen Plotter

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Kinematics

FluidNC has config settings for WallPlotter kinematics. There is very little documentation and it is not “supported”, but it does seem to work OK. Here is how you set it up…

kinematics
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Refer to the above diagram (not drawn to scale) for an example of my setup. The dashed black line is the drawing area. The circles in the top left and right are the pulleys. I wanted the machine home (x0, y0) to be bottom left - refer to the blue lines in the diagram. The red lines are an example of machine home in the center. Here is the kinematics section of config.yaml:

MACHINE HOME: BOTTOM LEFT

kinematics: 
  WallPlotter: 
    left_axis: 0
    left_anchor_x: -80.000000
    left_anchor_y: 902.000000
    right_axis: 1
    right_anchor_x: 845.000000
    right_anchor_y: 902.000000
    segment_length: 1.000000

If you wanted the machine home to be in the center of your canvas (red lines) it would look like this:

MACHINE HOME: CENTER

kinematics: 
  WallPlotter: 
    left_axis: 0
    left_anchor_x: -462.500000
    left_anchor_y: 492.000000
    right_axis: 1
    right_anchor_x: 462.500000
    right_anchor_y: 492.000000
    segment_length: 1.000000

Notes:

  • All measurements are made from the “anchor points” on the pulleys. If you use the center of the pulleys, the geometry will be a little off. I use the 2 o’clock position on the left pulley and 10 o’clock position on the right. See this post Steps per mm (Wallplotter kinematics) for a discussion.
  • In my example the pulleys are symmetric in relation to the drawing area, but technically they don’t have to be. One can be horizontally offset more than the other. They do have to be at the same height however.
  • It is important that the gondola is as close as possible to the home position described in the kinematics section when it is at machine x0, y0. More discussion on that in a later post.
  • My pulley offsets are 80mm from the canvas sides and 82mm from the top. Technically they can be 0 and 0 but that would not work very well. I’d shoot for 100mm and 100mm if you have the space.
  • Default segment_length is 5. The lower the number, the smoother the curves but you sacrifice speed. I have it set at 1.
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