After main assembly, add rubber bands to each arm one at a time until you can push the effector to any location in the print volume and when release the effector will return home. (top dead center) After you have installed the rubber bands run your fishing line. Loop the line back and forth until you have a mechanical advantage that will work for all positions in the build volume. (I will post more details as I build baby Simpson.)
I will be adding parametric OpenSCAD files as I get time so there can be many Simpson variants out there.
Before First Run:
Load the firmware of your choice. Calibrate all motors so that the change in effective distance of an arm matches what the host software sends.
Edit parameters.py to match you machine. Run zero.py to get calibration routine. Use the gauge.stl to measure all the offsets. Place these offsets in the calibration array in parameters.py.
User whatever slicer program you want. The middle of the bed is 0,0,0. Run the produced gcode through segmitize.py to transform the coordinate system. You may need to do a few dry runs are you modify offset in parameters.py.
This is all very rough. Let me know if something is wrong.
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