Alternative Calibration Approach

[dlang]

I hate to harp on my own postings, but please read the page on accuracy issues

Accuracy Issues

With triangular kinematics you only have two contruction time variables

1. the distance between the motors, which we can measure pretty accurately (down
   to the limits of accuracy of the chain, somewhere around 0.1mm)

2. the distance from the center of the bit to the chains.

As I show in this thread

Calibration pattern for triangular kinematics

I have been mulling over ideas for calibration for triangular kinematics and wanted to run an idea past folks we measure the horizontal distance between motors. we may want to add some check for frame flexibility here. pull the chain snug with low motor power and then ramp up to max power and see if the motors move ‘too much’ (i.e. more than chain sag accounts for) someone with a frame that has a solid beam between the motors should check for chain sag. measure the height of the chain from …

making two marks that are an expected distance from each other in the vertical
center line (and then measuring the expected distance) is enough to calculate
the distance from the center of the bit to the chains to an accuracy of 2x the
accuracy of your measurement (so if you can measure to 1/2mm, your resulting
accuracy is ~1/4mm)

This is if you make one mark in the center, and another one up 500mm

If you were instead to make one down 500mm and the other up 500mm from center,
you would be able to be accurate to ~4x your measurement (so if you can measure
1/2mm, you would be accurate to ~1/8mm)

marks from side to side are not going to be anywhere near accurate until you get
things accurate so that marks up and down the centerline are accurate.

Once you have things so that your marks up and down the centerline are accurate,
everything else is going to be pretty darn close (except for chain sag)

Right now the current calibration isn’t anywhere close to being efficient. It’s

1. guess
2. cut
3. measure horizontal and vertical (which are not independent items)
4. alter your guess based on which was larger horizontal or vertical (with no
   real idea how far to modify your guess)
5. move to a different location on the workspace (which means that the
   errors will show up differently
6. if the difference is ‘too large’, goto 1

It should be

1. move to the center (or close to the center in steps of one tooth so you can
   mark the chains at the center location)
2. make test cuts
3. measure the actual distance between the test cuts
4. calculate the correct values

ready to cut accurately.