Delta Question about delta radius vs. arm radius calibration

Hi,

I was just thinking about designing/printing a new effector for my delta, when I realised, that a different sized effector (for example a bigger one with longer magnet to magnet distance) will change my arm_radius.

Precisely measuring this new arm radius can be tricky, so I wondered, if this can be calculated by the smoothieware calibration routines (I have a bltouch sensor installed).
In the z probe delta calibration guide, there is a note that says: “this calibrates the endstops and delta radius only”.

But if you scroll down on that page to “configuration options” it says:

leveling-strategy.delta-calibration.enable         true         
Set to true to enable the delta calibration levelling strategy. This uses the probe to figure out the plane's tilt and arm's radius in a delta machine

So it this simply two different phrases describing the same thing?
I thought arm_radius and arm_length are the two crucial values, that should be put in manually and need to be correct as possible, so the calibration routine can change endstops+printer radius (or delta radius, as wording seems to change between firmwares) for getting the bed level as flat as poissble.
Can the arm_radius be calculated, or only be measured manually?

Best regards,
Benny

Imported from wikidot

You want to give your arm length as precisely as you can, then calibration will work with that to adjust the other things and make it all work.

Thanks Arthur, that’s great.