G20 and G21 affect interpretation of rotary axis angles

[dc42]

See https://forum.duet3d.com/topic/38754/rotational-a-axis-affected-by-g20-g21. Currently, when G20 is in effect all distance units get converted from inches to mm even when they refer to rotational axes.

[dc42]

Currently, when G20 is in effect, movement units in G0/1/2/3 commands are always converted from inches to mm when they are fetched from the parameters. We'll need to check whether the exis is rotational and only do the conversion if it is not.

This potentially also affects the interpretation of the G1 F parameter. This will currently always be converted, however if only rotational axes are moving then it should not be.

[dc42]

Provisional fix implemented in 3.6-dev. There is however a remaining issue, which is partly due to a logical problem with the whole idea of G20/G21. Consider the following:, where axis A is rotational:

G20
G1 X10 F100
G1 A10
...
G1 A10 F100
G1 X10

The F parameter will be converted in the context of the current command, so in the first block the F100 parameter will be converted from inches, which is correct for the G1 X10 command but not for the G1 A10 command. Likewise in the second case the F100 parameter will not be converted, so the G1 A10 command will be executed at 100deg/sec but thew G1 X10 command will be executed at 100mm/sec.

It's unlikely that the same F value would be required for both a linear and a rotational movement, so this case may not be realistic. A more realistic one is this:

G20
G1 F100
G1 A10

In this case there is no context to the F100 parameter. Currently RRF will assume that no rotational movement is involved, so it will be converted from inches. This is not correct if the following command is rotational.

To fix this we would need to just store the F parameter and delay interpreting it until a movement command with no F parameter is encountered. This is perhaps best combined with #1113.

[dc42]

Fixed the remaining issue described above. A side effect of this fix is that the value reported in object model field inputs[N].feedrate is now the raw value specified whereas previously it was the value specified converted from inches/min to mm/min if G20 was in effect.

[T3P3]

User is reporting the issue fixed for G0 and G1 but not G2 and G3

[dc42]

G2/G3 issue fixed in source code, needs testing.

[dc42]

No response from the user, so closed as believed fixed.