Duet 3 SCARA questions

[jstevewhite]

@JoergS5

Here's homedistal.g

G91 ; relative movement
G1 H1 Y-200 F2000 ; move distal joint counter-clockwise until triggers
G1 H2 Y10 ; back off 10 degrees
G1 H1 Y-20 F1200
;G1 H2 Y20
G90

and homeproximal.g

G91 ; relative movement
G1 H1 X200 F1200 ; move distal joint counter-clockwise until triggers
G1 H2 X-10 ; back off 10 degrees
G1 H1 X40 F300
;G1 H2 X20
G90

I do not use homeall.g because I can't make it stop throwing an error trying to home z, even though I have no Z axis configured.

[jstevewhite]

There is clearly a problem with the angles I'm using here because no combination I have tried puts 0,0 at the Proximal axis.

[JoergS5]

my post about G92 was wrong, see below

[jstevewhite]

@JoergS5

I'll sure try that tomorrow, but at one point I had it set with the angles correct in M208 for the endstops and it still didn't have 0,0 in the appropriate location.

I'll report back tomorrow

[JoergS5]

my post about G92 was wrong, see below

[jstevewhite]

@JoergS5

Image of robot (drawbot, not printer):

Please disregard the marked angles as other than an indication of the range of motion.

I do not understand this bit:

The crosstalk factors define how much the motors interfere with each other. If they are all zero then it is assumed that the X motor affects only the angle between the proximal arm and the X axis, the Y motor affects only the angle between the distal arm and the X axis (not the proximal-to-distal arm angle as you might expect), and the Z motor affects only the nozzle height. If this is true for your printer, you can omit the C parameter. Otherwise, if the parameter is of the form Caaa:bbb:ccc, then:

aaa is the amount by which the X motor (whose primary function is to control the proximal arm) affects the angle between the distal arm and the proximal arm. For example, if movement of the proximal motor affects the proximal-to-distal joint angle in reverse (so that an X motor movement that causes one degree of proximal arm movement also changes the angle between the distal arm and the X axis by one degree in the opposite direction) then this crosstalk factor is 1.

They seem to contradict one another.

G92 does not seem to set the angle the machine believes the arms are at, but instead appear to affect cartesian co-ordinates:

10/18/2020, 11:37:13 AM	M114
X:16.886 Y:150.000 Z:0.000 E:0.000 E0:0.0 Count 1391 22457 0 Machine 16.886 150.000 0.000 Bed comp 0.000
10/18/2020, 11:37:08 AM	G92 Y150
10/18/2020, 11:37:00 AM	M114
X:16.886 Y:95.766 Z:0.000 E:0.000 E0:0.0 Count 0 24915 0 Machine 16.886 95.766 0.000 Bed comp 0.000

As you can see, G92 Y150 resulted in Y being set to 150 and X being unchanged, but the reported angles change to something else entirely.

[dc42]

@jstevewhite said in Duet 3 SCARA questions:

G92 does not seem to set the angle the machine believes the arms are at, but instead appear to affect cartesian co-ordinates:

That's correct, that is how G92 is defined.

[jstevewhite]

@dc42
Can you clarify the bit I quoted? That's from the duet docs and is very confusing.

Also, any advice since I made this thing left handed?

Ultimately, I've been unable to come up with any combination of reported angles in M669 that result in 0,0 being at the proximal axis. The only even remotely functional settings I've come up with result in 0,0. being way up top and no moves being rectilinear. I made a law of cosines spreadsheet and calculated the angles but there's clearly some rotation here that I don't understand.

[JoergS5]

This post is deleted!

[dc42]

I'm sorry, the documentation was out of date. I have corrected it. It now reads (changed part in italics):

The crosstalk factors define how much the motors interfere with each other. If they are all zero then it is assumed that the X motor affects only the angle between the proximal arm and the X axis, the Y motor affects only the angle between the distal arm and the proximal arm, and the Z motor affects only the nozzle height.