Discrepancy between speed limit between duet 2 and duet 3 mini

[Tricep terry]

Dear All,

Recently I changed my system from a duet 2 wifi towards a duet 3 mini wifi.
In this process, I observed a strange behaviour in the max speed limit of the duet 3 mini wifi.

I use very small movements and very low speeds and configured it therefore a bit differently than usual use cases.

For example:
my M92 commands use 1.00 as a step/mm (while the actual steps/mm is 1600) and have adjusted the M566 and M203 accordingly.
sending 1600 steps therefore creates a movement of 1mm and 16000 mm /min will perform this move in 6 seconds, 32000 in 3 seconds, and all these speeds are perfectly performed on the duet 2 wifi and duet 3 mini when send from a gcode file or via the send box in the duet wifi web control interface.

But now comes the strange phenomenon.

During homing, the duet wifi 2 works as intended and correctly moves according to the requested speeds, the duet 3 mini, does not....

therefore the following homing file only works for the duet 2 wifi:

M400
M913 A70 ; drop motor current to 70%
M400 G91; relative positioning
G1 H2 A15000 F480000 ; lift A relative to current position
G1 H1 A-70000 F480000 ; move quickly to A axis endstop and stop there (first pass)
G1 H2 A15000 F480000 ; go back a few mm
G1 H1 A-70000 F480000 ; move slowly to A axis endstop once more (second pass)
G90 ; absolute positioning
M400
M913 A100 ; return current to 100%
M400

while the duet 3 mini 5 plus comes nowhere nere the requested speeds and I had to change the homing file significantly:

M400
M569 P0.0 D3
M569 P0.0 V10
M201 A100000.000
M913 A70 ; drop motor current to 70%
M915 P0 S-10 R0 F0 H400
M566 A120000.00
M400 G91; relative positioning
G1 H1 A-320 F4800000
G4 P100
M400
G1 H1 A500000 F4800000 ; move quickly to A axis endstop and stop there (first pass)
G90 ; absolute positioning
M400
M913 A100 ; return current to 100%
M569 P0.0 V2000 H2000
M400

Initially, I though these issue was there because of the difference in drivers and stealhchop vs spread cycle mode. The speed and acceleration in this script are still not what it should be, but the homing worked now, although much much slower.

I accepted this, but today, I encountered a new problem, around the same phenomena. I wanted to move one of the linear actuator while the other one was moving in a script. I came up with using baby stepping to to this. However, during baby stepping, the movement again becomes much much slower than it should have been (while sending the same movement speeds manually goes without problems, so I assume no step/pulses or clock issues.

At the moment I found a work around, by configuring the axis temporary to "normal" settings so to M92 16000 mm/min etc performing the moves using baby stepping.

However, It is a very interesting phenomenon that might not be easily spotted. Which I think should be addressed.

Kind regards,

[Tricep terry]

Also after start up, sending a G91 G1 X10000 command does not move the axis at the max speed set in the config file, but sending for example G91 G1 X10000 F500000 will perform just fine (F500000) set as the max speed

[dc42]

@Tricep-terry are both Duets running the same firmware version? Which version(s)?

[Tricep terry]

@dc4 I they were running in different versions (duet 3 mini running on versions RepRapFirmware for Duet 3 Mini 5+ version 3.4.0) and duet 2 wifi running on version 3.3.

I downgraded the duet 3 mini to version 3.3, but it had the same outcome. I also noticed that when up or downgrading software, I've to reinstall the wifi server manually with M997 S1 via YAT to be able to restart the wifi correctly using M552 S2. Previously, this was never necessary and it's a bit inconvenient.

But back to the original issue, even in older firmware versions I've never seen or observed the issue on the duet wifis. So I doubt it has to do something with the firmware version but rather with some processing of the speeds specifically for the duet 3 mini.

[T3P3Tony]

@Tricep-terry please can you do me a favour and test both with RRF 3.4.5

[T3P3Tony]

@Tricep-terry please also give the full config.g files for each board. @droftarts is going to try an recreate the issue.

[droftarts]

@Tricep-terry said in Discrepancy between speed limit between duet 2 and duet 3 mini:

Also after start up, sending a G91 G1 X10000 command does not move the axis at the max speed set in the config file, but sending for example G91 G1 X10000 F500000 will perform just fine (F500000) set as the max speed

RepRapFirmware doesn't use the max speed set by M203 for moves immediately after config.g has run at start up; it uses a default speed. I think the default speed is 3000mm/min / 50mm/s. The speed for the Machine movement buttons in DWC is specified on Settings > Machine-Specific.

Ian