G38 acting different on Toolboard 1LC then on Duet 3 Mainboard.

j.dewit · 4 Jun 2020, 10:37

I have recently switched my prototype to use 1LC toolboards, as this will reduce wiring complexity due to the size of the machine.

I am running into a problem that the G38 probe command is working different on the Toolboard then when connected on the Duet 3 mainboard.

I am using firmware version 3.1.1 on a Duet 3 with SBC.
I have 2 toolboards connected on addresses 20 and 21. Running 3.1.0 firmware.

We are using the G38 probe command to perform a movement that halts when a sensor is triggered. (It is a sort of locking mechanism.)

The config used:

M558 P8 C"!21.io0.in" H0 F500 T3000   ;

And the command used to perform the movement:

G38.2 F500 Y50  ;

Y is always homed at 0, 0 is minimum and 50 is max.

Both movements work, and stop when the sensor is triggered. But on the Mainboard, the current Y position is the actual amount moved (For example 35). On the Toolboard this is always the target position of 50, even if it only moves to 30.

This is causing a problem when returning Y to 0, as on the toolboard we are trying to go to '-20'. Since it it thinking is it at 50. And end up stalling the motor since the end of the possible movement of the axis is reached. The only way to correct this misalignment is by re-homing the Y axis.

On the mainboard this problem does not occur, and we are using the amount moved to check if the locking mechanism is working since it needs a minimum amount of travel.

Could this be a Bug related to the Toolboard, or is this a limitation of the Toolboard?

j.dewit · 4 Jun 2020, 11:41

Have just connected the probe sensor to the mainboard, and the result is the same.

Some more information:

The working situation: Y motor connected to mainboard, Y endstop for homing connected to mainboard, and Y probe connected to mainboard.

Not working scenarios:

1 Y motor on toolboard, Y endstop on toolboard, Y probe on toolboard.
2 Y motor on toolboard, Y endstop on toolboard, Y probe on mainboard.

Next is to test some scenario's with the motor on the mainboard, and sensors on toolboard.

dc42 · 4 Jun 2020, 13:02

Before you do many more tests, please be aware of this fromhttps://duet3d.dozuki.com/Wiki/Duet_3_firmware_configuration_limitations:

Endstop switches connected to the main board cannot control motors on an expansion board. This is planned to be fixed in release 3.2.0.

Although it doesn't say so, the same applies to Z probes.

j.dewit · 6 Apr 2020, 13:12

I was aware of the endstops, good to know that the same applies to probes.

And I did some more testing. I don't think that the problem is related to where the sensors (endstops/probes) are connected. They seem to always work. Even the probe works when controlling the motor on the toolboard. It is just not returning the right atual position after probing.

The motor(Y) and zprobe are connected to the mainboard. And the endstop(Y) to the toolboard. Then everything works.
Homing works and during probe the position of the Y is correct.

But when the motor is connected to the toolboard, then the position after probing is incorrect. And it just returns the target position.

dc42 · 4 Jun 2020, 13:17

Thanks for pinning it down to where the motor is connected. On my list to investigate.