Suggestions on Spindle control options? (Analog, Step/Dir, ModBus)

I think you should use Modbus for controlling the spindle. There is a Modbus hal component you can use.

There is no need for super-precise control of the speed, at least normally. Rigid tapping and other synchronized moves don't require a super-precise spindle but they do require encoder output from the spindle and that you have it seems. It is the axis movement, not the spindle movement, that needs to be precise and that is normally the case.

Given that you almost have it working already with Modbus and that there are some issues with step/dir, and that it doesn't matter that much how the spindle is controlled, I would say go for Modbus.

Hakan wrote:

I think you should use Modbus for controlling the spindle. There is a Modbus hal component you can use.

There is no need for super-precise control of the speed, at least normally. Rigid tapping and other synchronized moves don't require a super-precise spindle but they do require encoder output from the spindle and that you have it seems. It is the axis movement, not the spindle movement, that needs to be precise and that is normally the case.

Given that you almost have it working already with Modbus and that there are some issues with step/dir, and that it doesn't matter that much how the spindle is controlled, I would say go for Modbus.

So yes I do have what seems is a very accurate encoder.. So when sync moves are happening its not the spindle that is having its speed modulated its the axis of movement that is having its movement adjusted... If that is the case, then yah, Modbus may be more reliable and take less fiddling given I am having to jump through some hoops to create soft start and soft start logic in the HAL.

One disadvantage of modbus is that the reversal time for rigid tapping is indeterminate
so maybe not a good choice if you are doing blind tapping

oh you mean you can't project a stop point/reverse because its not part of the servo thread which could crash the tap into the bottom of the hole PCW?

I just mean that if the command to reverse comes from Modbus,
there is no timing guarantee on the PC sending this command
since its not done in real time.

Here is an example config created by Talla83 (in German) but if you understand HAL, you should be able to adopt it to your system.

This includes M19 (Spindle orient) PID controlled, normal spindle operation via step/dir including ramp up/ramp down.

talla83.homepage.t-online.de/linuxcnc/20181124_Spindel_5i25.zip

As suggested, try not to use ModBus to control the spindle.