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linuxcnc-ethercat / linuxcnc-ethercat

LinuxCNC EtherCAT HAL driver
GNU General Public License v2.0
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ADD Velocity Mode for EL70x1 series stepper drivers #435

Open GuiHue opened 2 weeks ago

GuiHue commented 2 weeks ago

If I understood both the existing driver and the manual correctly, then:

Would it be possible to create a velocity mode for the Drivers? Applications are stuff like stepper driven pumps for MQL etc where velocity is used instead of positions.

Alternatively: Are there other ways to create pos commands from velocity inputs?

scottlaird commented 2 weeks ago

It's probably not that hard, but IIRC my EL70x1 drives don't support velocity mode. Various members of the family add and remove various features.

It'd probably be worth merging the existing 2 (or was it 3) drivers and getting feature support synced up right.

scottlaird commented 2 weeks ago

Mind you, you could probably also have something write a constant delta into the position pin every cycle. It's not ideal in a lot of ways, but it'd work in a pinch.

GuiHue commented 2 weeks ago

Scott, thanks as always. I was thinking about this today. I find the manual to be surprisingly difficult to read. Lots of stuff covered but I was unable to find what I was looking for.

By the driver lcec.0.EL7031.srv-pos-cmd is tied to 7010h:11 which according to the manual is UINT32. The pin is declared as s32 within the driver (and float in linuxcnc).

This raises two questions: 1) What does srv-pos-cmd expect? An absolute position? Or an incremental position to be driven within the next cycle? 2) How is direction towards the Driver handled? If 7010:11 is UINT32, it doesnt have direction, right? In the write function of the driver I could not identify a bit that handles direction.

If 1) is absolute, than handling an extended period of constant velocity may lead to an overflow of the variable in which case I do not know what the driver will do. Admittedly UINT32 is large and the pump is really slow.

scottlaird commented 2 weeks ago

So, er, we kind of do support velocity mode for these, in an annoyingly weird way.

The EL70x1 driver is position-only, while the EL7041 drive is velocity-only.

Odds are you could do a quick hack and remove your device's PID from the 70x1 driver and add it to the 7041 driver and it'd mostly just work.

These should really just be a single driver, with selectable position/velocity settings, except that might be fun if we need to default to position or velocity mode depending on which driver originally supported the device, just for config compatibility reasons. I haven't read through the two drivers enough to see what that'd take today, but I doubt it's that much work.