Duet for Lowrider CNC

doigal

Hi all,

At some point next year I hope to be building a lowrider style CNC machine. (See https://www.v1engineering.com/the-lowrider2-cnc/ ) I'm currently hunting around for parts, and just want to check a couple of things before ordering a Duet to run it all.

Spindle control. I plan to use one of the Chinese VFD controllers, which requires either 0-10v or MODBUS input. I know the 0-10v can be achieved via an external module (this was discussed on another thread) but is there any way to do modbus?
Endstops. I plan to use dual endstops on the Y and Z axis, by running them on separate drivers and virtual axis (U and W) and constraining the machine to three visible axes. I think this has been discussed before, and I'm reasonably sure I have the config code in my head for this. My question is - can duet also support a max endstop to serve as a limit switch? I know that I could set soft endstops, but they only work if the machine is homed every time. Whilst that will probably be the norm I don't want to be forced to do it.
Z end stops. Kinda further to the second question. I want to home to Z max on both Z axes, and then I need to have a touch probe (Contact on the tool to a touch plate of known height) - effectively a zmin probe for tool height but after a z max homing for squareness. Is this possible using the z probe connection? I believe this is refered to as mode 5, I want to make sure that this and the Z max is possible.

Thanks, sorry if any of these are silly questions!

T3P3Tony

@doigal looks fun.

No to modbus at this point I would need to look at it in more detail to see how much work it was to add.
As you say the dual axis is described in other threads. While you can't set up seperate max and minutes endstops you could wire in a single trigger to switches at the top of each axis to pause the machine if it was triggered.
That is fine.

@Danal and @Catalin_RO may have more detailes input from their experience

Jacotheron

Having a Duet controlled CNC machine myself, a few details (my machine have a workable envelope of 1325x1285x150mm - so it is quite big).

My spindle is simply a Makita, so only manual speed control here.
Endstops. On my machine, I only have Min endstops, and due to most projects starting close to Home, I home before every job. Further I make use of the Coordinate Offsets (https://duet3d.dozuki.com/Wiki/Gcode#Section_G54_to_G59_3_Select_coordinate_system). Basically this allows us to define a Virtual Origin, with all moves being executed relative to this origin, while the Duet knows to keep inside of the machine bounds (or terminate when going outside). I also store my machine with the spindle close to or at Home, so Homing is quick.
Z height probe. I have a probe like you describe (mine have a circular touch plate and a crocodile clip to attach to the tool, functioning as a NO switch). While mine is connected on the Z endstop, it is best to have it on the Probe connection (easier to configure). I also have my Z max set as the motor load detection (so I Home Z to Max, then perform the probe on my material for the Z0).

dc42

@doigal, from my research into ModBus I see that it normally uses either Ethernet or async serial at the hardware level. Which one do those VFD controllers provide?

doigal

Thanks for all the replies!

@dc42 said in Duet for Lowrider CNC:

@doigal, from my research into ModBus I see that it normally uses either Ethernet or async serial at the hardware level. Which one do those VFD controllers provide?

Im honestly not that sure and cant claim to know much about the protocol. My plan was to use a Huanyang style VFD from alibay, and they seem to be able to be controlled via either analog or modbus. I know I'll end up with long wire runs from the duet to the VFD, so was hoping to use digital rather than analog.

T3P3Tony

@doigal can you try and dig up or request a datasheet of some description?

doigal

@t3p3tony The manual (a manual at least) talks about it towards the end:
http://www.cnczone.ru/forums/index.php?act=attach&type=post&id=4180

Theres some other links about it here as well.
http://fightpc.blogspot.com/2014/10/vfd-control-with-arduino-using-rs485.html
https://www.cnczone.com/forums/phase-converters/91847-software.html

I dont have one in my hands to play with, im still working out how much the lowrider CNC would need to be modified to fit the spindle in.

dc42

The VFD manual says that MODBUS is implemented over RS485. So one option would be for you to connect an RS485 transceiver to the PanelDue port, wire that to the VFD, and modify RepRapFirmware to send the required MODBUS commands to that port.

The VFD manual also says that it supports 4-20mA current loop for frequency control. So another way would be to convert one of the PWM heater or fan outputs to current loop. We have a design for doing that.

doigal

@dc42 said in Duet for Lowrider CNC:

The VFD manual says that MODBUS is implemented over RS485. So one option would be for you to connect an RS485 transceiver to the PanelDue port, wire that to the VFD, and modify RepRapFirmware to send the required MODBUS commands to that port.

So basically what you are saying is that its possible? perfect!

I know that it can be done as a 0-10v input (the 'analog' method), i think thats been discussed here before.

dc42

@doigal said in Duet for Lowrider CNC:

So basically what you are saying is that its possible? perfect!

Possible if you are happy to modify the firmware. The current loop option or a 0-10V option would not require any firmware modifications.

doigal

Just a quick update, I ordered one from the local swedish reseller, and 10 minutes after getting it out I had it working on a test bed for dual endstops, exactly as expected! I'm not sure anything has been so simple before!

This is just a simple spinner, which plugs into Y and E0. E0 is defined as axis U, and the config file has M584 Y1:3 U3 to join them at the hip. The homing file seperates them again, and homes them both individually. Its purely for me to learn how it works in practice.

So far it works perfectly!