@dc42 If I were you, I would forget about backwards compatibility! As things evolve, at some point a bold decision must be made and a clean sheet approach must be considered. As you mention, in the end, only changes to the config.g file, in order to properly configure things as they were in firmware versions 1 and 2, this is not a major problem.

In the end, based on my own experience with similar situations, with or without the full backwards compatibility roughly the same amount of support issues will appear on the forum.

I personally vote for this significantly improved flexibility in using the I/O capabilities of the boards. And, in the end, it might have the desirable side effect of removing some of the support issues related strictly to improperly configured or connected I/O pins (like the rather odd mapping of the homing/limit sensors). By having no default assignment and having to define everything in config.g would actually make things a lot easier to follow and some mistakes could easily be avoided. As such, I would make mandatory even the M584 command, not defining any default axis or extruders at all if it is not there!

On the issue of multiple steppers on the same axis, a solution similar to what I did for WorkBee should also be allowed. When squaring a CNC a known offset for a specific stepper on an axis might be required (try positioning a homing switch with 0.01mm accuracy!). But this can be discussed when time comes....

I have a similar looking PWM to 0-10V converter connected as follows:

• DIN- - FAN1-
• DIN+ - V_FAN
• 12-30V - the Duet power supply
• AO/A0 - the VFD VI pin (VI1 in your case)
• GND - the Duet power supply and the GND pin on the VFD (can also be named ACM)

Set the PWM input signal level to 24V or you might break the optical coupler at its input.

On the VFD you also need to short FWD (can also be named FOR) to XGND (can also be named DCM or COM).

Enable the spindle on FAN1 output by adding the following into the config.g script, replacing the R24000 parameter with the maximum speed of your spindle:

M453 P21 R24000 F1000
M563 P2 S"Spindle"

Specify in the post-processor of the CAM software:

• M3 {$s} G4 S30 for spindle start - this is for CamBam, for other CAM software the {$s) variable might look differently; adjust the S30 to allow the spindle reach maximum speed before plunging into the material.
• G4 P0 M5 for spindle stop - the default M5 doesn't wait for all movement to finish!!!

Check in the VFD manual for P00.01 and P07.08. They both need to be properly set in order for the VFD to use the signal on VI1 for speed control. In case of Huanyang VFDs, check PD001and PD070.

The VFD might also have some small switches near the control terminals connector, usually undocumented.

I also have a spindle warmup macro that I run before doing the first machining of the day, as you need to get the grease fluid enough for top speed:

M3 S5000 G4 S120
M3 S10000 G4 S120
M3 S17000 G4 S120
M3 S24000 G4 S120
M5

With the above, the spindle RPM will be correct at top speed, being 10-20% higher at lower RPMs.

@dc42 In CNC the G0 moves are usually done at a configurable height that is called "clearance height", usually 3-5mm, with the CAM software usually raising the spindle as high as instructed and then moving to the next machining coordinate. Of course, G0 is almost always used to raise the spindle and, in specific situations, it may also be used to lower it until it gets pretty close to the material, using G1 for the last fraction of mm.

Doing G0 moves too close to the material surface is generally a CAM software (usage) mistake.

@jrow Indeed, you have installed the filter in the wrong direction. The 3-pins end is for the load, as indicated on its label (though pretty uncommon!). Also, don't expect much from it as the common mode inductor and the X capacitor are pretty small. Better go for something like this one - https://www.conrad.com/p/schaffner-fn2090-16-06-emi-filter-250-v-ac-16-a-4-mh-l-x-w-x-h-1135-x-575-x-454-mm-1-pcs-554095. While it is significantly expensive, from my own experience it makes a huge difference.

But this filter just prevents electrical noise from getting back into the supply lines. You also need to insure that the VFD is properly grounded and also check that the spindle is really grounded. I had to make myself the ground connection into my spindle as the Chinese ones usually are not properly grounded.

On my CNC I have a Huanyang 1.5kW VFD inverter and a 24V power supply from Meanwell for the Duet. Never had any EMI problems and I have no line filter on the inverter. For connecting the spindle to the VFD I use a 4-core Lapp cable. The 4 cores are slightly twisted for maximum flexibility and that also helps a little bit on the electrical noise side.

@dc42 When talking to Chrishamm, could there be an extra set of jog buttons for 0.01mm steps? When properly aligning the gantry with the machined piece, sometimes it is very important. Right now I have to manually send G0 commands for that! All other CNC software include support for that.

After trying to machine some small Aluminum parts, I had problems even at 1200mm/min. In the end, after doing a lot of tests and studying the problem, the CAM processor is the main culprit. I use a lot of trochoidal milling as it produces much better results on a not-so-rigid machine. The CAM software produces some sudden direction changes in specific situations, so specific that many times they do not happen at all.

I have found a pattern that easily reproduces the problem. In the end it was the maximum jerk being too high! 900mm/min instantaneous speed change for an 10kg gantry is anything but normal. Maximum feedrate of the WorkBee is 2500mm/min!

As a side note to this issue, and any other issue that might be related!

I had a project in which we used huge amounts of connectors pretty much identical to the ones used on the Duet boards. It was not the first project, as I had very good previous experience with the same type of connectors. Some if the guys crimping the pins on the wires misplaced them in the crimping tool and they have squeezed the contact area way to much. We had to get the pins out of the plastic bodies and re-spring them for quite a few of the cables. The problems were random, so finding the actual cause was anything but simple!

Also, we saw that even "compatible", these connectors are not 100% identical between manufacturers, with slight variations in the latching dents and the actual pin shape. If all sourced from the same manufacturer, everything is OK. But this is a relatively low cost connector, though a pretty well designed one, so there are a lot of manufacturers and only few suppliers guarantee the manufacturer (go for big suppliers like Farnell, Mouser, DigiKey, TME in order to have guaranteed supplier, but avoid generic ones - like Multicomp for Farnell). I think on Duet the connectors are from Wurth!

With the release of the 1.21 firmware all the missing functionality for CNC, at least what I consider mandatory, is available, so I could finally ditch the good old GRBL. The machine is a 750*750mm WorkBee, screw driven, with 3.0A steppers, home switches and limits on all axis. There are several notable differences from the standard WorkBee that influence the configuration scripts:

• home switch on the slave Y axis to allow aligning the gantry, not available by default;
• limit switches are not available so far in the default configuration, so a lot more wiring is needed;
• the Z axis is longer to allow deeper reach for a special setup.

The controller is a Duet3D Ethernet, rev 1.02, updated to firmware 1.21.

For now the steppers have been limited to 2A. Tomorrow I intend to make fan mounts to insure that the drivers are properly cooled. That should allow going up to 2.4A as per the Duet3D documentation, or even more if the limit is removed at a later time.

The connections are pretty straightforward - X, left-Y and Z connected to the corresponding axis and right-Y connected to E0. Home and limit switches are NC, connected in series for each axis, the series connection being done close to the controller. All cables are shielded, with the shield connected to ground on the controller side and left floating at the stepper/switch.

There is also a tool height probe, also based on a NC switch, connected to the PROBE connector.

With the above said, this is the config.g file (produced by RRF configuration tool and then edited):

[[language]]
; General preferences
M111 S0                     ; Debugging off
M453                        ; CNC mode
G21                         ; Work in millimetres
G90                         ; Send absolute coordinates...
M83                         ; ...but relative extruder moves
M555 P2                     ; Set firmware compatibility to look like Marlin
; Automatic saving after power loss is not enabled

; Endstops
M558 P5 H5 F100 T2500      ; Set Z probe type to switch and the dive height + speeds
G31 P600 X0 Y0 Z39.55      ; Set Z probe trigger value, offset and trigger height
M557 X15:530 Y15:500 S20   ; Define mesh grid

; Drives & Axis
;
; Define axis X on drive 0, axis Y on drives 1 and 3, axis Z on drive 2 and dummy axis U on drive 9
; Show only axis X, Y and Z
M584 X0 Y1:3 Z2 U9 E4:5:6 P3
;
; Set stepper drives parameters for all the used ones
M569 P0 S1                       ; Drive 0 goes forwards
M569 P1 S0                       ; Drive 1 goes backwards
M569 P2 S1                       ; Drive 2 goes forwards
M569 P3 S0                       ; Drive 3 goes backwards
M350 X16 Y16 Z16 U16             ; Configure microstepping with interpolation
M906 X2000 Y2000 Z2000 U2000 I30 ; Set motor currents (mA) and motor idle factor in per cent
M84 S30                          ; Set idle timeout
;
; Set axis dynamic parameters
M92 X400 Y400 Z400 U400          ; Set steps per mm
M566 X400 Y400 Z12 U400          ; Set maximum instantaneous speed changes (mm/min)
M203 X2500 Y2500 Z2500 U2500     ; Set maximum speeds (mm/min)
M201 X150 Y150 Z150 U150         ; Set accelerations (mm/s^2)
;
; Set axis travel distances
M208 X0 Y0 Z0 U0 S1              ; Set axis minima
M208 X545 Y515 Z200 U515 S0      ; Set axis maxima
;
; Set axis endstops
M574 X1 Y1 Z2 U1 S1              ; Set active high endstops
M581 X Y Z U S1 T0 C0            ; Enable endstop triggers while machining

; Heaters
M140 H-1                   ; Disable heated bed

; Tools

; Network
M550 PWorkBee              ; Set machine name
M540 PBE:EF:DE:AD:FE:ED    ; Set MAC address
M552 P192.168.1.200 S1     ; Enable network and set IP address
M553 P255.255.255.0        ; Set netmask
M554 P192.168.1.254        ; Set gateway
M586 P0 S1                 ; Enable HTTP
M586 P1 S0                 ; Disable FTP
M586 P2 S0                 ; Disable Telnet

; Fans
M106 P0 S0.3 I0 F500 H-1   ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
M106 P1 S1 I0 F500 H T45   ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
M106 P2 S1 I0 F500 H T45   ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned on

; Custom settings are not configured

; Miscellaneous
M501                       ; Load saved parameters from non-volatile memory

; Change to workplace coordinates set 1
G54

homez.g

[[language]]
M581 Z S-1 T0 C0  ; disable trigger for endstop Z
G91               ; relative mode
G1 S1 Z300 F1000  ; move Z towards the switch until it triggers
G0 Z-5            ; move Z back 5mm
G1 S1 Z10 F100    ; move Z slowly towards the switch until it triggers
G0 Z-1            ; move Z back 1mm
G90               ; back to absolute mode
G92 Z200          ; reset the Z coordinate
M581 Z S1 T0 C0   ; enable trigger for endstop Z

homex.g

[[language]]
M581 X S-1 T0 C0   ; disable trigger for endstop X
G91                ; relative positioning
G1 S1 X-1500 F1000 ; move quickly to X axis endstop and stop there (first pass)
G0 X5              ; go back a few mm
G1 S1 X-100 F100   ; move slowly to X axis endstop once more (second pass)
G0 X1              ; go back a few mm
G90                ; absolute positioning
G92 X0             ; reset the X coordinate
M581 X S1 T0 C0    ; enable trigger for endstop X

homey.g - The special line with "G0 Y0.09" is needed in my setup to fully align the gantry. No matter how much I try, there is no way to precisely place the homing switch on the slave Y axis and there might be other small mechanical differences. The offset could be applied either to Y or U axis, depending on the actual situation - the X axis must be parallel to the front beam of the machine frame and the offset can only be positive.

[[language]]
M581 Y U S-1 T0 C0        ; disable trigger for endstops Y and U
M584 Y1 U3 P4             ; separate Y and U axis for aligning them independently
G91                       ; relative positioning
G1 S1 Y-1500 U-1500 F1000 ; move quickly to Y and U axis endstops and stop there (first pass)
G0 Y5 U5                  ; go back a few mm
G1 S1 Y-10 U-10 F100      ; move slowly to Y axis endstop once more (second pass)
G0 Y0.09                  ; fully align gantry
M584 Y1:3 U9 P3           ; combine again the master and slave Y axis
G0 Y1                     ; go back a few mm
G90                       ; absolute positioning
G92 Y0                    ; reset the Y coordinate
M581 Y U S1 T0 C0         ; enable trigger for endstops Y and U

homeall.g - Partially rely on the other homing scripts in order to reduce the number of files to edit if some parameters change.

[[language]]
; first home the Z axis
M98 Phomez.g
;
M581 X Y U S-1 T0 C0          ; disable trigger for endstops X, Y and U
M584 Y1 U3 P4                 ; separate Y and U axis for aligning them independently
G91                           ; relative positioning
G1 S1 X-550 Y-520 U-520 F1000 ; move quickly to X, Y and U axis endstops and stop there (first pass)
G0 X5 Y5 U5                   ; go back a few mm
G1 S1 X-550 Y-520 U-520 F100  ; move slowly to X, Y and U axis endstops once more (second pass)
M584 Y1:3 U9 P3               ; combine again the master and slave Y axis
G0 X1 Y1                      ; go back a few mm
G90                           ; absolute positioning
G92 X0                        ; reset the X coordinate
M581 X Y U S1 T0 C0           ; enable trigger for endstops X, Y and U
;
; redo Y axis homing for fully aligning the gantry
M98 Phomey.g

@shen
I would avoid even to suggest such a behavior unless it is made optional. The image actually depicts a corner replaced by an arc. This is a decision to be made when generating the GCode for a job (3D printing or milling) and not to be done by the controller in the machine. Just imagine items with sharp edges that must mate properly. With the suggested path that might no longer happen.

If the path smoothing is desired because of the STL 3D models, why not look for a slicer that supports arc fitting and generates G2/G3 commands? Why not looking for a GCode processor that reads the file produced by the slicer and changes it to G2/G3 commands where possible? In the end the controller should do exactly what it is instructed to do.

As a side note, it might be more interesting to do a side-by-side comparison between Duet and some board that supports a firmware with higher order motion planning. Is there any difference? Is it really worth the effort?

@dc42 That is great news! This single problem prevented me from using the fastest possible feedrate and I also had to reduce the jerk in order to avoid it in most cases.

When the new firmware is released, I will do some air cutting and see how it goes!

I was among the first users of Duet on a CNC machine over four years ago. Back than I had a genuine, first version, Workbee, with several years of using GRBL on another low cost CNC. While Duet was lacking features of GRBL that I was already used with, the old Pololu DRV8825 drivers were not up to the task and I decided not to spend to much on proper Leadshine drivers. So Duet looked perfect as a hardware platform.

With CamBam for the CAM part, configuring it to generate a GCode that was understood by Duet back then was OK (G2 and G3 were not even planned back then, not to mention the work coordinates!). I wrote on the forum about the issues that I have found, I complained about some of the missing features, and things slowly got better.

These days the Duet boards are a good choice, depending on the CNC you want to control.

3 years later problems started to creep in. Being an Electronics engineer, I started digging. It all came down to the on-board drivers. Randomly, only at powering on, they reported disconnected and/or shorted steppers. I checked all connections, I replaced connectors, I ended up replacing cables - no luck! And, worse, sometimes I was not able to use the CNC for a whole day. Once started, all went flawlessly! I was not the only one with the symptom, just search the forum for "phase disconnected". There was no clear solution to the problem!

My ten cents - even if properly cooled, using the on-board drivers at 2.4A (my steppers are rated for 3A) for hours at a time is affecting them over time. The higher power drivers on the Duet 3 board should be better. But there is another problem - the supply voltage! You can't get proper performance from the steppers on a larger CNC without using at least 36V as supply. Even the new Duet 3 boards are limited to 32V.

So I decided to put the Duet board to storage and moved to PlanetCNC MK3 with Leadshine drivers. The bill was slightly higher, but not hugely higher (less than double!). And it comes with a lot of CNC specific bells and whistles.

@joaquin_suave You can get this one - https://ro.mouser.com/ProductDetail/Cosel/PJMA1000F-36?qs=DRkmTr78QARflml570Qxjw%3D%3D - while announced for 36V, it can be adjusted from 30.8V to 40.8V. Unfortunately 32V is not that usual and 20A is anything but low current...

@zapta Quite interesting. Those might be suitable for axis 4 and 5 in a prosumer CNC...

@zapta said in Why not brushless motors in direct drive extruders?:

This is probably a matter of demand. With sufficient demand, this can be a much lower cost IC. The question is, is it useful for large scale applications?

Demand builds up when there is a real need for such a solution. I see a need for it in completely different applications, but not in a 3D printer, not even in a prosumer one. In a professional one, maybe!

Has anyone complained about the steppers limiting the performance or the quality of the 3D printers on this forum? I have not personally checked, but from already 4 years of browsing I don't recall anything significant. Of course, I'm not discussing about faulty steppers or super cheap steppers assembled in a barn in China (by the pigs grown up for feeding the family over the next year) or poorly chosen (wrong size for the job) ones. There are very good quality steppers at very decent prices, most of them manufactured in China. And they are not even difficult to find.

So with a relatively low demand, combined with the high current involved in those drivers (120A peak current! those transistors are anything but cheap!) I don't see the solution getting significantly cheaper. Overall you must also factor in the high current power supply. 24V at 60A is almost 1.5kW peak power for one of these motors. While the average required power is significantly lower, the PSU should be ready to handle those peak currents. Look at this just for reference - https://www.onlinecomponents.com/en/mean-well-usa/rsp200024-43879729.html.

As for recognized professional solutions, check this servo with integrated driver - https://www.sorotec.de/shop/JMC-Servo-Motor-with-integrated-driver-100-Watt---36-Volt---3000-1-min.html. Significant torque with very high speed as 36V and 6A peak current.

@zapta said in Why not brushless motors in direct drive extruders?:

I am not an expert but isn't this what gears do, trading between torque and speed?

Of course, but those gears and their supporting plates start adding to the weight. And the whole discussion started from the 30g BLDC motor.

@rjenkinsgb said in Why not brushless motors in direct drive extruders?:

They both use permanent magnet rotors and wound stators.
(Steppers do not have plain iron cores - if you turn one, you can feel the rotor magnet jumping from alignment with one stator pole to the next).

Unless they are variable reluctance ones!

@zapta Extruding is all about torque at relative low RPM. This is what I see for those really interesting solutions:

• Maximum torque 1.99Nm or 3.86Nm, but that comes with a peak current of no less than 65A!!!
• A big note - "*Note that torque and current ratings are with Extremely good forced air cooling"
• RPM at no load - 5760RPM or 8640RPM.

The torque I get, at much lower speeds of course, from a rather standard NEMA 23 at 2.4A and no need for extra cooling.

And the pricing... the driver is a merely 179EUR. You get 3 or even 4 decent Leadshine drivers for that amount!

Again, that is exactly what I have stated... it is a solution, bot not for extruding the filament! I would see it more likely for the gantry movement where, in a 3D printer, the required torque is very low but the speed is high. But, still, it might not justify the extra costs...

@pertti A stepper motor is the most simple model of brushless motor. The ones that you think of, as used in RC models, have 3 phases (they have 3 coils) and are designed for a very high power/weight ratio and quite high RPMs. Also they produce a lot of heat that must be somehow removed - not a real problem in any fast moving model/drone.

The steppers are simpler as they use just two phases (they have just two coils), are designed for much lower RPM and much higher torque and are cheaper as they need just iron (high quality magnets are crazy expensive since the whole EV craziness - but this off topic!). Not to mention the significant precision. Also, the overall required power is significantly lower and also is the produced heat.

While you don't see why filament extrusion requires precision, just think about a very finely detailed object that needs printing. That implies a lot of quite dramatic direction changes, so the extruder precision is important in order not to over- or under-extrude. If you follow the various topics on this forum, you will see a serious debate on various extruding rate estimation/models. If you consider the 1.75mm filament and a 0.3mm nozzle, for every 1mm of printer head movement you need to extrude just under 0.03mm of filament.

What you are suggesting is to take a motor that literally has only much fewer steps - twice the number of magnets on the rotor, design a microstepping controller for it and use it instead of the well proven steppers. The ESC in any RC model is, in the end, just an oscillator with 3 outputs with 120° between their phases and a frequency matched to the required RPM. It doesn't have all the blows and whistles in any cheap stepper driver!

So, while not impossible, it sounds more like reinventing the wheel. And based on my own experience I bet that the final result, for the same performance, will be more complex, heavier and a lot more expensive!

P.S. Please don't get me wrong! I'm not against new solutions. Even at work I'm known for looking first of all for cons in any technical suggestion and I have my own share of "exploring the uncharted territories" activities. It's just that I'm used to look at all aspects of any alternative technical suggestion. Some of them I gladly embrace myself and help testing/developing!

@deckingman From the picture, the printer we are discussing about has moving steppers. So the heat dissipation would happen only if the metallic plates would be quite massive. A simple solution would be to have the Y axes steppers fixed in the rear or the profiles and the belt looped over a pulley or a large idle wheel in the front. That simplifies cabling, hugely improves steppers cooling and reduces the gantry weight.

As for static electricity breaking the steppers, never! While static electricity may cause you small shocks, due to the relatively high voltage, the current is almost impossible to measure due to its very low value and too short time. The stepper coils are designed to handle relatively high currents when compared to the current in a static discharge.

But the high voltage in a static discharge is a guarantee for "success" when we consider the stepper driver. While it may not break the driver, it may briefly (or permanently, but then you blame the driver for breaking the stepper!) open all the semiconductor junctions in it, practically getting a large current into the stepper, with no current limiting logic. That may break the stepper! But I never saw that happening!

Static electricity buildup requires a multitude of conditions to be met simultaneously. I don't see how those could be met in a 3D printer supplied, usually, with 24V, unless we are discussing of a large amount of hot air moving inside the printer so that it would get really dry. Normal air humidity reduces the chance of static electricity buildup.

And even with Aluminum plates, there is no proper electric connection between the elements, at least not while using the V-slot wheels. Even with other solutions of linear bearings there is no guarantee as the V-slot profiles are usually anodized, so they have a non-conductive protective layer.

@michaelr123 If you rotate the profile by 90° you will start having issues on the Z axis. If you want something really right, just replace the profile with a beefier one. With minimal changes, the 4040 should be significantly less susceptible to bending. Or, even simpler, attach another 4020 or 20*20 profile to your existing one. As you have nothing running on the lateral slots, just drill 5.5mm holes in through the center of the extra profile, larger through the V-slot so that the screw head will pass through, and secure the extra profile with slot nuts to the existing profile.

For a 1m profile use 5 or 6 screws evenly distributed over its length. Minimal effort for a significant rigidity gain.

You could stick to 3D printed brackets for now, but go for something like PETG and make them a lot thicker. It also helps to design them with guides fort the rails to slide in, so you get the required 90° in the corners a lot easier.

For the stepper metal plates, you should be able to find shops that provide laser cut Aluminium or steel plates. 6-8mm aluminum or 4-6mm stainless should do the job a lot better than the plastic ones. Thicker plates are needed only for milling CNCs. Those companies usually need just a DXF or a technical drawing of the plate.