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DC42--Small suggestion, if I may..

Posted by Diggrr 
DC42--Small suggestion, if I may..
May 24, 2018 01:37AM
While congratulations are in order for the new board release (it's good to see Duet not resting on laurels), had you given any thought to producing a CNC board?
Something along the lines of screw shield with NO drivers on board, but screw connections for 4 external drivers (en/step/dir/+5v for each). 0-10v for spindle control, or even modbus and all the switch and e-stop screw connections.

An RTOS system running g-code from uSD would tickle me greatly.
Ethernet connected.

Just planting a seed....winking smiley

Edited 1 time(s). Last edit at 05/24/2018 01:41AM by Diggrr.
Re: DC42--Small suggestion, if I may..
May 24, 2018 01:58AM
That's something we might consider when we have more experience with using Duets to control CNC machines. In the shorter term we may do a 0-10V output daughter board for the existing Duets to connect the VFD.

We won't be moving to screw terminals because OEMs hate them, they make wiring up the machine take much longer and greatly increase the chance of mis-wiring.

Edited 1 time(s). Last edit at 05/24/2018 02:01AM by dc42.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: DC42--Small suggestion, if I may..
May 24, 2018 02:21AM
Good points.
But buying a board with drivers is like buying shoes for the wife---money out of pocket for something I'll never use.
I'll trudge along until then.

Thanks much for your time!
Re: DC42--Small suggestion, if I may..
May 24, 2018 04:38AM
I take your point, buying a board with expensive on-board drivers is a waste if you are going to use external drivers. But are you sure you need external drivers? What size stepper motors did you have in mind?


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: DC42--Small suggestion, if I may..
May 24, 2018 12:04PM
NEMA23 5A 3Nm. I'm building a metal cutting mill soon.
Currently building a wood carving mill with 3A 1.9Nm steppers, and they should do well on my SBD109A's.
It's not all about current rating though, I'd prefer to use 48V power for more accurate stepping at higher rates.
Power requirements increase quickly when using meter long 16mm+ ball screws pushing a 6 Kilo gantry, and a driver-less board allows easy scaling of your fine Duet/Firmware to whatever monster I can dream up. smiling smiley

Edited 3 time(s). Last edit at 05/24/2018 01:17PM by Diggrr.
Re: DC42--Small suggestion, if I may..
May 24, 2018 01:19PM
Quote
Diggrr
NEMA23 5A 3Nm. I'm building a metal cutting mill soon.
Currently building a wood carving mill with 3A 1.9Nm steppers, and they should do well on my SBD109A's.
It's not all about current rating though, I'd prefer to use 48V power for more accurate stepping at higher rates.
Power requirements increase quickly when using meter long16mm+ ball screws.

Mills generally move slowly, so unless you are using fine-pitch screws for the axes to give a high steps/mm, you probably don't need more than 24V. Use the motor back EMF calculator at [configurator.reprapfirmware.org] to check.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: DC42--Small suggestion, if I may..
May 27, 2018 11:13PM
Okay, so what exactly is the calculator showing me?
I have to set travel at 4mm/s @ 24V/2.2A to make all the fields green in the box below, which would seem quite slow.

The stepper calculator here Allaboutcircuits shows I should hit a more proper 52.5mm/s.

Thank you for your time BTW smiling smiley

Edited 1 time(s). Last edit at 05/27/2018 11:37PM by Diggrr.
Re: DC42--Small suggestion, if I may..
May 28, 2018 02:06AM
Quote
Diggrr
Okay, so what exactly is the calculator showing me?
I have to set travel at 4mm/s @ 24V/2.2A to make all the fields green in the box below, which would seem quite slow.

The stepper calculator here Allaboutcircuits shows I should hit a more proper 52.5mm/s.

Thank you for your time BTW smiling smiley

What values are you entering into the calculator?


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: DC42--Small suggestion, if I may..
May 28, 2018 03:40AM
Ah, redid it and found my error converting holding torque Nm to Ncm (190 for my NEMA 23, not 1900...oops).
It now shows 42mm/s as the maximum rate to get all the categories green.

Approximate peak back EMF due to rotation per motor: 23.6 V at 42.0 mm/s
Approximate peak back EMF due to inductance per motor: 2.6 V at 42.0 mm/s
Step pulse frequency: 26.9 kHz at 42.0 mm/s
Speed at which torque starts to drop (low slip angle): 21.6 mm/s @ 13.9 kHz
Speed at which torque starts to drop (high slip angle): 29.7 mm/s @ 19.0 kHz

But still the question: is the back EMF a concern for the Duet specifically, or for an off-board driver?
All values are doubled at 48 volts also..
Curiosity more than anything.

Edited 1 time(s). Last edit at 05/28/2018 03:48AM by Diggrr.
Re: DC42--Small suggestion, if I may..
May 29, 2018 01:48AM
The back EMF is a concern for any constant current stepper driver. The calculations show the speed at which the driver becomes unable to maintain constant current.

When the speed is high enough so that there is insufficient supply voltage, microstep accuracy is also very poor, although that isn't normally a concern during high-speed moves.

Edited 1 time(s). Last edit at 05/29/2018 04:21PM by dc42.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: DC42--Small suggestion, if I may..
May 29, 2018 03:13AM
Excellent explanation, thank you!
Re: DC42--Small suggestion, if I may..
June 17, 2018 06:31AM
Quote
Diggrr
. 0-10v for spindle control....

problably you already know but my vfd has also 0-5v input and 4-20ma for controliing the spindle. but if you go with modbus that would be enough.


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Re: DC42--Small suggestion, if I may..
June 17, 2018 04:20PM
I did not know that, I haven't yet bought my spindle.
It had confused me as to why arduino boards have a 0-5, yet other boards have a 0-10..thanks!
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