I'd like to revive this subject as can you share some experience?
We are building a large coreXY with 4 XY motors (nema 17 60mm)
I wonder if there are any reasons not to connect two motors to one driver?
The drivers are 4.5A so there is some overhead and the setup will be 48 V. We used nema 23 with one driver on Duet 2 ethernet but only on Z axis so they have much less to do and worked for years without problems, but this time they are on XY and there will be a lot of long fast travels.
@dc42 Thanks a lot David, I should definitely forget it 
Is it possible to resolder a MOSFET and a few small warehouses on the board to be able to apply 48 V or should I forget it ?
We have a fair amount of older MB6HC on large machines and 48 V would greatly help with long fast travels.
I'm aware we can order new Duets or expansion boards.
@sebkritikel Thanks, I'm concerned only about the motor characteristics of servos / steppers.
With fast long travels steppers have very little torque and are troublesome.
But on the other hand step dir is not a perfect solution to drive servos also.
There is little info about these subjects so probably we will go all Duet to save time and trouble.
We had leadshine easy servo and DCS303 connected to Duet ethernet a few years ago.
Everything was fine only the prints were wavy distorted by layer shifting or something else and after some trial and error we dropped the project.
Now a new light shines, there are better Duet expansion possibilities and more motor options.
We need very fast travels on a large machines and total immunity to position loss.
There would be two ways, and I'm not certain if the second would work at all:
What are real life differences in two ways?
Do we lose on the servo side due to 5ms min signal length comparing to probably faster stepping rate with 23 CL?
@chrishamm There is and I successfully do it by passing an iterator as "data" to POST request, it feeds the request with chunks of data. Everything is fine but it is a blocking IO. I'm trying to make it async, ond one of the ways is to pass chunks sequentially in subsequent POST requests, only RRF treats each chunk as a separate file.
I have to dig into it more and perhaps make an async iterator and use it with async uploader, which I failed to do as of yet.
This is a working non async upload code:
import requests
class upload_in_chunks(object):
def __init__(self, filename, chunksize=1 << 13):
self.filename = filename
self.chunksize = chunksize
self.totalsize = os.path.getsize(filename)
self.readsofar = 0
def __iter__(self):
with open(self.filename, 'rb') as file:
while True:
data = file.read(self.chunksize)
if not data:
sys.stderr.write("\n")
break
self.readsofar += len(data)
percent = self.readsofar * 1e2 / self.totalsize
sys.stderr.write("\r{percent:3.0f}%".format(percent=percent))
yield data
def __len__(self):
return self.totalsize
def sendme():
requests.get(baseurl+'/rr_connect?password=reprap')
requests.post(url, data=upload_in_chunks(afile, chunksize=10))
I try to write a simple python software to upload gcode to a machine in async manner.
I have it working synchronously by passing an iterator to request object, but I need async to send lots of files to different machines.
A file is divided into chunks and each chunk is an async task.
The problem is that subsequent chunks gets uploaded in separate POST requests as separate files, overwriting each other, so the uploaded file has last chunks size.
I've set the X-File-Id header but it does not seem to work.
So the question is is it at all possible to send one file in many POST requests to RRF?
I cannot reliably upload a g-code file via DWC on a Linux Mint 21 machine. It starts and after proceeding for a while the connection goes down and upload fails. The printers have Duet 6HC boards with 3.4 firmware. Uploading from W10K works normally, only on Mint it fails, I tried Firefox and Brave, same result, no matter what connection settings are in the DWC. Perhaps there are some networking settings I don't know about. Did you have any problems alike?
@deckingman
Ofcourse! Thanks a lot it's so elegant!
@oozebot So it is a loop. What a nice idea.
When 2 motors are connected this way is it possible to drive only one of them (to load filament)
One way would be to create a dummy tool :
M563 P1 D1
and driving it :
T1
G1 E1500 F1000
but it is too much of a hack.
I know there is M302 P0 to allow cold extrusion, but is there a
way to force a certain piece of silicon on the board to feed pulses to connected motor?
Great, happy to hear it!
What do you mean by "loop"? Is it a physical loop of filament? Where is it placed in the printer?
I've just connected the secondary extruder (42mm NEMA 17), set it to 300 mA, and mixed so it extrudes more than tha main extruder.
We'll see how far it goes 
@dc42 Thanks a lot! works like a charm!
Have you tried a weak motor as a secondary extruder, one that would miss steps on major resistance?
I have done no serious tests yet, we use 5kg spools and have similar problem. First idea was to use two motors connected to one stepper driver, not to occupy other drivers.
Main extruder use a 200 steps 25mm motor with belt transmission 2:1 and the secondary extruder at the spool is a 400 steps 42mm (I just had it handy) to match gear ratio. Unfortunately the main one is much weaker in this setup. Perhaps it would work with two same sized motors one 200 the other 400 steps.
Missing steps is plainly a dirty hack, but in our case providing enough support for the main extruder requires only a gentle push.
Mixing would definitely be a cleaner solution but is it at all possible to use two extruders inline without fighting each other at some point?
Hi,
I'm going to add a secondary filament drive motor for at filament spool to offload main extruder. Extruder motor is 25mm 1.0A 200 steps one and the helper motor is 42mm 1.6A 400 steps one to provide the same gear ratio.
Is there a possibility to connect one motor to E0 driver, the second motor to E1 driver and drive both at the same time while extruding?
It's easy to do for Z axis with M584 X0 Y1 Z2:3 E4 or something, but M584 X0 Y1 Z2 E3:4 assigns different drivers to E0 and E1.
I'm currently on RRF 1.21 and Duet 2 Ethernet.
Connecting two motors to one driver ine series leaves the small one underpowered (it has 2x larger resistance)
Hello,
Is there any remote possibility of swapping extruder motor without turning off the printer.
If the steppers are released and there would be a switch on motor cable cutting it off, would it be safe to disconnect it and reconnect?
I was doing it illegaly with Nema 8 a couple of times and nothing bad has happened, but could it be made a safe, repeatable operation?
Peter
We use NEMA 24 motors for Y and Z axes with current set to 1.5 A and overheating pins are very common. Connectors are hot and often burn to dark brown colour around pins.
Yesterday one of the printers started to behave strangely and the problem appeared to be completely burned and detached wire, just before the crimp.
The crimps has to be high quality and strongly pushed to the pin, but to be honest many of the burnt ones I would never suspect are bad.
Just a moment ago Y axis missed some steps at the end of 30 some hour print
I think I'll just solder the motor directly to the pins instead of using connectors.
We are all on Duet ethernets, haven't tested Duet 3.
Anybody close to 4A currents on the motors with Duet 3?
The printed object is 4-6 mm smaller in X direction, Y was not measured because it's hard to measure properly and Z is just fine.
Bottom layers of the print are ok. and the top is too narrow, it looks like the print is tapered linearly from bottom to the top. There are no jumps, no missed steps, no other visible artifacts or deformation.