replacement motor(s) / i3-MK2 ?  

Re: replacement motor(s) / i3-MK2 ?

Just a quick comment: Always talk to the Prusa folks about the spare parts (Live Chat in the lower right corner of the shop). Just because they're not listed or listed as sold out in the shop does not mean Prusa cannot send you spare ones in an emergency. You just gotta ask.

Re: replacement motor(s) / i3-MK2 ?

Jeff

The low value "shunt" resistor is there to measure voltage drop and thereby the stepper drivers can calculate the current draw which is then limited to the value set in firmware.

So if you get replacement steppers with similar values to those you measured, they will be fed with the same voltage and current as the originals and thereby produce similar output values.

The current setup only powers the motors at about 0.5Amp (I am now working from memory, and that figure may be very wrong...) and less when in quiet mode. The half amp is about one third of the available current.

The motor power can be set using GCode command M907.

Peter

Re: replacement motor(s) / i3-MK2 ?

thanks for your ansers !
@stephan.k:
in case of emergency, i wouldn't hesitate to use the chat channel to the prusa sales team. but actually i'm glad that there is no case of emergency 😉 .
just want to be prepared...

@PJR:
yeah, the shunts are there to limit the phase current's. no doubt about it. the software is able to control all the different reference voltages for the five A4982 drivers thru programming the AD5206 chip (6-Channel, 256-Position Digital Potentiometer) and therefore able to set the max. current (I=Vref/(8 x Rshunt)). :geek:

so when the phase current is limited to a maximum of approximately 0.5A, i won't notice a difference when using the 12V NEMA-17 steppers, that's good to know.
😀

Re: replacement motor(s) / i3-MK2 ?

oops, still have to ask: does the i3-MK2 use 1.8° steppers, or 0.9° ???
first i assumed 1.8° (as the most 3D printers), but now i found a motor that matches very good to my measured resistance and inductance values, which has 0.9°...
❓ ❓ ❓

counting the number of revolutions of y- and x-stepper and measuring the bed movement, i have to assume that the y- and x- motors are 0.9° ones, otherwise the achievable resolution would only be 0.16mm. with 0.9° steppers one could achieve an x/y resolution of 0.08mm.

Re: replacement motor(s) / i3-MK2 ?

The originals use 1.8 degree steppers. But I have been tempted to install 0.9degree motors for greater precision (especially the extruder).

Being pedantic "limit the phase current" no, they are there as voltage sensors - to measure the drop from which the current can be calculated. Sorry...

Peter

Re: replacement motor(s) / i3-MK2 ?

The originals use 1.8 degree steppers. But I have been tempted to install 0.9degree motors for greater precision (especially the extruder).

hi peter,
how can you tell the firmware that you're using 0.9° stepper(s) instead of 1.8° ones, or vice versa ?
or do you virtually resize your bed and models by +100% for the axis with the 0.9° motors ?

regarding the idea to do this with the extruder motor: do you think this really makes sense ? the extruder motor drives the filament by friction with a milled pulleye. i don't think that it'll really improve anything in its precision to feed the hotend with filament.

hmmm... are you sure that all the genuine motors are 1.8° ones ?
when i take my measurements and calculations in account, the Z and the extruder steppers are 1.8° ones and the x- and y-steppers are 0.9° ones.
anyone here who knows this for sure ?

Re: replacement motor(s) / i3-MK2 ?

You can change the steps required.

Example: Currently the extruder default is 161.3 steps per mm. Double that to 322.6 (or calibrate the extruder to be more accurate). You can either change the firmware and recompile (real PITA having to do this every time) or include M92 in the start GCode:

M92 E322.6

However, setting via GCode would cause the load process to screw up immediately after switch on or reset; the M92 is held in volatile memory.

You would also have to halve the maximum feed rate of the motor.

Precision of the extruder currently only becomes an issue when printing 50 micron layers at low speeds. However, using a 0.,9 degree motor would limit the maximum speed and fast printing with tall layers would become impossible. Swings or roundabouts. Your choice...

All motors on the printer are 1.8 degree steppers. 3200 (micro) steps /revolution.

Firmware settings:

// Steps per unit {X,Y,Z,E}
#define DEFAULT_AXIS_STEPS_PER_UNIT {100,100,3200/8,161.3}

X & Y pulleys are 16 teeth @ 2mm. Z is 8 mm pitch and E is about 6.5 mm diameter (less "bite" (about 0.2mm - tension matters!)

Peter

Re: replacement motor(s) / i3-MK2 ?

#define DEFAULT_AXIS_STEPS_PER_UNIT {100,100,3200/8,161.3}

dosn't this mean 3200/8 steps per revolution -> 360° in 400 steps = 0.9° per step ?

Re: replacement motor(s) / i3-MK2 ?

No, that means 3200/8 (400) microsteps per millimeter.

16 microsteps = 1 step.3200 microsteps per revolution / 16 microsteps = 200 full steps = 1.8 degree per full step

Peter

Re: replacement motor(s) / i3-MK2 ?

thanks for enlighting this issue peter !

by the way, you mentioned that recompiling the firmware is a pain in t.. ..., are there any "how to's" to set up the actual arduiono release (1.8) for this task ?
i've read something about that it's nescessary to rename the lcd libraries provided with the arduino package.

Re: replacement motor(s) / i3-MK2 ?

Jeff

Forum search along with the relevant Prusa GitHub article are your friends here...

Peter

EDIT: have a look at this post: http://shop.prusa3d.com/forum/prusa-i3-kit-building-calibrating-first-print-main-f6/titan-extruder-probelms-t850-s20.html#p6323 Things may have changed since I wrote that though...

Re: replacement motor(s) / i3-MK2 ?

hi guys,
just want to confirm that the steppers are 1.8° ones !
got my spare motors this week (NEMA 17, 42HS40-1704) and just replaced the x-axis stepper (because it is the quite simply accessible) for a test.
printer prints as before !

💡

Re: replacement motor(s) / i3-MK2 ?

Hello,
Do you think it is an LDOmotors? I noticed LDO writing on the motor.
http://ldomotors.com/products/show/42mm-hybrid-stepper-series
Ot it is a custom serie?

Re: replacement motor(s) / i3-MK2 ?

Yes, it's LDO.

Look at the body length of your original motor, this will work.

Thomas

Re: replacement motor(s) / i3-MK2 ?

yes... and there is only one motor with 4 leads and 40mm length: LDO-42STH38-1684.

Re: replacement motor(s) / i3-MK2 ?

Could you please let me know where you can buy these from, as I am looking at buying a pair.

Re: replacement motor(s) / i3-MK2 ?

don't know where you can buy the above mentioned LDO stepper that ron dug out.
even so that the LDO-42STH38-1684 is the only one at their published program that would fit for our prusa i3 mk2(s), the electrical properties differ somehow from the ones that I measured at the motors prusa delivered with the kit.
so i guess that they have set up a custom series for Josef.

but you can get "standard" bipolar NEMA17 steppers with the required dimensions and properties through several stores.
look for example what you can google about the 17HS16-2004S1, which fits as well as the LDO model.
you can get them even through amazon.

Re: replacement motor(s) / i3-MK2 ?

the electrical properties differ somehow from the ones that I measured at the motors prusa delivered with the kit.
so i guess that they have set up a custom series for Josef.

Thanks for the info. That is what troubled me. What you measured and the specs of LDO-42STH38-1684 are different. I'm kind of noob concerning steppers then I don't have any judgement about those specs.
Thanx to your ref I found an other topic on that: http://shop.prusa3d.com/forum/prusa-i3-kit-building-calibrating-first-print-main-f6/are-all-5-stepper-motors-the-same--t1501-s10.html
I would like to buy a spare for the extruder. Past Week, my prints gone wrong due to extruder stopped extruding few times. I finally changed: PTFE tubing, heatbreaker and noozle and now it seems OK but only time will say. That don't cost a lot to start from zero there. But I still wondering if it not the extruder or its wiring going bad.
It is quite hard to make that printer reliable. All my issues for now come from the extruder and its wiring. And I don't find the MK2S upgrade fantastic. Only rods and new bearings are nice. I just better understand what desktop printer classification means. This is our first 3D printer and we don't have the experience of the reliability of previous opensource printers 😉

17HS16-2004S1

What would be the essential difference between 17HS16-2004S1 and Prusa's kind of LDO-42STH38-1684? We know its resistance and inductance but torque, inertia? What does really matter?

Re: replacement motor(s) / i3-MK2 ?

of course all properties matter.
the stepper has to be a bipolar type (4 leads / 2 phases) with 1.8° per full-step.
but mainly torque, max. current and phase resistance are important.
our prusa steppers are driven up to 1/2 amp (extruder stepper in high-power mode), the supply voltage for the stepper driver are the 12V from the psu.
if you do the math and divide the voltage by the current, you'll get 24 ohm. so if your stepper has a higher resistance at each phase, you won't be able to provide the required current. so anything below approximately 22 ohm will do the job, if you'll grant 2 ohm for the wiring, connector resistance and shunt resistors.

furthermore (obviously) the mechanical dimensions... and don't forget the flatened shaft.
of course inductivity has it's influence as well... but usually not at the speeds we use them.