Stepper Motor Only Turns One Direction
Hey there, so I recently got my 13th, 14th and 15th Prusa i3's and I'm having trouble with one of them. I'm not a noob by any means, but this one's got me stumped.
Printer was working fine for the first few days of operation, then came in to the shop one morning and a print was half finished with the print head at the front right corner and a "Crash detected" screen displayed on the LCD. Tried to start another print then, it got partway through the first layer of the print before eventually making some awful grinding noises and then banging the extruder carriage into the right side of the printer triggering a crash detection warning.
Through analysis I determined that the problem is that the x-axis stepper motor can only turn in one direction. Even with the printer powered off, you can move the carriage to the right side of the printer, but if you try to push it to the left it gives ALOT of resistance. Is this a faulty motor? I've checked all the most obvious things and I can't seem to find any other possible cause besides the motor not allowing the shaft to rotate.
RE: Stepper Motor Only Turns One Direction
Slacken off the grub screws on the motor pulley so that the motor pulley can rotate on the shaft without moving the motor,
try moving the X axis again.
if it still jams you may have a faulty bearing and it could be either a linear bearing or the idler bearing
(I have had two X axis Idler bearings fail... (Original Equipment) I now replace my idlers on building with cheap no name chinese(I expect) toothed idler wheels with twin bearings instead of the original smooth single bearing offering, (toothed / smooth idler is another matter... I choose toothed so that the lumps on the timing belt are not squashed by the pressure on the smooth roller surface... your choice may differ)
if the x Axis runs quite freely with the grub screws loose, then the fault is probably the motor.
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Stepper Motor Only Turns One Direction
High friction in one direction can also be seizing bearings. Did you pack the linear bearings with grease before installing them? If not, apply light machine oil to the rods and move the axis back and forth unitl it moves smoothly and freely.
Another known issue with the MK3S is the extruder case can be too small, and crushes the bearings making them seize. Loosening the extruder case screws near the bearings has been shown to release the pressure enough to allow normal printing.
RE: Stepper Motor Only Turns One Direction
Slacken off the grub screws on the motor pulley so that the motor pulley can rotate on the shaft without moving the motor,
try moving the X axis again.
if it still jams you may have a faulty bearing and it could be either a linear bearing or the idler bearing
(I have had two X axis Idler bearings fail... (Original Equipment) I now replace my idlers on building with cheap no name chinese(I expect) toothed idler wheels with twin bearings instead of the original smooth single bearing offering, (toothed / smooth idler is another matter... I choose toothed so that the lumps on the timing belt are not squashed by the pressure on the smooth roller surface... your choice may differ)
if the x Axis runs quite freely with the grub screws loose, then the fault is probably the motor.
regards Joan
Will check that in a little bit, do you have any other modifications/improvements that you do upon assembly? I was thinking about starting to do that myself with a couple things, we run a small print farm as a business so I'm always trying to find more to keep my printers running as perfectly as possible.
RE: Stepper Motor Only Turns One Direction
#1: If you do a teardown, pack the bearings with an appropriate grease.
RE: Stepper Motor Only Turns One Direction
Please post your results.
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Chuck H
3D Printer Review Blog
RE: Stepper Motor Only Turns One Direction
So what I ended up doing was this:
Loosened the grub screw and performed the check that Joan recommended, still had trouble moving the carriage to the left but didn't think it was the grub screw.
I then took the back plate off the extruder carriage and tested the bearings for movement problems. All I did was snip the zipties and then try to move each bearing individually and found it was the bottom bearing that was bad.
Rather than start ripping the whole printer apart to remove and replace the bearing, I opted to rub a little grease on the linear rail and then forced the bearing to slide over it. After the bearing ran over the grease and moved back and forth a few times, it completely fixed it.
Lesson learned: check and re-grease linear rails more often (something I actually haven't done since assembling my first Prusa a little over a year ago). I actually ended up having the exact same problem occur on a different printer a couple days later (a print failed partway through, then the carriage would only move one direction) and I was able to fix it by doing the exact same thing.
The weird thing is though, the first printer to have a bearing problem was a brand new printer (less than 2 weeks of ownership), while the second printer to experience bearing problems has been running since May (so about 7 months).
Final note: each of the linear rails that I greased and fixed a bearing on, ended up having a hairball form on the linear rail. Like actual hairs it looked like. Which is weird because all my printers are in a special room that we built in a warehouse, far from any animals.
RE: Stepper Motor Only Turns One Direction
could the Hairs, be Filament Hairs? from extrusion?
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Stepper Motor Only Turns One Direction
The shipping oil that the Prusa bearings comes in evaporates over time. Thus problems of seizing bearings happens a few weeks to a few months after installation. Grease needs to be inside the bearings where it is retained by the grease seals. Greasing the rods is a half-way measure, and oiling the rods is probably a better way to go until the bearings can be packed properly.
But, if the printer is working again ... +1.
ps: as for hair on the rails, do people wear hair caps in that special room? If not, then you know where the hair came from. People shed as bad as most animals.
RE: Stepper Motor Only Turns One Direction
The shipping oil that the Prusa bearings comes in evaporates over time. Thus problems of seizing bearings happens a few weeks to a few months after installation. Grease needs to be inside the bearings where it is retained by the grease seals. Greasing the rods is a half-way measure, and oiling the rods is probably a better way to go until the bearings can be packed properly.
But, if the printer is working again ... +1.
ps: as for hair on the rails, do people wear hair caps in that special room? If not, then you know where the hair came from. People shed as bad as most animals.
Should the bearings be packed with grease during assembly? Or no since it comes pre-lubricated?
All I did was smear a tiny bit of grease on the linear rod, and then rub it around and spread it out really good. It seemed like the bearing absorbed as much as it wanted to and then at the boundaries of where the extruder carriage can move it left a small amount of grease that couldn't be picked up. I did this to about 5 of my printers then and I saw how printers whose linear rods felt dry absorbed a lot more grease than printers whose rods still felt oily.
RE: Stepper Motor Only Turns One Direction
Prusa claims the bearings are prelubricated, but have yet to provide evidence they are. I believe they are not, that they come packed in shipping oil that evaporates. Why? All the manufacturers I've contacted say that unless ordered with grease, they arrive packed in a preservative oil. Believe Prusa if you want; but I grease bearings per the manufacturers recommendations.
Another reason I am confident they are not lubricated? My original Prusa bearings lasted a few weeks before they were scratching the rods. And I read a lot of posts on this forum from people who are experiencing dry bearings, who also believed Prusa, and a drop or two of oil fixed their issues to delay a proper tear down to add grease.
As always YMMV.
RE: Stepper Motor Only Turns One Direction
Second. Smearing grease (or oil) on the rail is just a temporary measure to let you schedule a proper tear-down to pack the bearings.
RE: Stepper Motor Only Turns One Direction
Thanks all for this conversation, it helped me sort out my MK3S last night. It had run great for a dozen small prints after construction, then during a simple print it crazily pushed the bed all the way forward on the Y-axis and continued periodically spinning the motor in that direction, grinding the gear against the belt with a horrific racket. Seemed to clearly think it was still in the right place and printing appropriately but ummmmm no. I checked and tightened the grub screws (nope), then pulled off the bed, loosened the grub screws to turn the Y-axis motor and make sure it was okay, eventually discovered that the right-side bearing for the bed was rolling smoothly forward but not backward. Lubricating the rails with the lube provided in the kit has temporarily fixed things while I print this greasing cap and order some proper lube to pack the bearings with. May order and print spares of all sorts of things to be ready for future adventure. Thanks!