Prusa Mendel i2 skipping steps, bad quality

I'm building a Prusa Mendel i2 from scratch using Prusa's github files. I've assembled the printer and the extruder. I'm using greg's extruder and a E3D-v5-like hotend with 1.75mm filament.


I'm also using a MK2B heated bed along with an Arduino Mega with RAMPS 1.4 (Marlin firmware) and chinese A4988 stepper drivers.


After measuring and assembling the printer, my attempts at printing (with ABS) have been unsuccessful.
The main issue is that the Y axis seems to be skipping steps, misaligning the print.
I'm using 1.8°, 0.3A motors, as depicted.


Here's a video of one of the printing attempts (a 20mm cube, [www.thingiverse.com], with hotend temperature 235°C, bed temperature 110°C, 0.3mm layer height and 20% infill).

I've already set and checked the VREF on the drivers to match the max 0.3A current rating for the steppers.

I don't know what could be the problem. Any tips?

That's a 12V stepper motor, so you'd need a 24V supply or more to drive it reliably. If you're running it at 12V it's going to be unreliable (counter-intuitive as that may sound).

Reducing the motor speed might help: that usually bumps up the torque a bit. Also, is the rail alignment good?
hth
Dave

Reducing speed helps a bit, but doesn't eliminate the issue. Tried moving the axis at 2000mm/min and even then things aren't smooth. The rails are aligned.

I totally overlooked the voltage rating for the stepper. There's a good chance that's the problem. I'm going to modify the Arduino and supply 24V to the steppers and see what happens.

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gustavsl
I totally overlooked the voltage rating for the stepper. There's a good chance that's the problem. I'm going to modify the Arduino and supply 24V to the steppers and see what happens.

Sounds like a plan - have you checked all the things that need to be accounted for to run ramps at 24v? I haven't done it so I'm not familiar with everything, but if I remember right it includes changing out the polyfuses for conventional ones, checking the stepper driver capacitors are rated for 35V, removing the D1 diode and providing an alternative source of 8V or so to the mega2560.

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JamesK

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gustavsl
I totally overlooked the voltage rating for the stepper. There's a good chance that's the problem. I'm going to modify the Arduino and supply 24V to the steppers and see what happens.

Sounds like a plan - have you checked all the things that need to be accounted for to run ramps at 24v? I haven't done it so I'm not familiar with everything, but if I remember right it includes changing out the polyfuses for conventional ones, checking the stepper driver capacitors are rated for 35V, removing the D1 diode and providing an alternative source of 8V or so to the mega2560.

Yes, you're right. If i'm not mistaken, besides the separate power supply, D1 needs to be removed and the 100uF capacitors need to be at least 35V rated. Also there's a 11A fuse that's rated for 16V that needs to be replaced as well.
I'll try it and report back. Thanks.

I tried supplying 24V to the printer, but the issue persisted. I then tried disassembling the whole Y axis, thinking that the problem might be related to the positioning of the rods or the belt.
After reassembling the Y axis, the problem was solved.
It's not clear what exactly was causing the problem, but I think it has something to do with the alignment of the rods and the belt. Also, the Y stepper motor wasn't very secure in its place, which may have contributed to the issue.

That's odd. Sorry if I sent you in the wrong direction with all that work. If it was actually a mechanical problem it might be worth putting marks on the pulley and drive shaft in case it starts slipping.

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JamesK
That's odd. Sorry if I sent you in the wrong direction with all that work. If it was actually a mechanical problem it might be worth putting marks on the pulley and drive shaft in case it starts slipping.

No problem, I also thought there was something wrong with the steppers. I had made some adjustments before to no avail, so I had ruled out a mechanical problem. Turns out the axis disassembly was needed. Thank you for your help.

hi
you seem to have a problem i had when i first built my wilson,
the main thing i did to correct the stutter/shudder was to follow tom's guide on basic setup,

the most important thing is to get the Stepper Vref voltage right i was at about 0.22 after correcting to 0.34- o.4 the issue was eliminated

[www.youtube.com]

as tom say's "there is no magical number" so get it as close to 0.4 with the motor sound fairly quiet almost like a e bagpipe

what i did was set the printer to print a large square with a circle inside ( make one on tinker) 5mm high
with no filament in start the print

then carefully adjust the trim pot's to the desired Vref - i pre-set them to 3.0 and worked from there

you will hear the motors complaining either way,

- too low is really bad/stutter-shudder
- too high they will scream and run hot, make sure you have a cooling fan blowing onto the stepper drivers at all times

( a good test at lower vref voltage is to place slight, then progressively increase resistance with your hand on edge the (cool bed) on the y axis movement as it moves forward towards you movement during the test print, this will immediately bring the shudder/shit beast out)

once the Y axis was not slipping shuddering, the ref voltage was 0.38 on my stepper, they might be different to yours - find the sweet spot .. i then turned them to 0.35 and did a fair sized print run while keeping an eye and finger on the steppers and drivers they were all cool to the touch 30 degrees about

Edited 1 time(s). Last edit at 05/10/2016 06:31AM by mrtwizta.