Axis Skipping / Drifting

I know, this topic has been beat to death, but in an effort to get a consensus, please help me out here.

I've read that belts are always the cause, rarely the cause or never the cause. Belts should always be loose, belts should always be tight.

Here is what I seem to think is the case for axis drift. First of all, do these statements seem to be true?

Higher Current (CW on POT) equals more torque and power, but more heat.
Lower Current (CCW on POT) equals less torque and power, but less heat.

Your axis should be as close to friction-free as possible.
Friction causes drag, and drag can lead to skips.
Tighter belts increase tension and this equals more drag.

Loose belts can slip.
Loose wires can cause a skip

Too much heat can cause the motor to "reset" and this millisecond break can cause skips.

Second - My particular situation.
Prusa I3 purchased from Amazon (http://www.amazon.com/gp/product/B00N7I1ZVU?psc=1&redirect=true&ref_=oh_aui_detailpage_o05_s00)

I'm experiencing drifting during prints in the Y-axis. Sometimes right away, sometimes after 5 or 6 layers.

The layers always drift towards the front.

I have physically tried to move my bed in the Y direction while holding the pully steady, and I am unable to force the belt to skip off the pulley on the motor.

The motor gets hot to the touch (not too hot that I can't touch it, but pretty hot). I have a fan blowing on it.

(this one is the kicker)
This only happens when printing circles. I ran two 20 minute prints back to back of some little do-dad (one with Cura and another with Slic3r - same object different slicer) Both printed fine. Went to print a circular device, and before finishing the first layer, nested circles were overlapping in the y axis. (attached images)

This particular printer does not use the MEGA / RAMPS1.4 setup that most others have. There are POTs on the board however next to each motor plug.

My thoughts . . . when the printer is printing the backs and fronts of the circles (closest to the front and back of the bed) the Y-axis is moving at it's slowest, as the x-axis is drawing the front and back of the circles.

Thoughts? Should I try geasing the bars on the y-axis first. With the belt off, the bed slides easily and continues moving a few inches after I let go. Should the belt have any play in it? Mine is super tight. like a guitar string.

Thanks for your patience and help!

Todd

If its a heat issue, the fan needs to be blowing on the stepper driver, not the motor itself. Although if the motor is getting too hot, there might be too much current going to it and that needs to be calibrated correctly.

What type of board are you using? Some of them have greater heat dissipation issues, although in my opinion(not necessarily the general consensus), you should put a fan blowing on the drivers and processor along with heat sinks no matter what. I have mine with a 12v fan wired to the input power so it comes on if the machine is turned on that way I don't have to waste any control pins on it.

Printers also have a max acceleration they can withstand. Even if the belt isn't slipping on the drive gear/pulley, it might be the internals inside of the stepper motor that's actually skipping, as its basically just magnetic fields holding it in place. Try lowering the max acceleration in the firmware and the speed at which you're printing at.

Edit: Also, along with the acceleration changes in the firmware, if you're using marlin try lowering the xyjerk to see if there's a change. In the firmware, its defined as the instantaneous change in velocity and this could be causing the skipping.

Edited 1 time(s). Last edit at 07/26/2015 12:27AM by Swooshman46.

I had some skipping and shuddering problems on my printer, and eventually found the problem was my television.....Seriously!

The problem was actually down to the Ethernet connection causing hangs in the processing due to a HDMI-Ethernet converter I have between my TV and satellite box which was spamming a huge amount of data over the home network, and the problem was actually fixed when a change was made to the interrupt priorities in the firmware.

There are probably a hundred reasons why this is completely unrelated to your issue, but my point is that its well worthwhile considering stupid possibilities and consider EVERYTHING in the printers environment, and even changing the environment itself, I spend a lot of time stripping down axes and doing binary tests to find this issue, and was frustrated by the apparent appearance and disappearance of the problems (ie whether my TV was turned on or off)... eventually nailed the problem when I realised that the printer worked fine in the kitchen yet was crap in my workshop, and the reason was because in the kitchen I wasn't using the household Ethernet, just a direct connection to my laptop.... once we recognised the Ethernet issue it was easy to recall that I recently added this HDMI system to the network

Hi Toodwess

I have the exact same machine as your from the same supplier (HIC) and had the same skipping issue, sorted now at normal printing speed.

This is my setup
My belts are not supper tight, there is a couple of mm deflection when I apply light pressure about 25mm away from the bearing on the belt.
My motors do not get to hot and I have no fan on them, they are just warm (pic attached).
Software i am using is Cura
The manufacture says 35mm/s is a normal printing speed, on small items this is fine on larger ones I can increase the speed with in reason with out any issues.
If I try to print to fast my motors seam to loose position, I have two new motors coming to see if this fixes the high speed skip

Things to check
Printing speed (Slow the print speed down try 30mm/s once you can print at a slow speed then try speeding up a bit at a time)
Travel speed (Slow the travel speed down try 30mm/s match your print speed)
Are all frame parts assembled correctly and tight. ( The bolts sink into the frame material go round and tighten)
Is the Y axes square to the X axes. (Measure corner to corner and adjust if needed)
Are the bearings free and running smooth. (They should spin freely)
Are the Y axes bars straight. (had to replace one of my bars)
Are the pulley grub screws tight. (this is the most common cause of Y axes slipping)
Does the pulley tooth pitch match the belt tooth pitch. (This is on You Tube [youtu.be])
Does the printer bed bounce when you are printing. (I have added an extra bearing on the Y axes now I have 2 each side and stiffened the perspex Y table carrier)

Know Fear