Ignoring Endstops?

My roommate and I bought a Mendel90 kit from you in the summer and it's been great so far.

Today after a little bit of repair the printer seems to be moving faster than normal in the X and Y axes and grinds violently against the endstops for a few seconds rather than stopping like normal.

I tested the endstops themselves using the M119 command and they're all working fine, but the board appears to be ignoring them or misinterpreting their signals in some way. I don't understand enough to fully troubleshoot this and I couldn't find anyone having a similar problem online.

The repairs we did were to fix a pretty serious clog in the hotend that we could only fix by disassembing the J-head and clearing out a clog at the very top with a heat gun. Pretty sure this is due to the convection issue Nophead has identified, and I've added a hole to the fan duct as he suggests.

After reassembling everything, all the connections and parts seem to be in the right place, and everything extrudes fine, but the extra-fast movement and grinding against the endstops is puzzling. Any ideas what's going on?

PS: I just remembered that I've also had an issue in the past with the extruder motor turning extra fast and spinning the hobbed bolt against the filament the first time I tell it to manually extrude. The second time it usually extrudes normally. Might be related?

Thanks!

Have you changed speed (feed) settings in your host or slicer programs recently? You do not say where you are observing these problems i.e. manual moves or during printing.

Also, the endstops are generally used only during homing. At other times it is possible to drive the motors against the limits by manual mistake or a bad host/slicer program configuration.

Regards,
Neil Darlow

Edited 1 time(s). Last edit at 01/22/2014 03:15AM by neildarlow.

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

For the X axis, check that your spring bolts/wing nuts aren't sticking out and preventing the x-carriage from activating the limit switch.If your spring bolts are out that far then you'll be slipping on the filament anyway but the wing nuts are easy to miss after a repair.

For the Y axis, try loosening the bar clamps, making sure they're sitting straight (and not fouling the bed movement) then tightening them back up again. If your bed is binding or if the clamps aren't vertical then there is enough tolerance in the holes to make the limit switch just far away enough that it doesn't activate correctly when the bed moves.

If you check the movement by hand (with motors off!) then both axes should move all the way to the limit switches smoothly without excessive pressure, and the springs in the switches should make the axes "bounce" off them without binding.

HTH

@Neil,
The limit switches are only used for homing, but after that the soft limits should prevent the axes crashing, or ever even reaching the end stops.

@lemonade_brezhnev,
There was an issue in the firmware where the axes move faster during homing if one homes before the other. I fixed that on Github. However that only caused it to slam against the switch, it didn't try to carry on. Most likely if you worked on the extruder either the idler bolts are sticking out, or the wing nut it. I can't think why Y would have changed.

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[www.hydraraptor.blogspot.com]

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nophead
@Neil,
The limit switches are only used for homing, but after that the soft limits should prevent the axes crashing, or ever even reaching the end stops.

I totally agree with that but I recall my Y-axis endstop once being hit, and the motor still running, after three 100mm movements in Pronterface. I do not understand how it happened but I found myself dashing for the Off switch.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

Thanks for your help, guys. Turns out it was a simple issue of the spring bolts stopping the X carriage from fully reaching the endstop. Total rookie mistake.

It's unclear what caused the issue with the Y axis but it only happens when I control the printer manually so I'm not too concerned. Maybe it always does that and I just never manually sent the bed all the way forward?

I updated the firmware just to make sure and tried a print, everything's working okay now.

I imagine you can always crash the axes if you move them before homing. One homed it knows where they are and the soft limits stop it from crashing provided the motors don't skip steps.

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[www.hydraraptor.blogspot.com]

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nophead
I imagine you can always crash the axes if you move them before homing. One homed it knows where they are and the soft limits stop it from crashing provided the motors don't skip steps.

Should you actually be able to perform moves without a Home operation being performed first? I does not seem sensible to permit moves in any direction until the firmware has established a known reference position for each axis.

Addendum: In the Pronterface Settings|Options dialog there is a Clamp manual moves checkbox which is useful to prevent this happening.

Regards,
Neil Darlow

Edited 1 time(s). Last edit at 01/23/2014 04:46AM by neildarlow.

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

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neildarlow
Should you actually be able to perform moves without a Home operation being performed first? I does not seem sensible to permit moves in any direction until the firmware has established a known reference position for each axis.

I thought that too, but when I tried it when replicating an issue for another member I found that I could in fact move the axes without homing.

Even if it the firmware were to prevent me from doing this, I can still see a scenario where crashing into the limit switches might happen: if I auto-home, wait for the motors to go idle and manually push the bed to another position, then the firmware has no knowledge of this move. The next G0/G1 move has a good chance of hitting the endstop as the soft limits will now be different from the physical limits.

You wouldn't be able to commission a machine if you could not move until homing because you want to be able to test it moves in the right direction before trying to home.

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[www.hydraraptor.blogspot.com]

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nophead
You wouldn't be able to commission a machine if you could not move until homing because you want to be able to test it moves in the right direction before trying to home.

Perhaps an override like the Cold Extrusion could be used. Still it is useful to know that, despite software endstops, head crashes are still possible and we should take measures to avoid them.

My usual pre-print sequence is:
1) Connect printer in Pronterface
2) Hit the Home button
3) Hit Motors Off button
4) Correct Z screws according to flag displacement
5) Ready for printing

Any manual movement of the X or Y axis would be followed by another Home button press.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

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neildarlow
4) Correct Z screws according to flag displacement

Do your Z-screws need correcting regularly?!

My usual procedure is:
1) Turn on printer
2) Ready for printing

Same here: I just turn it on and print a file which has a home in the start.gcode. I only use manual jog mode to change the filament after commissioning.

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[www.hydraraptor.blogspot.com]

Apparently, when micro-stepping is used on the Z axis you can stop between real steps and when the motors are power-cycled they can jump to the nearest step either way. It is only a one step adjustment (unless you forget to do it in which case I guess they can accumulate).

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.