Carriages crashing into motor ends..

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Carriages crashing into motor ends.. RichieC 9/21/12 3:58 AM
If i try to move the print head close to the corners of the bed it causes one of the carriages to continue down past the point where the arm is horizontal and crash into the end of the smooth rod motor ends.

If i send a G1 X90 Y90 command to move close to a corner, everything is fine, but as soon as i go further than this (i.e. G1 X91 Y91) it causes the carriage to crash into the end!
The same happens when trying to move to the other corners too, but obviously with a different carriage.. 

Does anyone else have this issue / possible fixes for this ?


Re: Carriages crashing into motor ends.. Bill Culverhouse 9/21/12 4:19 AM
By my understanding in isn't an issue, it's a limitation.

Though it would be nice if the firmware wouldn't allow movements that
are outside of printable area, given the configured geometry, and thus,
that would lead to a crash.

You just have to make sure that your print is inside the print cylinder.

-b



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Re: Carriages crashing into motor ends.. RichieC 9/21/12 4:55 AM
I can see what you're saying, I know that the print area isn't square (more like a circle/cylinder) but this would mean that it has a 90mm radius, which is not quite correct as if i move just the X or Y axis on it's own it can move to 130mm either way. Id be interested to know what kind of area/shape the print area is - im guessing more like a hexagon cylinder shape? If this is the case it might be better to mount the heated bed at a 45 degree angle, as this would give you more printable area in the X or Y directions..

It would be good if the firmware prevented moves that are outside of the printable area and that would cause a crash, as this could ruin a long print, especially if you had overhangs near the top of a tall object!
Re: Carriages crashing into motor ends.. Tyberius Prime 9/21/12 5:55 AM
Depending on the position of the rods, it's either a hexagon, or a rounded triangle.


Re: Carriages crashing into motor ends.. Johann 9/21/12 1:11 PM
Thanks for the feature request, I agree there is room for improvement in the firmware. We should probably ignore G1 commands that would move outside the print area, and maybe send a message back to the host, similar to the existing "cold extrusion prevented".
Re: Carriages crashing into motor ends.. RichieC 9/21/12 3:06 PM
I would be good if an error message was sent back to the host software when attempting to do a move to an invalid outside of the printable area. The question is, how easy would it be to calculate if a requested coordinate is valid or not?
Re: Carriages crashing into motor ends.. Johann 9/21/12 7:34 PM

The simplest is probably to require that each of the three carriages should always be at least 50 mm higher than the end effector (moving platform). The 50 mm could be adjustable as a firmware setting.

Re: Carriages crashing into motor ends.. Sousoux 9/22/12 1:18 AM
On Saturday, September 22, 2012 4:34:53 AM UTC+2, Johann wrote:
> The simplest is probably to require that each of the three carriages should always be at least 50 mm higher than the end effector (moving platform). The 50 mm could be adjustable as a firmware setting.

My assumption is that negative square roots in the delta calcs cause these sudden crashes. I will be checking for that.

Re: Carriages crashing into motor ends.. RichieC 9/22/12 2:16 AM
Checking for negative sqroots sounds like a better solution, if that is indeed what is causing the issue, but checking/limiting the height of the carrages above the end effector also sounds like a viable idea .. The problem only seems to occur when one of the carrages goes below the end effector - which forces the arms on that carrage to go past the horizontal point - then the carriage just continues moving down until it hits the end its travel. So I recon If you limited it so the carriages so the cant move lower than the end effector it would fix the issue.