Help understanding what I might be doing wrong.

Let me explain. . .
I have built my gantry style CNC and am using a gecko 540 driver with 3 nema 23 motors. I have tried configuring the 6 switched (at the max and min of each axis) as all limit switches and with 3 as home and 3 as limit)

During this project, I have been taking it 1 step at a time, making sure that I have the correct understanding of how each component should work and that is does so before I move forward. This is where I would like a little guidance as I am not sure I have things correct. I have been trying to run the test patterns that come with LinuxCNC to make sure my Z, Y, and Z axes operate correctly. (Note that I have not yet installed the router on the Z axis. It is currently just an empty sled.) However I am having difficulties getting them to run correctly. I either have an Z, Y, or Z axes that has the incorrect + or - ranges, or while running, they slam into one of the limits unexpectedly.

Could anyone give me any advice on where to start? I am not sure I am even in the correct location to be asking these questions. As an example, on the Z axis, I have made the assumption that when it is at it's top most limit, that it would be considered "Homed" and that as it is lowered, that it's position would be a negative value, but that does not seem to be the correct assumption.

So if anyone would be so kind as to give me some ideas, I would greatly appreciate it.

Thanks

Carl

BigJohnT wrote:

Have you set the scale for each axis and verified that the commanded move is the same as the actual move?
JT

Probably haven't set the scale. I did the stepper wizard, but ran into a micro stepping configuration issue with the gecko driver. In the end I had to set each axis's micro step to 5 (was supposed to be either 10 or 20) . But truthfully, I did not see any scale options. and for commanded movement, the physical machine moves up down, in out, left right the same as the digital one on screen.

BigJohnT wrote:

Have you seen my tutorials ?
JT

No I haven't, are they on you tube? I looked at your profile and did not see any links

Cool, thank you. I will take a look at it tonight when i get home.

I will take a look at your tutorials and go from there.

Ok I did some reading and learned a few things. I took this knowledge home and put it to use. Now I am even more confused. So maybe you can help me figure out where I am going wrong.

There are two issues.
1) Setting up the 6 switches I have at the limit of each axis is proving a challenge. I have each of the axis’s minimum limit switch going to an input ( X to 1, Y to 2, and Z to 3). Those 3 switches are wired for normally closed. The 3 maximum switches are wired in parallel for normally open and connected to input 4. This was originally wired this way so that the 3 minimum limit switches could also function as the home switches. Unfortunately I have discovered that this is an unsupported configuration. So I have just set the 3 min limit switches as the home switch and not defined any limit switches until I get another parallel card for more inputs.

Is this a problem? I tried setting the minimum limit switches to act as home and min limit, but every time I homed an axis, it failed and reported a “Joint” error.

2) I have tried configuring my Z axis and am having all kinds of issues. The only difference between its configuration and the X ,Y axis config, is that is uses negative values instead of positive in the home location and table travel fields. If I set the values to a positive value, it will home correctly. However when I run the test gcode, it crashes in to the upper (top) limit (home) switch every time. When I reset it to have a table travel of 0.0 to -4.25 and a home location of -2.0 (home switch location is still 0.0) it fails to home and reports the following error.
“End of move in home state 7”

Any thoughts? Am I missing the obvious?

Any help would be appreciated.
I can post photos of the machine if needed.

Thanks

Carl

Ok, so I have changed the limit switch wiring, but now my X and Y axis are trying to home by going the wrong direction. When it starts it's homing run, it moves toward the max limit switch and not the minimum limit switch. I went into the config wizard and reversed the X and Y inputs, but then I get a "Joint on limit switch" error. am I missing something obvious?


carl

and just in case I goofed up the config, I manually verified that the axis move in the commanded direction.

All kinds of lost now..

it's usual to home to max z etc , as this would then home away from anything that was previously mounted
useful in lets say a mill or lathe , but in the case of a router then x and y can be set at minimum and your z set to home to max

then you would use the touch off in axis to then set your working point zero , which is totaly seperate from the home points

think of home as being the machine starting point and the touch off as being the work machining zero for use with gcode etc
the docs have some explanations of this ..

if you need home at a minimum point this can be done by changing the net of the limit switches to both-min rather than both-max