Limit Switches

[dr.steven.james]

I'm retrofitting a CNC and need to know how to select limit switches that are compatible with my Buildbotics controller. Some indicate that they work with Arduino, some don't say.

[Doug]

Any limit switch that provides a contact closure will do the trick. The limit switch inputs on the Buildbotics Controller are just TTL compatible gates that are pulled high to 3.3Volts. The switch contacts just connect that output to ground.

I like the magnetic proximity sensors like these

https://www.digikey.com/product-detail/ ... -ND/154470

They come in two parts. If you buy them make sure you get both parts

[MTek]

I have setup my cnc router with the buildbotics controller and have run the test buildbotics logo and a few of my own designs to cut front panels. The joystick is working great and the sticks match the movement that my cnc router makes in XY and Z. I am now working on setting up limit switches for my machine to home in the lower left corner of my table.

However when I set MOT 0 (Y axis) to "homing mode switch min" the Y axis moves away from me and away from the min limit switch in the wrong direction.

The X axis (MOT 0) does the same thing, with MOT 0 set to "homing mode switch min" the X axis moves to the right instead and away from the min x limit switch.

What am I doing wrong?

[Doug]

If the limit switch is active when you start the homing procedure, the axis will start out in the wrong direction because it thinks it has ready found the switch and starts the back-off step.

This can happen if the switches are configured to be normally open but they are wired for normally closed, or vise versa. This can also happen if the switches are mis-wired.

You can tell whether a switch is active by looking at the icons on the CONTROL page-> I/O tab.

[MTek]

Thanks. That worked for the X axis and it homes well. On my Y axis the M1 looks like mit is homing well. However my second y stepper MOT 3 A is homing and jogging backwards. I prefer to not use homing switches on MOT 3 A. Is there a setting I can change, or is it recommended to have a homing switch on MOT 3 A as well?

[MTek]

I figured this out. I simply disabled inputs # 11 and 12, MOT Limit Max and Min, in the I/O section. Everything is working well now.