Hello, and Limits

[mrecircuits]

Hello!
My new Buildbotics controller arrived in the mail last Friday, and I’ve been integrating it into my CNC setup this week. I was interested in this controller mainly because my Linux/EMC2 set up was always so unreliable, and was as old as my mill - getting near 12 years old. I like how the Buildbotics is web based, and I can eliminate using a desktop PC all together.

I think I never had some things set up properly on my old system. It was always giving me errors that only cleared after rebooting the computer and rehoming. Since I’m starting over, I’m trying to get things set up correctly from the beginning. Everything seems to be running great so far! I still need to set up the motors and homing correctly.

The mill I use is a 3-axis Lumenlab M3 with a 19.5" x 19.25" work space. The X axis uses two motors, with only minimum limit switches. The Y and Z limit switches are at the max ends (Z’s limit switch is all the way up). Interestingly, I had to set the Y and Z to reverse. I’m able to home Y and Z, but whenever X tries to home, it just goes into E-Stop. There are limit switches on both X axis motors.

I’d like to get it to home the way I’m used to doing it with the old set up. The Z axis runs up until it hits the switch, and then runs back down 3.25” and offsets to 0, the Y axis runs to the end and then back down 19.25” and offsets to 0, and then the X axis goes to the minimum, then backs off and zeros.

Thanks for any help. I’ve been using this mill for many years, but I’m still very much a novice!

Mike

[Doug]

Hi Mike and welcome to the forum.

You will only be able to use one limit switch for homing on each axis.

You can set the 'zero backoff' distance in the motor configuration pages. This position will then be set to the 'minimum soft limit' if you home to a minimum switch and the 'maximum soft limit' if you home to a maximum switch.

If the wrong switch activates during homing, it will cause the machine to go into estop. Please verify that you are homing to the right switch.

[mrecircuits]

Thank you Doug! Do I need to physically disable the other limit switch on the axis? Like remove M1 limit from the DB25 if I'm using M0's switch? I know only one motor's limit is configurable if two motors share an axis. I'll try tomorrow.

[Doug]

No, you don't need to disable the switches.

You need to determine whether a switch being activated and causing the estop. The icons on the I/O page will provide a real-time display of the state of the switches. This can be helpful in determining whether the switches are working correctly.

[mrecircuits]

Thanks, Doug. First off, I went ahead and changed the orientation of the mill so that now the 2 motor axis is assigned to Y, and made the single motor Y axis assigned to X. That's something I wanted to do for years to speed up homing, and to leave the bottom of the work surface open. I just made the changes in the motor configuration page.

I'm still having the homing problem where it goes into E-Stop. Motor 0 and Motor 1 are controlling the Y axis, using pins 3 and 5 on the IO. I just disabled pin 5 rather than remove the wire. Now when homing, if I manually actuate Motor 0's limit switch, it appears to act as it should and starts the Back Off as expected. Doing the same test, if I manually actuate Motor 1's switch, even though it's "disabled", it goes to E-Stop and Pin 21 goes high.

Is there anything else I should do, besides removing Pin 5's wire all together?

[Doug]

Pin 21 is an output pin. What is assigned on it?

I may be able to provide more help if you attach a bug report to the posting. 'Bug reports' provide a copy of your log files, the configuration of your controller, and the program that is currently loaded.

You can create a 'bug report' by clicking "Bug Report" on the Settings->Admin page. That will create a compressed archive file and prompt you to save it. After saving this file, attach it to your posting.

[mrecircuits]

Hey Doug, thanks for the reply. On Pin 21, I'm not using it for anything, but I noticed it goes high when in Estop. I assume that's normal.

I did some further delving over the weekend, and I did end up physically removing the switch input on Pin 5. Since M1 is always going to be coupled with M0 on the same axis, I figured there was no reason to keep it connected. That seemed to fix the problem I was having, for the most part.

I'm able to home all axes now MOST of the time, but not all the time. I'm having this problem with all axes... When homing, quite often everything goes into estop when one axis gets to the home switch. No more than one switch at a time gets activated, but I can't figure out why this is happening.

This is how I have M2 set for limits (just experimenting):
Search Velocity = .254 m/min
Latch Velocity = .05 m/min
Latch Backoff = 35mm
Zero Backoff = 25.4mm

All the switches seem to work okay, and I've cleaned all of them. What factors make the controller go to estop?

[Doug]

It sounds like you may be getting RF noise on your limit switch wires causing them to trip. Please ensure that:

• you run a ground wire along with the active wire all the way from the limit switch to the controller

• The ground wire is twisted at about on turn per inch with the active limit switch wire.

This will make the limit switch wires much less susceptible to noise.

[mrecircuits]

Okay, I can try that. Should I just ground one side of the shield? The switch wires are bundled in the same cable as the motor signals. I used the same cables I already had in place that terminate to DIN connectors. Should I add pull down resistors to the limit pins in the DB25?

Thanks!
Mike

[Doug]

Do not run the limit switch, estop, probe, or spindle control wires in the same jacket with the motor wires.

Run separate twisted pair wires for the limit switches. They don’t need to be shielded cable, just twisted.